arXiv subjects

Alexander Samardak

Publications and source records attributed to Alexander Samardak.

4 recordsLinked to original sources

arXiv2024

Spin-Orbit Torque-Assisted Detection of the Canted Magnetization Phase in a CoTb-Based Ferrimagnet

Ferrimagnets have the potential to play a key role in spintronics due to their high stability, low energy consumption, and rapid magnetic state switching. These characteristics are typically observed in ferrimagnetic materials near magnetic or angular compensation states. Near the magnetic compensation point, an external field can disrupt the collinearity between the sublattices, leading to aligned magnetic projections. In this work, a violation of antiferromagnetic ordering is detected by a change in the direction of the effective field induced by spin-orbit torque, without altering the dominance type. In the studied W-Co70Tb30-Ru structure, the canted phase region is observed near room temperature under external fields of approximately 0.1 T. Using macrospin simulations and analytical derivations, a correlation is established between anisotropy, interlattice exchange interaction, and the presence of the canted phase region.

cond-mat.mtrl-sci↗

arXiv2022

Predicted universality class of step bunching found on DC-heated Si(111) surfaces

Concerted experimental and numerical studies of step bunching on vicinal crystal surfaces resulting from step-down electromigration of partially charged adatoms, confirmed the theoretical prediction of scaling dependence of the minimal bunch distance $l_{\rm min}$ on the bunch size $N$: $l_{\rm min} \sim N^{-\gamma}$, with $\gamma = 2/3$. The value of the so called size-scaling exponent $\gamma$ was observed in experiments on vicinal surfaces of semiconducting, metallic, and dielectric materials. Careful theoretical investigations and numerical calculations predict a second value of $\gamma = 1/2$. However, this value is still not been reported from experiments. And we report here experimental observation of step bunching in the universality class relative to $\gamma = 1/2$. This is achieved by monitoring step flow during sublimation of Si(111)-vicinals heated by a direct step-down current at ~1200$^\circ$C. In the experiment we also measure other characteristic for the bunching quantities, such as the mean total number of steps in the bunch $N$ and the mean bunch width $W$. We then compare our findings with published experimental and numerical data to arrive at a theoretically consistent framework in terms of universality classes. The ultimate benefit of our study is not only to advance fundamental knowledge but also to provide further guidance for bottom-up synthesis of vicinal nanotemplates.

cond-mat.mes-hall↗

arXiv2021

Analyser-free, intensity-based wide-field magneto-optical microscopy

In conventional Kerr- and Faraday microscopy the sample is illuminated with plane-polarised light and a magnetic domain contrast is generated by an analyser making use of the Kerr- or Faraday rotation. In this paper we demonstrate possibilities of analyser-free magneto-optical microscopy based on magnetisation-dependent intensity modulations of the light: (i) The transverse Kerr effect can be applied for in-plane magnetised material, demonstrated for an FeSi sheet. (ii) Illuminating the same sample with circularly polarised light leads to a domain contrast with a different symmetry as the conventional Kerr contrast. (iii) Circular polarisation can also be used for perpendicularly magnetised material, demonstrated for a garnet film and an ultrathin CoFeB film. (iv) Plane-polarised light at a specific angle can be employed for both, in-plane and perpendicular media. (v) Perpendicular light incidence leads to a domain contrast on in-plane materials that is quadratic in the magnetisation and to a domain boundary contrast. (vi) Domain contrast can even be obtained without polariser. In cases (ii) and (iii), the contrast is generated by MCD (Magnetic Circular Dichroism), while MLD (Magnetic Linear Dichroism) is responsible for the contrast in case (v). The domain boundary contrast is due to the magneto-optical gradient effect in metallic samples. A domain boundary contrast can also arise due to interference of phase-shifted magneto-optical amplitudes. An explanation of these contrast phenomena is provided in terms of Maxwell-Fresnel theory.

cond-mat.mtrl-sci↗

arXiv2017

Nanoscale control of perpendicular magnetic anisotropy, interfacial Dzyaloshinskii-Moriya interaction and skyrmions in the inversion-symmetry-broken Ru/Co/W/Ru films

An enhancement of the spin-orbit effects arising on an interface between a ferromagnet (FM) and a heavy metal (HM) is possible through the strong breaking of the structural inversion symmetry in the layered films. Here we show that the introduction of an ultrathin W interlayer between Co and Ru in Ru/Co/Ru films enables to preserve perpendicular magnetic anisotropy (PMA) and simultaneously induce a large interfacial Dzyaloshinskii-Moriya interaction (iDMI). We find that the Ru/Co/W/Ru films have PMA up to 0.35 nm of the nominal thickness of W (tW). The study of the spin-wave propagation in the Damon-Eshbach geometry by Brillouin light scattering (BLS) spectroscopy reveals the drastic increase of the iDMI value with the rising tW. The maximum iDMI of -3.1 erg/cm2 is observed for tW=0.24 nm, which is 10 times larger than the latter for the quasi-symmetrical Ru/Co/Ru films. The ability to simultaneous control the strength of PMA and iDMI in symmetrical HM/FM/HM trilayer systems through the interface engineered inversion asymmetry at the nanoscale excites new fundamental and practical interest to the chiral ferromagnets, which are a potential host for magnetic skyrmions.

cond-mat.mes-hall↗