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Register a new userLongitudinal and transverse magnetoresistance in films with tilted out-of-plane magnetic anisotropy
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Tilted off-plane magnetic anisotropy induces two unusual characteristic magnetotransport phenomena: extraordinary Hall effect in the presence of an in-plane magnetic field, and non-monotonic anisotropic magnetoresistance in the presence of a field normal to the sample plane. We show experimentally that these effects are generic, appearing in multiple ferromagnetic systems with tilted anisotropy introduced either by oblique deposition from a single source or in binary systems co-deposited from separate sources. We present a theoretical model demonstrating that these observations are natural results of the standard extraordinary Hall effect and anisotropic magnetoresistance, when the titled anisotropy is properly accounted for. Such a scenario may help explaining various previous intriguing measurements by other groups.
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Permalloy (Py:Ni81Fe19) exhibits an anisotropic magnetoresistance (AMR) which is very often used to read magnetic signals from storage devices. Py-films of thickness 20nm were prepared by dc-magnetron sputtering in a magnetic field onto thermally oxidized Si-wafers and annealed ex situ at temperatures up to 1000K in order to investigate the dependence of the magnetic anisotropy and the AMR on heat treatments. The films exhibit an uniaxial anisotropy after preparation which changes during annealing above 520K. The AMR along the former magnetically easy axis as well as the corresponding field sensitivity are increased by a heat treatment around 700K reaching maxima of about 8% and a maximum sensitivity of 1.5%/Oe, respectively. We discuss possible sources for the change in anisotropy, i.e. strain effects, inhomogeneities, and changes of the local atomic order.
Structural, electronic and magnetic properties of bulk ilmenite CoTiO$_3$ are analyzed in the framework of Density Functional Theory (DFT), using the Generalized Gradient Approximation (GGA) and Hubbard-corrected approaches. We find that the G-type antiferromagnetic (G-AFM) structure, which consists of antiferromagnetically coupled ferromagnetic $ab$ planes, is the ground-state of the system, in agreement with experiments. Furthermore, cobalt titanates present two critical temperatures related to the breaking of the inter- and intra-layer magnetic ordering. This would result in the individual planes remaining ferromagnetic even at temperatures above the Neel temperature. When spin-orbit coupling is included in our calculations, we find an out-of-plane magnetic anisotropy, which can be converted to an in-plane anisotropy with a small doping of electrons corresponding to about 2.5% Ti substitution for Co, consistent with experimental expectations. We thus present a disorder-dependent study of the magnetic anisotropy in bulk $text{CoTiO}_3$, which will determine its magnon properties, including topological aspects.
We demonstrate that chiral skyrmionic magnetization configurations can be found as the minimum energy state in B20 thin film materials with easy-plane magnetocrystalline anisotropy with an applied magnetic field perpendicular to the film plane. Our observations contradict results from prior analytical work, but are compatible with recent experimental investigations. The size of the observed skyrmions increases with the easy-plane magnetocrystalline anisotropy. We use a full micromagnetic model including demagnetization and a three-dimensional geometry to find local energy minimum (metastable) magnetization configurations using numerical damped time integration. We explore the phase space of the system and start simulations from a variety of initial magnetization configurations to present a systematic overview of anisotropy and magnetic field parameters for which skyrmions are metastable and global energy minimum (stable) states.
Describing the origin of uniaxial magnetic anisotropy (UMA) is generally problematic in systems other than single crystals. We demonstrate an in-plane UMA in amorphous CoFeB films on GaAs(001) which has the expected symmetry of the interface anisotropy in ferromagnetic films on GaAs(001), but strength which is independent of, rather than in inverse proportion to, the film thickness. We show that this volume UMA is consistent with a bond-orientational anisotropy, which propagates the interface-induced UMA through the thickness of the amorphous film. It is explained how, in general, this mechanism may describe the origin of in-plane UMAs in amorphous ferromagnetic films.
Phase-separated semiconductors containing magnetic nanostructures are relevant systems for the realization of high-density recording media. Here, the controlled strain engineering of Ga$delta$FeN layers with Fe$_y$N embedded nanocrystals (NCs) textit{via} Al$_x$Ga$_{1-x}$N buffers with different Al concentration $0<x_mathrm{Al}<41$% is presented. Through the addition of Al to the buffer, the formation of predominantly prolate-shaped $varepsilon$-Fe$_3$N NCs takes place. Already at an Al concentration $x_mathrm{Al}$,$approx$,5% the structural properties---phase, shape, orientation---as well as the spatial distribution of the embedded NCs are modified in comparison to those grown on a GaN buffer. Although the magnetic easy axis of the cubic $gamma$-Ga$_y$Fe$_{4-y}$N nanocrystals in the layer on the $x_mathrm{Al} = 0%$ buffer lies in-plane, the easy axis of the $varepsilon$-Fe$_3$N NCs in all samples with Al$_x$Ga$_{1-x}$N buffers coincides with the $[0001]$ growth direction, leading to a sizeable out-of-plane magnetic anisotropy and opening wide perspectives for perpendicular recording based on nitride-based magnetic nanocrystals.
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