Manipulating Spin-Orbit Coupling Effects

By Andy Massey on August 2, 2017

In thermal equilibrium the solubility of interstitial Boron in bcc Fe-Co does not exceed 0.1 atomic percent (at.%), but the solubility limit can be significantly increased using non-equilibrium preparation methods such as pulsed laser deposition (PLD). In a recent paper published in Journal of Physics: Condensed Matter, Salikhov et al. use PLD to deposit Fe-Co and achieve doping levels of up to 4 at.% of interstitial B. These films are tetragonally distorted and show improved magnetic properties due to the influence of spin-orbit coupling. Hear more from the authors about their research below:

Tetragonal distortion yields large magnetocrystalline anisotropy energy (MAE), which is an important consideration when designing materials for permanent magnets. Furthermore, we identify an enhanced influence of spin-orbit coupling (SOC) as seen from the increased orbital magnetic moment and spectroscopic splitting (g-) factor compared to cubic and un-doped Fe-Co. These results are essential to understand the influence of SOC on the magnetic properties of the alloys, which are crucial for applications in spintronic devices, logic systems and tunneling magnetoresistance elements, where Fe-Co and Fe-Co-B alloys are widely used. We also show that the magnetic damping parameter decreases with increasing B concentration, making these materials attractive for magnonics applications. The figure below summarizes some of the main results of our study.

a) Tetragonal distortion quantified by the c/a ratio of lattice constants (black circles and left scale bar) of 20 nm thick Fe-Co-B films prepared by PLD with different B concentrations. The g-factor, which represents the admixture of orbital moment to the total magnetic moment (blue squares and right outer scale bar), follows the c/a ratio indicating that reduced crystal symmetry and interstitial B leads to an enhancement of the effect of SOC in the Fe-Co-B. The out-of-plane MAE (red triangles and right inner scale bar) is highest at largest c/a: however, it nearly vanishes at 10 at.% B, showing the strong influence of the film microstructure on MAE. b) This influence can be seen from the correlation of the in-plane MAE of Fe-Co-B films (blue squares and right outer scale bar) with the decrease of crystallite size determined from x-ray diffraction (black circles and left scale bar). Since the MAE decreases with decreasing grain size, the coercive field of magnetic hysteresis loops measured along the in-plane Fe-Co [110] easy axis also decreases as seen in the figure (red triangles and right inner scale bar). Figure adapted from J. Phys.: Condens. Matter 29 275802 © Copyright 2017 IOP Publishing.

About the authors

This work is a collaborative research work between the group of Professor Michael Farle from University of Duisburg-Essen, group of Dr. Sebastian Fähler from IFW Dresden, group of Professor Olle Eriksson from Uppsala University and Dr. Radu Abrudan from Helmholtz-Zentrum-Berlin. The work has been performed within the European Community’s Seventh Framework Programme No. 280670 REFREEPERMAG.

This work is licensed under a Creative Commons Attribution 3.0 Unported License