High tunnel magnetoresistance and magnetism in metastable bcc Co${}_{1-x}$Mn${}_x$-based magnetic tunnel junctions

Abstract

Co-rich Co${}_{1-x}$Mn${}_x$ alloys have hcp or fcc disordered phases and those ferromagnetic orderings are significantly deteriorated with increasing Mn concentration $x$ in bulk. On the other hand, those metastable bcc phases show properties attractive to spintronics, e.g., high tunnel magnetoresistance (TMR) ratio of more than 200% (600%) at 300 K (10 K) in magnetic tunnel junctions (MTJs) with the $x$ = 0.25 bcc alloy electrodes [Kunimatsu et al., Appl. Phys. Express 13, 083007 (2020)]. Here, we report systematic study of structure and magnetism for epitaxial thin films as well as the TMR effect in MgO(001)-barrier MTJs with electrodes comprising those bcc films. The single phase bcc Co${}_{1-x}$Mn${}_x$(001) films were pseudomorphically grown on Cr(001) for 0.14 < $x$ < 0.50 with a sputtering technique. The magnetization was larger than that of pure Co for $x$ = 0.14-0.25 and deceased with further increasing $x$. This behavior mainly stemmed from the composition dependence of magnetic moment of Mn that exceeded 2 ${\mu }_B$ at the maximum, unveiled by X-ray magnetic circular dichroism. Correspondingly, within the range of 0.25 < $x$ < 0.37, the TMR ratio decreased from 620% (229%) to 450% (194%) at 10 K (300 K) as $x$ increased. We discussed the relationship between the magnetism and high TMR ratio with different $x$ with the aid of the ab-initio band structure calculations.

21 pages, 10 figures

References in corpus (1)

• Large magnetoresistance in bcc Co/MgO/Co and FeCo/MgO/FeCo tunneling junctions

Cited by in corpus (1)

• Lattice Softening in Metastable bcc CoxMn100-x(001) Ferromagnetic Layers for a Strain-Less Magnetic Tunnel Junction