Computational Studies on Magnetic Information Storage Devices and Systems

Abstract

Micromagnetics and information technology, combined, has emerged as a flourishing field in the area of digital data management. In order to explore new ideas in a flourishing field, computational studies are essential alongside experimental implementations. In this thesis, some of the physics-based computational techniques have been utilized to investigate underlying principles, propose new design, and compare different technologies, in the area of applied magnetism. Most of the computations have been performed on the micromagnetic simulation platform. Readily available commercial CAD tools in the area of magnetism/spintronics are not customizable enough to study specific physical phenomena, with insightful details. Magnetism related phenomena, being originated from quantum mechanics, cannot be analyzed accurately with classical/SPICE models. Hence, most of the studies in this thesis were performed using self-developed/customized physics-based simulation frameworks. Over the course of time, the thesis has branched into three different projects. In the first project, the effectiveness of voltage assisted switching in a large-area magnetic tunnel junction (MTJ) has been explained. More specifically, micromagnetic simulation has been performed to investigate the possible reason behind the observed large change in the switching field with applied voltage in experimental MTJs. It has been found that the film roughness plays a significant role in boosting the intrinsic effect of an applied electric field in experimental devices, with dimensions in the sub-micron range. The second project of the thesis involved voltage-controlled exchange bias (VCEB) in hetero-structures with magnetoelectric (ME) Cr2O3, and an exchange-coupled ferromagnet (FM). Monte Carlo simulation has been employed to study temperature-dependent magnetic properties of the ME Cr2O3. Using the calculated temperature-dependent properties, exchange bias (EB) mechanism has been explained in a ME Cr2O3/FM system. It has been pointed out that domain formation inside the ME Cr2O3 most probably explains the experimentally observed temperature dependence of the EB. As an extension to the VCEB project, a fully electric-controlled magnetoelectric switching device has been proposed. The proposed device addresses the obvious challenges faced by the traditional ME Cr2O3-based EB switching device. Advantages in terms of scaling, and low electric field operation, have been demonstrated through a developed micromagnetic simulation. The simulation framework is capable of effectively handling a linear ME device in useful dimensions. The thesis ends with a signal-to-noise (SNR)-based comparative study between two most prominent magnetic recording technologies, used in the hard drive. One of them is the perpendicular magnetic recording (PMR), which is the current technology for the shipped hard drives. The other one is the upcoming heat-assisted magnetic recording (HAMR), a soon expected replacement of the current PMR. It has been pointed out that even an unoptimized, bare-minimum heat-assisted magnetic recording (HAMR) design, yields higher SNR than an optimized PMR. SNR comparisons have been calculated for various changes in the head design parameters. The comparisons are expected to increase the motivational drive towards migrating to HAMR from PMR.