Giant magnetic anisotropy of the bulk antiferromagnets IrMn andIrMn3from first principles (original) (raw)
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Anisotropy in antiferromagnets
Journal of Applied Physics, 2020
Due to the advent of antiferromagnetic (AF) spintronics, there is a burgeoning interest in AF materials for a wide range of potential and actual applications. Generally, AFs are characterized via the ordering at the Néel temperature (TN), but to have a stable AF configuration, it is necessary that the material has a sufficient level of anisotropy so as to maintain the orientation of the given magnetic state fixed in one direction. Unlike the case for ferromagnets, there are little established data on the anisotropy of AFs and, in particular, its origins, other than it being magneto-crystalline, and those factors which control it. In this perspective article, these factors are reviewed in light of recent and established experimental data. The anisotropy can be found indirectly via the exchange bias phenomenon. This technique is reviewed and, in particular, the implications for the nature of the anisotropy that is measured and its distribution. Finally, a strategy is proposed that wou...
Isothermal anisotropic magnetoresistance in antiferromagnetic metallic IrMn
Scientific reports, 2016
Antiferromagnetic spintronics is an emerging field; antiferromagnets can improve the functionalities of ferromagnets with higher response times, and having the information shielded against external magnetic field. Moreover, a large list of aniferromagnetic semiconductors and metals with Néel temperatures above room temperature exists. In the present manuscript, we persevere in the quest for the limits of how large can anisotropic magnetoresistance be in antiferromagnetic materials with very large spin-orbit coupling. We selected IrMn as a prime example of first-class moment (Mn) and spin-orbit (Ir) combination. Isothermal magnetotransport measurements in an antiferromagnetic-metal(IrMn)/ferromagnetic-insulator thin film bilayer have been performed. The metal/insulator structure with magnetic coupling between both layers allows the measurement of the modulation of the transport properties exclusively in the antiferromagnetic layer. Anisotropic magnetoresistance as large as 0.15% has ...
Magnetic anisotropy of antiferromagnetic RbMnF3
RbMnF 3 is known to have a very small magnetic anisotropy and to be a nearly ideal realization of a threedimensional Heisenberg antiferromagnet. Although its critical behavior has been studied in detail, the origin of the residual magnetic anisotropy has not had sufficient attention. Here we present an experimental investigation of the temperature dependence of the anisotropy in RbMnF 3 and show that it can be explained by a model for the crystal field. The experimental data are obtained with magnetization and susceptibility measurements from which we can accurately obtain the critical magnetic field for the transition from the antiferromagnetic to the spin-flop phase. The fit of the theoretical model to the data yields information on some microscopic parameters.
The antiferromagnetic structures of IrMn3 and their influence on exchange-bias
Scientific Reports, 2013
We have determined the magnetic structures of single-crystal thin-films of IrMn 3 for the crystallographic phases of chemically-ordered L1 2 , and for chemically-disordered face-centred-cubic, which is the phase typically chosen for information-storage devices. For the chemically-ordered L1 2 thin-film, we find the same triangular magnetic structure as reported for the bulk material. We determine the magnetic structure of the chemically-disordered face-centred-cubic alloy for the first time, which differs from theoretical predictions, with magnetic moments tilted away from the crystal diagonals towards the face-planes. We study the influence of these two antiferromagnetic structures on the exchange-bias properties of an epitaxial body-centred-cubic Fe layer showing that magnetization reversal mechanism and bias-field in the ferromagnetic layer is altered significantly. We report a change of reversal mechanism from in-plane nucleation of 906 domain-walls when coupled to the newly reported cubic structure towards a rotational process, including an out-of-plane magnetization component when coupled to the L1 2 triangular structure.
2018
Exchange interactions up to fourth nearest neighbor are shown within a classical local-moment Heisenberg approach to be important to model inelastic neutron scattering data on the fcc kagome antiferromagnet IrMn$_3$. Spin wave frequencies are calculated using the torque equation and the magnetic scattering function, S(bfQ,omega)S({\bf Q},\omega)S(bfQ,omega), is determined by a Green's function method, as an extension of our previous work, LeBlanc et al, Phys. Rev. B 90, 144403 (2014). Results are compared with intensity contour data on powder samples of ordered IrMn$_3$, where magnetic Mn ions occupy lattice sites of ABC stacked kagome planes. Values of exchange parameters taken from DFT calculations used in our model provide good agreement with the experimental results only if further-neighbor exchange is included. Estimates of the observed energy gap support the existence of strong cubic anisotropy predicted by DFT calculations.
Physical Review B, 2011
The magnetic anisotropy energy (MAE) and element-specific contributions to the MAE have been studied for Mn-based antiferromagnetic alloys with layered L1 0 structure within the framework of the local spin-density approximation and the fully relativistic torque method. It is found that the contribution to the total MAE from nonmagnetic 3d and 4d elements in MnNi and MnPd alloys are comparable to the contribution of the magnetic Mn atoms. In the 3d-5d MnIr and the 4d-5d MnRh alloys the Ir and Rh contributions are found to be dominating. The origin of this nonzero contribution into the MAE from the atom with zero spin moment is linked to the nontrivial atomic spin density distribution, which gives a zero moment only on average. We also find and discuss the strong dependence of the total and element-specific contributions to the MAE on the state of magnetic order.
Anisotropic magnetic fluctuations in 3- antiferromagnets
Journal of Magnetism and Magnetic Materials, 2007
The anisotropy of magnetic fluctuations propagating along the high-symmetry directions in cubic systems with 3-k magnetic order is analyzed within the random-phase approximation assuming anisotropic exchange interactions. Both transverse and longitudinal structures are considered, with reference to the UO 2 and USb compounds, respectively. In the case of UO 2 , the spin-waves polarizations calculated for acoustic and optical branches are favorably compared with three-dimensional polarization analysis experiments carried out on a triple axis spectrometer. The overall spin-waves polarization behavior emerges as a consequence of the 3-k nature of the magnetic order, whatever the strength of the exchange coupling assumed. r
Science advances, 2016
There has been considerable interest in spin-orbit torques for the purpose of manipulating the magnetization of ferromagnetic elements for spintronic technologies. Spin-orbit torques are derived from spin currents created from charge currents in materials with significant spin-orbit coupling that propagate into an adjacent ferromagnetic material. A key challenge is to identify materials that exhibit large spin Hall angles, that is, efficient charge-to-spin current conversion. Using spin torque ferromagnetic resonance, we report the observation of a giant spin Hall angle [Formula: see text] of up to ~0.35 in (001)-oriented single-crystalline antiferromagnetic IrMn3 thin films, coupled to ferromagnetic permalloy layers, and a [Formula: see text] that is about three times smaller in (111)-oriented films. For (001)-oriented samples, we show that the magnitude of [Formula: see text] can be significantly changed by manipulating the populations of various antiferromagnetic domains through ...
Spin-Flipping Associated With the Antiferromagnet IrMn
IEEE Transactions on Magnetics, 2000
We have used current-perpendicular-to-plane magnetoresistance measurements of Py-based exchange-biased spin-valves containing IrMn inserts of thickness to estimate the spin-flipping probability of the antiferromagnet IrMn. From = 0 to = 1 nm, we find a rapid decrease in 1 = ( ), by about a factor of 50-here is the area through which the CPP current flows, and and are the resistances with the moments of the two Py layers oriented anti-parallel (AP) or parallel (P) to each other. We attribute this decrease to very strong spin-flipping in the IrMn/Cu interfacial region, with effective spin diffusion length IrMn Cu sf = 0.24 nm, only about 1 monolayer (ML). But for from 2 to 5 nm, the decrease of 1 with increasing IrMn thickness is much slower.