Dr. Leonard Spinu: >> What I'll do today, it's
nothing very special,
other than actually show how we
can just measure some FORCs,
and probably we could do something more direct.
I saw that in Josh's lab, actually,
they have three wonderful instruments
that could be used for that.
But at the time we had in mind,
I wasn't aware about that.
The way I'm going to work today is I'm going
to use TeamViewer hooked
up on my computer in New Orleans,
which is going to project the desktop computer I use on
PMC Laser VSM to get some data.
At the same time, I'm going to use a Skype video feed
and audio feed with my students,
actually going through all the steps
for measuring the FORC and
actually going and get the sample and load the sample,
center on the VSM,
then choose the right parameter.
First, we're going to run probably
a major hysteresis loop to
see what magnetization we have.
Then from there, we try to
find the best parameters
to run some FORCs and see how this works.
The same file actually,
I hope will be able to be used by
Rich and his FORC processing.
Therefore, I'm going to start right
now projecting my screen.
I hope everything is going to go okay.
I never did this before,
and this is a recipe for disaster,
but I hope it's going to work.
I have the backup, a video,
but I think it'll be fine.
Well, I'm going to project my screen right now.
This is my lab in New Orleans.
Now I'm going to put some audio
and if my students are going to hear me,
they're probably going to introduce themselves. Hello?
MALE_1: Hey, Dr. Spina, can you hear us?
Daniel Adams: Hey. Can you hear us?
Dr. Leonard Spinu: Yes, very well. Myself and
about 50 other people.
Daniel Adams: Hi, I'm Daniel Adams.
I'm a student here at the University of New Orleans,
and I'm going to take you through
a typical FORC measurement for the VSM today.
First, I'm going to put a little bit of
vacuum grease on this sample holder to keep it in place.
Today's sample, we're working with
some nanowires grown in an alumina oxide template.
This is a lab grade,
so the template is high quality.
I just want to mount it on there,
make sure it's on pretty well.
Then I'm going to walk over to the VSM,
make sure this compression screw is a little loose.
I'm going to insert this metal rod
and make sure I'm not holding down here.
I want to hold onto this metal so I don't bend and break.
What I'm going to do is
align the groove by turning it slightly,
finger tightening, you can
give it a little bit of an alignment.
Dr. Leonard Spinu: Make sure you do
it by the manual because we have
the Lakeshore people here hearing
and if everything goes fine,
maybe the warranty or whatever, it may be a problem.
Daniel Adams: [LAUGHTER] Yeah, sure.
Dr. Leonard Spinu: For Brad and all the other crews here.
Daniel Adams: I want to start [inaudible].
Our nanowires have grown perpendicular to
the plane of the template, so they're facing out.
For this particular sample,
that's going to be our easy access,
so that's what we're going to take a look at
today and get a nice-looking port.
I'll release this locking mechanism
here so I can slowly lower it.
It has a counterbalance in the back so it doesn't just
completely fall into the VSM.
Slowly center it between these two magnets and I'll back
out a little bit so you can check out our magnetic setup.
The magnetic cores are
about a half-inch gap that
gives us around two teslas or a little bit more,
and you can see the pickup coils are in between to detect
the change in voltage on the sample while it vibrates.
I'm going to do a little bit of centering.
We have an X access over here.
The Z access is right here,
and there's a Y access in the back.
I can release this a little bit, move it up and down.
Make sure it's locked in place.
Now, I have a choice of turning on the vibration
setting here or I
could walk over to the program and I can turn it on.
Are you guys on TeamViewer right now?
Dr. Leonard Spinu: I'm not there yet.
Therefore, just go and we're going to start
TeamViewer when you actually start the measurement.
Daniel Adams: I'm about to run a major hysteresis loop,
so you might want to turn to TeamViewer
so I can talk to you guys about that.
Dr. Leonard Spinu: Let me put
the TeamViewer for a second.
Let's see how it goes. Go ahead.
Daniel Adams: You're on?
Dr. Leonard Spinu: Yeah.
Daniel Adams: I'm going to run
an initial hysteresis loop on
our sample to get a few parameters.
The main ones that I can take a look at
are where is the sample saturating
and I point to where I want to
find the first reversal field.
Before I go to that, I want to apply a field
around one tesla to see my magnetic moment.
As you can see, there's no magnetic moment here.
Once I initiate the head drive to start vibrating,
we get a signal.
I'll match my sensitivity with the magnetic moment,
come down to 10.
Then I go to my measurements,
direct moment versus field,
as you can see, our first-order reversal curve is here.
Right below that is the hysteresis loop.
I'll click that and then as you can see,
I'm already at one tesla,
so I can still enter 10,000 where it says one tesla.
This sample has a pretty high magnetic moment,
so I'm just going to leave it as
is and it's going to take about a minute and 30 seconds.
We'll go and you can see the red line chase
across the screen pretty fast.
Dr. Leonard Spinu: Can you magnify
the window with the data?
Daniel Adams: No, I can't make it any bigger.
Dr. Leonard Spinu: Leave it like this.
Daniel Adams: It's fine.
Dr. Leonard Spinu: You see
that it's pretty fast, actually.
You can get a loop in about run into
something with two minutes before we are using PMC.
Daniel Adams: I like measuring nanowires with FORC.
They tend to be a little bit more well-behaved than say,
multi-layered samples that have many different steps.
This line here is pretty smooth,
so you'll get some nice FORC curves out of it.
But that could also be not as fun
as something cool as something with multiple steps.
Dr. Leonard Spinu: Just a quick question. What is
the average time did you use for this measurement?
Daniel Adams: This measurement, I used
100 milliseconds or 0.1 second.
Dr. Leonard Spinu: Base, 10 points per second?
Daniel Adams: Yeah. It's done.
There's no need to save this
necessarily unless I want to present it to somebody.
The parameters that I was talking
about were where does this sample saturate?
I would say the sample saturates completely around,
let's say, 6.5 kiloersted.
I typically take it a little bit further to
around maybe 7,000-8,000 to make sure that I get it.
The next parameter that I
want is my first reversal field,
which I'll take it to be around around 4,000,
to make sure that I grasp everything.
Dr. Leonard Spinu: Can we just put a little bit
of why you take these parameters?
Daniel Adams: Sure. If you look at
the FORC plane, let's say,
our reversal field and our applied field,
and you rotate that,
you get your interaction field and your coercive field.
Wherever it saturates is where you're going to
get your interacting field plus the coercive field.
I do a small equation that is
H interacting plus H coercive equals H saturation.
If I have the saturation point and I
have the interacting point,
then I have my coercive field roughly.
Also, after doing this for years,
you tend to be able to just
eyeball where you want it to go.
I wrote down my parameters that I wanted.
My saturation field was 8,000
and my interacting field was 4,000.
If I subtract that,
I get my coercive field to be 4,000 as well.
What I'm going to do is I'm going to click out of this,
put on my measurements, direct
moment versus field once again.
Dr. Leonard Spinu: One second, Daniel.
I would like to say a few things about this.
Daniel Adams: That's fine.
Dr. Leonard Spinu: Because I would like
to mention about different
FORC options, different menus.
I know that actually there are
different ways you can take the FORCs.
One way that was originally
implemented by PMC and then by Lakeshore
is the fact that you have
a protocol to use a minimum amount
of measurements in such a way that you get a diagram,
so you don't measure in places
where actually the distribution is known to be zero.
To make myself clear, what I'm going to do,
I'll try to make a drawing on my OneNote here.
For example, when you have the plane like
this and we have
the reversal field and the applied field.
Therefore, you expect you have
a distribution somewhere here.
Now, the complete set of FORCs,
you're going to be measuring everything here from left
to right, like this.
Even for example, here,
you don't have a distribution that is significant.
That's why the way
actually the software were implemented,
you start from somewhere here.
You choose the point HB1
and then you basically don't measure this corner here.
I don't know if Harry can correct
me if I'm correct or not.
[LAUGHTER] That's why for the problem,
that sometimes when you use the usual menu,
is that you don't choose the right value for HB1,
and you may clip the distribution.
If you have, for example, large distribution here,
you may clip it here.
Also, another parameter that is neede,
is the coercivity,
how long you measure, for example.
Because here, then instead, you get the saturation.
Therefore, if I get the saturation,
I've got to get all this.
But if you want to minimize the measurements,
don't extend too much in place.
For example, if your distribution is here,
you don't need to go somewhere here.
That's why you actually get the FORC in this region,
this square to measure.
That's why another parameter if we want, is Hb1,
Hb2, Hc1 is usually zero, and Hc2 here.
Actually, if you don't choose properly the Hc2,
you can basically cut and clip your distribution.
Therefore, that's why you need to be careful
in the way you measure the FORC.
Then it went a little bit over
how you choose this parameter that he mentioned.
He's doing this for quite a time,
and he has experience how to do it.
But actually, first,
you do a major hysteresis loop,
you see how it's saturated,
and actually, you use
this parameter and also the shape
of the hysteresis loop to choose that.
But we were fortunate to have a good relation with PMC,
and actually, they implemented a menu
in the software that you can extend it for.
For example, you can measure all these things.
Actually, sometimes you may
feel that this is overkill but
this method has a certain advantage.
First of all, it may take a little bit longer,
but if the signal is strong and
it can use a very small average time,
therefore, it's not significant
the amount of time added to measure this portion here.
The advantage is that sometimes you like
to use a processing software like FORCinel
that I'm going to show in the second part of
this morning and you like to present the data,
not in the rotated coordinated system, Hc-Hb,
but for example, in the reversal and H coordinate.
That point, it makes sense
to have all the data
because when you try to make a graph,
if you use just the reduced scheme of measurements,
you may have problems when you rotate it or when you
use this reduced scheme.
I don't know if you can show
this part in the menu. I can try it right now.
They need to go to TeamViewer.
I don't know if you can show those two different options
in terms of reduced FORCs and extended FORCs.
Daniel Adams: I'll share the extended FORC first and then
we'll run an experiment in the class.
>> The extended FORC,
you simply enter your saturation field.
In our case, it was 8,000 oersted.
Then the field that we wanted our initial FORC
was around 4,000 oersted.
Every time it's going to saturate,
then come back and start ramping down.
Then our final reversal field will be
-4,000 as well or actually at our saturation field.
It goes from positive saturation to negative saturation.
You get the whole entire curve,
which it takes a little bit of time,
but you get everything.
That's the advantage as Dr. Spina was saying.
Now, let's go to our other FORC.
A lot of times I used to use a protocol where I'll do
the extended FORC first and then adjust
my parameters since it only takes an hour or two to run
the FORC with extended.
I'll go here and I'll enter my saturating field first.
That was 8,000,
and then my Hb min is a -4,000,
and Hb max is 4,000.
Now, the only reason why I know
this next step is because I've dealt with nanowires,
and they tend to have
a larger coercive field because they have
this phenomenon that happens
where they have this tail that comes across.
I'll tend to do a little bit further around 5,000.
I go to details,
and it's going to tell me that I need a field
larger than 10.18 kilooersted.
I'll saturate it at 10,200.
Depending on my signal,
I'll increase the averaging time.
The previous user used three seconds.
That's too much for us today.
Let's see what two looks like at 100 FORCs.
That'll be around 36 minutes.
Dr. Spina, is that something you
want? Thirty six minutes is good?
Dr. Leonard Spinu: >> It's okay. I think it's fine.
What you're going to do when
you are comfortable with parameters,
you can launch the sequence,
and you can show on the screen how it appears,
and actually, I see a few things.
Daniel Adams: >> Then by the time you finish
your seminar, we'll be finished.
Dr. Leonard Spinu: >> Probably, good.
Daniel Adams: >> I'm going to execute, make
sure the head drives on.
What happened there? It tells me something different.
We got 11. There we go.
Thirty four minutes, so 35 minutes roughly.
Now, the sequence is running.
You'll start to see the FORC form around right here.
It doesn't collect data from here to here to here.
That's a good aspect. You're limiting
the amount of data by doing it this way.
Dr. Leonard Spinu: >> As you see right now, the first FORC
are getting taken here.
It's pretty fast, and actually here,
you have on the menu,
some information,
what measurement is doing and how much time is left.
I don't see very well here.
I see 34 minutes or what?
Daniel Adams: >> Thirty four minutes.
Dr. Leonard Spinu: >> Thirty four minutes. Obviously, we're
going to take some time to do this,
which is not that long,
and this is the reduced scheme of works
that was originally implemented in the software.
Actually, this is the file that actually,
I think it's expected by forking L. I know there are
several options in terms of data file formats.
I know a previous FORC NL version.
You're like first generation,
second generation, and so on.
Also, I know that once
we implemented this extended FORC,
Rich implemented also the option to
get this extended FORC into FORC mail,
which can be used.
Daniel Adams: >> I would like to add to keep in mind
that we're doing a very quick scan,
so the FORCs are going to be a little
bit noisy, but that's okay.
Dr. Leonard Spinu: >> Actually,
this would be a good way to do it
first when you have a specimen or sample,
you don't know too much about it.
It's no point to take 500 FORCs and
wait for five hours and find out that
something was not as you expected as a suggestion.
It's just basically we do run a quick scan
and we see where we are and also we process it,
and sometimes, as I mentioned,
may have this situation that the FORC,
it's clipped and we need to readjust the parameters.
I'm looking at the watch.
It looks like I have a little bit of time to fill,
and this doesn't take too much time to get the FORCs.
I guess it's taking more to understand them,
and I guess yesterday we tried to help on that.
But if you have any questions in terms of how we
do it or for my student be able to.
Excuse me. If they're
any questions. Go ahead.
MALE_2: >> I was wondering how you chose the
4,000 oersted for Hb max.
Can you explain that again?
Dr. Leonard Spinu: >> Danny, the question, how you choose the
4,000 value on the field? This is the question.
Daniel Adams: >> In the major hysteresis loop,
I took that's where
the bend of the hysteresis loop was started.
Whenever it starts to bend,
that's my first reversal field,
and if you look on the plane
HRH and you rotate at 45 degrees,
you get our interacting parameters
and our coercive parameters.
Our interacting parameters basically along
the same line as our reversal. That's right.
Dr. Leonard Spinu: >> Well, basically,
we have a certain size of sample.
We are working a lot with nanowires,
and when you have different samples
from nanowire sample to another one,
we have a parameter change like
the length of our wires and the distance,
but the shape of it remains about the same,
and doing FORC for so long,
we know we had this issue that
we got the first diagram clipped.
That's why I need to readjust the parameter.
A rule time we have is that when you have
saturation and then we start curving and going down,
the demagnetization decrease, therefore that
is the place we're going to put our Hb,
the field at which we have this band.
But of course, this doesn't work
probably for all these shapes,
and may have situation of this doesn't work,
but what Danny was
using and it looks like it works for him,
this is the situation. Yes, go ahead.
Ron: >> I'd like to ask a general question about
how demagnetizing factors taken into
account in FORC analysis from
the major loop that your student showed at the beginning,
knowing that this is a array of nanowires,
it seems to me that because there's
a clear demagnetizing factor effect,
this is either a dense array of nanowires
measured with the field
perpendicular to the plane of the array,
or it's a sparse collection of nanowires,
with the field applied
transverse to the axis of the nanowires.
Guessing it's the first,
that it's dense array.
Dr. Leonard Spinu: >> Actually the fields apply along
the axon nanowires and
nanowires are pretty close with each other.
Ron: >> They're very close together.
Effectively, the demagnetizing factor
is that of a plane or close to a plane.
In other words, a rather large demagnetizing factor,
and that's what gave rise to
the shearing of the hysteresis loop
that was very evident in the major loop.
Now, the FORC analysis depends on
the second derivative of the magnetization,
which is the first derivative of the susceptibility.
The susceptibility in a ferromagnetic material
is highly dependent on demagnetizing factor.
That is the measured susceptibility.
The general question then is,
how are these effects taken into account in
the FORC analysis or does it matter at all?
Dr. Leonard Spinu: >> Well, of course, it's important.
Actually, in the case of Nickel nanowire,
this is well known that actually
when you have the interaction,
this effective interaction can be taken into account as
a modification of
demagnetizing field or demagnetizing factor.
Actually, there are certain models,
and actually this is the way you treat the interaction.
You add up actually
a demagnetizing field which somehow
is related to the porosity of the membrane,
and actually, this is the way you do it.
But now, to answer your question,
while you take the data,
you just take your data,
and therefore when analyzing them,
there are certain options that you can do after that,
even the forking L, and Rich can say more how you
can correct some of the effects,
like you have a parametric slope and even diametric.
But in terms of your question of demagnetizing field,
for this particular sample,
it's nothing that you do
specifically for how to get another FORC
because what you see we share is
just a expression of the interaction between other wires.
I don't know if I answered your question. Please.
MALE_3: >> Actually, Ron brings up
a really good point, I think.
For these particular samples,
my feeling is there's no problem because, in fact,
if the field is along the axis of these nanowires,
it's like a needle,
and the demagnetizing factor is very small.
But if it were perpendicular to the axis,
then it would be a large effect.
But to take this one step further,
if you're dealing with these rocks the geophysicist here,
it seems to me that that could be a big factor here.
Obviously, one should be using
the internal field to this in the sample,
and so in these macroscopic type materials
which are ferromagnetic,
then the effect of the demagnetizing factor,
reducing the external field to give you
your internal field is an important parameter,
in which case, all these FORCs should really
be analyzed in terms of the internal field of the sample.
Dr. Leonard Spinu: >> Yes. Just follow up
Ron: >> Just to elaborate on the point,
even though the measurement in this case
is along the axis of the wires,
the fact that it's a dense array means
the effective demagnetizing factor
is not that of a single nanorod,
but it's effectively a plane
because they are close together.
It has to do with the packing density.
MALE_4: >> We don't know that.
Ron: >> There is some demagnetizing factor
clearly because of the shearing of loop.
Otherwise, your loop would have been vertical.
You would have not had any sharing.
It's clear there is an effective demagnetizing factor.
If I'm not mistaken, a lot of the analysis
has to do with the differences in
susceptibility from one FORC to another FORC,
if I'm using the terminology correctly.
There's small differences in
susceptibility for each suite.
Dr. Leonard Spinu: >> Just get it across,
and see how it is.
Ron: >> If you consider the case of,
let's say, a ferromagnet.
Let's consider a small cylinder or a needle,
just an isolated needle
where the susceptibility, it's a ferromagnet.
The susceptibility is infinite.
Are you going to be able to
detect the internal susceptibility is infinite?
Are you going to be able to detect the difference in
susceptibility from one FORC scan to another FORC scan?
You may not be able to do it.
Dr. Leonard Spinu: >> Now, coming back to
the point mentioned about the demagnetizing factor,
I guess also you can make distinction between
the demagnetizing factor of the wire itself or
one wire and demagnetizing factor
of the sample itself because as you mentioned,
if you have, let's say, a dense array of nanowires,
let's say the limit when porosity is one.
>> Actually, it's like a 10 film.
At that point you apply
the field perpendicular to the surface,
you have a 2Pi demagnetizing factor.
Now we have, let's say something in between, of course.
We have the field applied to wire
which minimize
the demagnetizing factor of individual wire.
But when you have that array,
you have, of course,
depending the distance between wires,
you have overall demagnetizing factor of the sample.
MALE_5: >> That's right.
Dr. Leonard Spinu: >> Another question? Yes, please.
MALE_6: >> I just
have a more technical question.
When you set up your FORC measurements,
you have two options basically for
the sweeping mode or the field.
One is continuous and another is discrete.
Right now, it looks like you're using the discrete mode.
Any particular reasons for preferring
one with respect to another?
Dr. Leonard Spinu: >> When you go in discrete mode,
you actually have the field stop,
take the measurement, and move on,
and actually you have higher [NOISE] chances
to minimize noise, basically.
This is the reason. But it take
probably a little bit more time, but actually,
in this case, it's not significant,
and that's why you try to avoid the noise.
MALE_7: >> Responding to the previous question,
I suspect this is being run
in continuous mode, not discrete.
Dr. Leonard Spinu: >> I don't know, I need to ask Danny.
Danny, do you hear us?
What is the mode that is around the FORC? Is discrete or?
MALE_8: >> [inaudible] do you hear me?
Dr. Leonard Spinu: >> Yes. Do you hear me?
MALE_8: >> Danny stepped out for a second.
Dr. Leonard Spinu: >> I said, what mode is around the FORC?
Discrete mode or what?
MALE_8: >> I don't know what he's running it.
Danny stepped out the room for a second,
he'll be right back. [LAUGHTER]
MALE_7: >> But my point is, I think we're seeing it
stepping in the display because of the video link.
I think we were seeing it directly,
it would be a continuous picture.
I'm not certain of that,
but I suspect he's running in continuous mode.
Dr. Leonard Spinu: >> Daniel was taking care of the camera and
actually was not paying attention what Danny option is,
and that's why he's not okay.
But anyway, we have this option.
Sometimes if you want to do it fast forward,
you basically run it
and continues on. Any other questions?
MALE_9: >> I just wanted to make another comment about
the mean field, the demagnetizing factor.
I did make a version of
my software once for someone that allowed you
to put in a demagnetizing factor
and de-shear the FORC data when you process it.
The idea being that when you see these wish bonds,
if you put that parameter in,
you can collapse it all back down onto
the symmetric distribution like we saw yesterday.
It's not built into the current software,
but it's something I'm doing.
Ramon's very FORC software has that feature built in.
It's not something you have to take
care of when you do the processing,
but if you're interested in correcting for
the demagnetizing effects of your sample,
then that is an option and something that people do.
MALE_10: >> Another comment to follow
up on Ron's question.
Indeed, as Bob was saying,
with the field parallel to the nanowires,
the DMC for the wire itself is essentially zero.
But you can actually measure
the dipolar interactions between the nanowires.
In the perpendicular case,
you have demagnetizing dipolar interaction.
Indeed, you share the loop,
and that's why we saw in the advanced materials paper,
you see the square,
the boxes [NOISE] all
shared and you get
a vertical ridge in the FORC distribution.
We also reported in
the scientific report paper in the nano.array,
we purposely prepared
magnetizing and demagnetizing dipolar.
Again, demagnetizing tied the FORC features vertically.
You can say it's rotating it clockwise,
and then the magnetizing one
too is in the opposite direction.
So the dipolar effect can be
studied from the FORC distributions.
Dr. Leonard Spinu: >> Questions?
MALE_11: >> Thanks, it's on a different topic.
A lot of geological samples that are coming into
the IRM are not regularly arranged nanowires.
They can be more randomized materials.
But one of the things that we're
finding a lot is that we're
dealing with very weak moments.
We tend to have to lengthen our experiments to
try and tease out what that FORC signal actually is.
Do you guys have any advice as far
as the pros and cons of
increasing the averaging time versus
running repeat FORCs and then
trying averaging the FORCs together?
What are the pros and cons and what are
the best ways to try and tease
out those magnetic signals that are really there,
but that are just really weak?
Dr. Leonard Spinu: >> What type of level
of magnetic signal are you talking about?
Two hundred micro EMU, 300?
MALE_12: >> This is well written, I'm sure.
Dr. Leonard Spinu: >> VSM limit, is that right?
MALE_12: >> We're getting close to the VSM limit,
and that's an answer to a certain degree.
Dr. Leonard Spinu: >> We're going to use the AGM
because you need to put a smaller mass,
in this case, the single is going
to be even weaker. Yeah.
MALE_11: >> That's right. Then with the AGM,
the question that we often run into
in geology is, is your sample,
because it's so much smaller,
is it actually representative of
the heterogeneity of your sample?
Dr. Leonard Spinu: >> I understand.
MALE_11: >> There's a real desire
to want to try and stay on
the VSM to use a slightly larger sample possible.
Dr. Leonard Spinu: >> For what we did, because we deal
with samples with low signal,
first thing we do, which is easy,
try to increase the average time.
Sometimes it works, sometimes doesn't.
It depends also the level.
Then the second option just mentioned just
to measure the average.
Another thing is,
I don't know other option that we have.
But I think you need to just do more processing.
Manipulation of the data to eliminate the noise.
MALE_11: >> The one risk that we sometimes run
into when we slow down
the averaging time considerably as we
get a little bit more drift in the experiment,
of course in the experiment,
that can sometimes cause problems.
But this is something that we do routinely run into.
Dr. Leonard Spinu: What is the mass of
the samples you are using usually?
You are limited physically
on the mass of the samples or the volume or what?
MALE_11: >> The mass of
the samples usually isn't a problem.
The largest that we ever typically get
is one inch diameter cord.
Dr. Leonard Spinu: You put it on the?
MALE_11: >> Yeah.
Dr. Leonard Spinu: It worked? [LAUGHTER]
MALE_11: >> It burns through the vibration motors
usually once
every year and a half or something like that.
We've done that multiple times.
But that is what we need
for earth sciences sometimes. But that's the largest.
Most of the time we're dealing with something that's much
smaller on the order of maybe three millimeters in size.
Dr. Leonard Spinu: >> Any other questions? You go
to watch now and it looks like that.
The FORCs almost finished.
But anyway, I don't have anything special,
just probably try to
answer some of the questions you may have.
But this is the instrument we are doing,
and we were doing FORCs.
As I mentioned, I think for nanowires,
we had this paper in 2004
at Alexander and the collaborator from Ash.
We published, I think, [inaudible] society transaction.
At that time, we didn't have this VSM.
Actually, we used, I think,
the previous Lakeshore VSM,
and it took obviously more time and what we did,
we still process, I think,
with forking as you know, process other software.
But we also did FORCs with the squid, and actually,
we get a different data type format,
and obviously take also longer time.
We also had all these ways
to manipulate the data and such a way to put it,
for example, in the right format for FORC.
Now, what is probably not known,
but when you put all parameters to
be on the software to get the FORCs,
those appears on the header of the data file.
Actually, these are used by FORC actually to process.
Whatever put HB_1,
HB_2 or AC_1,
AC_2, these actually a number of FORCs.
Actually, these are looking
for when you load the data file and the FORC nail.
That's why if you
use a different data format or the header,
it's not there, you may have some issues.
Any questions? Josh,
I don't have any other thing special for that.
I planned this to do it,
but more interactive with.
We can try to wait. I don't know, how much time is left
there? Thirty two minutes.
Anyway, this is what is taking care of taking the data,
I don't know why.
I'd be glad to answer other questions.
Other FORC that actually is done,
and we did not mention it,
actually, this will be interesting.
I don't know, maybe talk about this.
Actually this was one idea we
had when we put together the program.
Try to do, for example, FORCs in temperature,
and I don't know, this was done extensively by Ash group.
You hear, for example, spin crossover compounds,
and you have this spin transition
when we have transition from low spin to high spin.
If you cycle this comeback,
you have those transition,
and you have magnetization
versus temperature hysteresis loops.
You can do temperature-dependent FORCs.
In the case of this sample for spin crossover,
done with the squid.
Obviously, the interpretation of the data is different.
I don't know if Alexander can comment on
this other type of FORCs,
which we do not cover in this workshop.
Alexander: >> Of course, we tried
other types of hysteresis
with this first order reversal curve method.
The obvious extension is the ferroelectric materials.
We did that in parallel with the magnetics.
But it is interesting to study
more complicated hysteresis phenomena
and these spin transition materials
are very special because there are
crystals with molecules with two states,
high spin and low spin.
The molecule has a different volume in each state.
If it's high spin,
the electrons are further to the nucleus
and low spin is near the nucleus.
We have a slight volume change in the molecule.
In the crystal, if one molecule is increasing the volume,
it will be an elastic tension, stress,
and this is the physical way
to explain this hysteresis In these crystals,
you have temperature hysteresis,
but it's a hysteresis that can be changed
by pressure as well and
light because you can illuminate
the material and the molecules
will switch from low spin to high spin.
It's three hysteresis phenomena combined,
and the interactions are purely elastic.
We did the FORC measurements in
temperature and also in pressure.
It's more complicated to experimentally do that to
change the pressure and see the status of your molecules.
With light, it's easier.
We extended this for,
I think it's 10 years now and it's
a standard procedure in spin transition now.
It's a method for solve the reversal curve.
It's used to characterize the temperature hysteresis,
the pressure hysteresis, and light-induced hysteresis.
What I would like to comment on
this measurements is that in such crystals,
the temperature rate is important.
The equivalent here will be the field rate.
In some samples, it's not so important.
In nanowires not important if you-
Dr. Leonard Spinu: Go faster, or slower.
Alexander: Yeah, if you go faster.
But in some samples,
if you change the field rate,
your FORC diagram will change dramatically.
I don't know in geology,
but the time scale is different
there and geologists have large time scale,
so I think it's not so important
because the relaxation times
are spread very widely
because the particles are not selected in any way.
But in magnetism, you can have these nanostructures,
something that have some geometrical parameter,
which can be critical and
the field rate could be essential.
We have measured some samples with
two different field rates
and four diagrams are completely different.
In spin transition,
it's more complicated because for example.
Dr. Leonard Spinu: Capital rate.
Alexander: You have a FORC on the descending branch of
the hysteresis loop and you can have
a FORC from the ascending branch.
Dr. Leonard Spinu: You're going to have different curve.
Alexander: But in temperature hysteresis,
these two are for different temperatures.
Dr. Leonard Spinu: I see.
Alexander: You have different relaxation, it's complicated.
Maybe inmagnetocalorics is the same. Thank you.
Dr. Leonard Spinu: Thank you. Yes, question.
MALE_13: In the current PMC software,
is there a way to do
second order bristle curves
or do you have to program those yourself?
Dr. Leonard Spinu: I guess you can refer this question to
Harry though the answer is no.
MALE_13: The answer is no, you can't do it at all or?
Dr. Leonard Spinu: You can do it, I guess with the field sequences.
I guess you can do it just manually.
You can do anything.
You can put any sequence of fields.
Alexander: We have measured second order reversal curves.
Dr. Leonard Spinu: SORC.
Alexander: SORC, yeah. [LAUGHTER] It's
a lot of time to do it.
[LAUGHTER]
Dr. Leonard Spinu: The third order form.
Alexander: But from the theoretical point of view,
it's important to say that if you compare
FORC diagram like a tool to find interactions,
and the previous methods
like Henkel plot or Delta M plot,
this Delta M plot is a second order measurement.
We compare that and we
established the link between the Delta M. It's
a special case of
second order because the measurements are remnant in
zero field and maybe also in angiology.
These measurements are used.
But second order curves can be measured and can
provide interesting information
for the reversible component.
[inaudible] also measured such second order.
Dr. Leonard Spinu: Any question, comments?
About FORCs or anybody else measure first
or reversal curves in
any interesting compounds can
share from their experience, I don't know.
Alexander: Maybe another topic would be if
this saturation is not attained and it's
not first order, it's higher order.
But you don't know what happens
if you don't saturate
exactly the sample and you cut a region.
Is that exactly the region
as in the FORC or is shifted or?
Dr. Leonard Spinu: Actually, you can do partial if you have,
for example, soft hard
material or you have coupled material.
Sometime you can use partially.
It is to just pinpoint, let's say,
to hard face, you just do
higher fields and higher fields FORCs.
Alexander: These are not exactly
the first order or something. Yeah.
Dr. Leonard Spinu: Well, you can do first order reversal curve.
Alexander: Even in exchange bias it's difficult to
define if it's first order or not.
Dr. Leonard Spinu: Yes.
MALE_14: I guess this is a question of
Alexander and others who have measured SORCs.
Is there any difference between
the second order reversal curve
and the first order reversal curves?
Obviously, in an exchange bias system, there would be,
but if it's not an exchange bias system,
is there any difference?
Alexander: Ideally, there shouldn't be
any difference
between the first order reversal curve diagram
and second order reversal curve diagram.
But experimentally, there are
differences and differences are
coming from the reversible component.
We use second order in zero field.
Go measure the FORC and then go to zero.
This is a special second order reversal curve,
the remnant second order reversal curve.
In this case, when you measure in zero field,
you expect a lower value for the reversible component.
If you compare the first order
and the second order, in fact,
you compare the system with
the reversible component and
without the reversible component.
I know the reversible component is
very debatable at this moment and probably
the next FORC conference should
be on reversible and on kinetic effects and so on.
If you have a reversible component
and you have a mean field,
the reversible will be connected with the irreversible.
You have a reversible component
spread into the irreversible.
That's what you see,
comparing the first and second order diagrams.
MALE_13: I was just wondering how long that measurement
takes to do the remnant SORC.
MALE_15: [inaudible]
Dr. Leonard Spinu: Yeah.
Alexander: Really, Joe Davis has
measured SORC on spring magnets,
and our motivation at the time was
that using FORC we can
study when the soft and holly start reversing.
Then what SORC can tell you is what happens when
the hard layer already
started reversing. Partially reverse.
Then SORC allow us to locally probe
the reversal characteristics of the bilayer system.
We can learn a lot more about
the switching and
the exchange coupling between the layers.
From there, we can actually extract a lot of
information about the exchange
coupling within the system.
It does take a lot longer, right, Joe?
You have any other things you want to ship?
Joe Davis: Sorry, I was just pulling up my poster
from 2006 on this work.
The big thing, I think,
we see with the SORC measurements,
at least in the exchange spring system,
as Kai was mentioning,
is how when that hard layer starts to reverse,
you really start to affect
the interaction landscape of the soft layer.
You see, when you
partially go down one of these hard layer loops,
and then you take a SORC measurement,
you do get a distinctly different FORC pattern.
It's only when you get out back close to
saturation that you return to the,
I guess I would say reflected
FORC distribution if you keep everything in
the same scheme and are moving back and forth.
There's a lot it can tell you
about these interaction things.
I think exchange bias systems
are particularly interesting because
there's a definite reversal asymmetry.
As Bob was giving a lovely talk the other day at NVE,
one direction can be
controlled through magnetostatics interactions,
and the other can be controlled through exchange
coupling one way or another.
There's a lot of fascinating reversal phenomena
that the SORCs really reveal.
I'm waiting for some torque curves here too.
[LAUGHTER] We could go all day. Anyhow.
Dr. Leonard Spinu: We have a problem. Well, we have
fourth order going to be
FORC again or be [OVERLAPPING] [LAUGHTER]
Joe Davis: I think at some point,
we need to start talking to the Lakeshore guys.
We need a better system for higher order reversal curves.
Dr. Leonard Spinu: Anyway, it looks like
the measurement is finished.
What I will do at this point,
I will take the data file on my laptop and then
I'm going to email it to Rich
and hopefully going to see something come out.
The Forendo, I don't know,
is anybody else question regarding
the measurements or the way we're doing
the measurements or just tell my students
that is okay? Question.
MALE_15: Discrete versus continuous.
Dr. Leonard Spinu: To do what?
MALE_15: Discrete versus continuous.
Dr. Leonard Spinu: Danny, a question here
from audience, I don't know if you hear me.
One second. Do you hear us, Danny?
Danny: Yeah. He was asking,
did I do discrete versus continuous?
Dr. Leonard Spinu: Yes.
Danny: For this particular one,
we can find out really quick.
I use continues to make it quicker.
Dr. Leonard Spinu: Continue to make it quicker if
we're going to be a little bit more noise.
Danny: [inaudible] the time just a little bit.
Dr. Leonard Spinu: Thank you. Now, at this point,
I will just try to get the data file.
Then if there are
no other questions regarding the measurement,
I just close the Skype connection
and I'm going to leave the Team Viewer.
Alexander: Leonard.
Dr. Leonard Spinu: Yes.
Alexander: Just one quick thing on
selecting the measurement parameters.
Just my way of going about it is a very,
in calculus and as it was shown yesterday,
I think Victorino showed it,
integrating over a curve, you draw a big rectangle.
It's a very good exercise in
a very rudimentary prisec model
for you can fill
little squares in and you have to estimate,
well, near saturation you're going to have
a little bit of bias and a little bit of coercivity.
You go further out, and that can
really help find your landscape pretty quickly.
Just in terms of the width of the loops
and where things truncate and stuff.
Dr. Leonard Spinu: Thanks. Let's take the data file.
Let's see, I need to use.
Danny and Daniel, I think I go to close for now.
I'm going to take the data file from it.
If I need any help,
I probably call you and try to reconnect.
Just go to close Skype.
Let's go here, File Transfer.
Let's see. This is local, this is remote.
Danny: The files on the desktop.
Dr. Leonard Spinu: What's the name?
Danny: It says FORC_FOR_Pres. Then that's the date.
Dr. Leonard Spinu: I put on my desktop. Transfer.
Danny: Hopefully it works.
Dr. Leonard Spinu: I think like this. Any questions?
No?
Let me close the Skype here altogether.
I guess so. Then the question,
we can just continue
discussing if you have probably a longer break now.
[APPLAUSE]