arXiv subjects

A. A. Sapozhnik

Publications and source records attributed to A. A. Sapozhnik.

5 recordsLinked to original sources

arXiv2019

Imaging of current induced Néel vector switching in antiferromagnetic Mn$_2$Au

The effects of current induced Néel spin-orbit torques on the antiferromagnetic domain structure of epitaxial Mn$_2$Au thin films were investigated by X-ray magnetic linear dichroism - photoemission electron microscopy (XMLD-PEEM). We observed current induced switching of AFM domains essentially corresponding to morphological features of the samples. Reversible as well as irreversible Néel vector reorientation was obtained in different parts of the samples and the switching of up to 30 % of all domains in the field of view of 10 $μ$m is demonstrated. Our direct microscopical observations are compared to and fully consistent with anisotropic magnetoresistance effects previously attributed to current induced Néel vector switching in Mn$_2$Au.

cond-mat.mtrl-sci↗

arXiv2018

Experimental determination of exchange constants in antiferromagnetic Mn$_2$Au

Mn$_2$Au is an important antiferromagnetic (AF) material for spintronics applications. Due to its very high Néel temperature of about 1500 K, some of the basic properties are difficult to explore, such as the AF susceptibility and the exchange constants. Experimental determination of these properties is further complicated in thin films by unavoidable presence of uncompensated and quasiloose spins on antisites and at interfaces. Using x-ray magnetic circular dichroism (XMCD), we have measured the spin and orbital contribution to the susceptibility in the direction perpendicular to the in-plane magnetic moments of a Mn$_2$Au(001) film and in fields up to 8 T. By performing these measurements at a low temperature of 7 K and at room temperature, we were able to separate the loose spin contribution from the susceptibility of AF coupled spins. The value of the AF exchange constant obtained with this method for a 10 nm thick Mn$_2$Au(001) film equals to (24 $\pm$ 5) meV.

cond-mat.mtrl-sci↗

arXiv2018

Direct imaging of antiferromagnetic domains in Mn$_2$Au manipulated by high magnetic fields

In the field of antiferromagnetic (AFM) spintronics, information about the Néel vector, AFM domain sizes, and spin-flop fields is a prerequisite for device applications but is not available easily. We have investigated AFM domains and spin-flop induced changes of domain patterns in Mn2Au(001) epitaxial thin films by X-ray magnetic linear dichroism photoemission electron microscopy (XMLD-PEEM) using magnetic fields up to 70 T. As-prepared Mn$_2$Au films exhibit AFM domains with an average size $\sim$ 1 $μ$m. Application of a 30T field, exceeding the spin-flop field, along a magnetocrystalline easy axis, dramatically increases the AFM domain size with Néel vectors perpendicular to the applied field direction. The width of Néel type domain walls (DW) is below the spatial resolution of the PEEM and therefore can only be estimated from an analysis of the DW profile to be smaller than 80 nm. Furthermore, using the values for the DW width and the spin-flop field, we evaluate an in-plane anisotropy constant ranging between 1 and 17 $μ$eV/f.u.

cond-mat.mtrl-sci↗

arXiv2018

Néel Spin Orbit Torque driven antiferromagnetic resonance in Mn$_{2}$Au probed by time-domain THz spectroscopy

We observe the excitation of collective modes in the THz range driven by the recently discovered Néel spin-orbit torques (NSOT) in the metallic antiferromagnet Mn$_{2}$Au. Temperature dependent THz spectroscopy reveals a strong absorption mode centered near 1 THz, which upon heating from 4 K to 450 K softens and looses intensity. Comparison with the estimated eigenmode frequencies implies that the observed mode is an in-plane antiferromagnetic resonance (AFMR) mode. The AFMR absorption strength exceeds those found in antiferromagnetic insulators, driven by the magnetic field of the THz radiation, by three orders of magnitude. Based on this and the agreement with our theory modelling, we infer that the driving mechanism for the observed mode is the current induced NSOT. This electric manipulation of the Neél order parameter at high frequencies makes Mn$_{2}$Au a prime candidate for AFM ultrafast memory applications.

cond-mat.str-el↗

arXiv2017

Writing and Reading antiferromagnetic Mn$_2$Au: Néel spin-orbit torques and large anisotropic magnetoresistance

Antiferromagnets are magnetically ordered materials which exhibit no net moment and thus are insensitive to magnetic fields. Antiferromagnetic spintronics aims to take advantage of this insensitivity for enhanced stability, while at the same time active manipulation up to the natural THz dynamic speeds of antiferromagnets is possible, thus combining exceptional storage density and ultra-fast switching. However, the active manipulation and read-out of the Néel vector (staggered moment) orientation is challenging. Recent predictions have opened up a path based on a new spin-orbit torque, which couples directly to the Néel order parameter. This Néel spin-orbit torque was first experimentally demonstrated in a pioneering work using semimetallic CuMnAs. Here we demonstrate for Mn$_2$Au, a good conductor with a high ordering temperature suitable for applications, reliable and reproducible switching using current pulses and readout by magnetoresistance measurements. The symmetry of the torques agrees with theoretical predictions and a large read-out magnetoresistance effect of more than $\simeq 6$~$\%$ is reproduced by ab initio transport calculations.

cond-mat.mtrl-sci↗