arXiv subjects

Mark Gubbins

Publications and source records attributed to Mark Gubbins.

3 recordsLinked to original sources

arXiv2025

Laser-Induced Current Transients in Ultrafast All-Optical Switching of Metallic Spin Valves

All-optical switching in a ferromagnetic spin valve is studied here using atomistic spin drift-diffusion dynamics, which includes contributions from spin pumping and superdiffusive transport. We find the switching is governed principally by spin-polarized currents due to non-equilibrium hot electrons excited by the laser pulse and re-equilibration currents. In particular, an initial superdiffusive forward flow of electrons, polarized by the free layer, is generated. This drives parallel to antiparallel switching of the free layer through accumulation of minority spins at the reference layer. A diffusive backward flow of electrons, repolarized by the reference layer, follows the initial superdiffusive flow as the charge distribution re-equilibrates. Due to the pulse width-dependent asymmetric amplitudes of the forward and backward transients, the latter can drive antiparallel to parallel switching, and create multi-domain structures at higher laser fluences and longer pulses. The results obtained here are in agreement with experimental observations, providing a framework for self-consistent modelling of all-optical switching in metallic heterostructures.

cond-mat.mes-hall↗

arXiv2025

Multiscale micromagnetic / atomistic modeling of heat assisted magnetic recording

Heat-assisted magnetic recording (HAMR) is a recent advancement in magnetic recording, allowing to significantly increase the areal density capability (ADC) of hard disk drives (HDDs) compared to the perpendicular magnetic recording (PMR) technology. This is enabled by high anisotropy FePt media, which needs to be heated through its Curie temperature ($T_C$) to facilitate magnetization reversal by an electromagnetic write pole. HAMR micromagnetic modeling is therefore challenging, as it needs to be performed in proximity to and above $T_C$, where a ferromagnet has no spontaneous magnetization. An atomistic model is an optimal solution here, as it doesn't require any parameter renormalization or non-physical assumptions for modeling at any temperature. However, a full track atomistic recording model is extremely computationally expensive. Here we demonstrate a true multiscale HAMR modeling approach, combining atomistic spin dynamics modeling for high temperature regions and micromagnetic modeling for lower temperature regions, in a moving simulation window embedded within a long magnetic track. The advantages of this approach include natural emergence of $T_C$ and anisotropy distributions of FePt grains. Efficient GPU optimization of the code provides very fast running times, with a 60~nm wide track of twenty-five 20~nm - long bits being recorded in several hours on a single GPU. The effects of realistic FePt L$_{10}$ vs simple cubic crystal structure is discussed, with the latter providing further running time gains while keeping the advantages of the multiscale approach.

cond-mat.mtrl-sci↗

arXiv2017

Transition Jitter in Heat Assisted Magnetic Recording by Micromagnetic Simulation

In this paper we apply an extended Landau-Lifschitz equation, as introduced by Baňas et al. for the simulation of heat-assisted magnetic recording. This equation has similarities with the Landau-Lifshitz-Bloch equation. The Baňas equation is supposed to be used in a continuum setting with sub-grain discretization by the finite-element method. Thus, local geometric features and nonuniform magnetic states during switching are taken into account. We implement the Baňas model and test its capability for predicting the recording performance in a realistic recording scenario. By performing recording simulations on 100 media slabs with randomized granular structure and consecutive read back calculation, the write position shift and transition jitter for bit lengths of 10nm, 12nm, and 20nm are calculated.

physics.comp-ph↗