Structural and magnetic properties and tunnel magnetoresistance for Co₂(Cr,Fe)Al and Co₂FeSi full-Heusler alloys

Abstract

We have investigated the structure and magnetization of Co2(Cr1−xFex)Al (0 ⩽ x ⩽ 1) and Co2FeSi full-Heusler alloy films deposited on thermally oxidized Si (SiO2) and MgO (001) single crystal substrates by ultra-high vacuum sputtering at various temperatures. The films were also post-annealed after deposition at room temperature (RT). Magnetic tunnel junctions with a full-Huesler alloy electrode were fabricated with a stacking structure of Co2YZ (20 nm)/Al (1.2 nm)-oxide/Co75Fe25 (3 nm)/IrMn (15 nm)/Ta (60 nm) and microfabricated using electron beam lithography and Ar ion etching with a 102 µm2 junction area, where Co2YZ stands for Co2(Cr1−xFex)Al or Co2FeSi. The tunnel barriers were formed by the deposition of 1.2 nm Al, followed by plasma oxidization in the chamber. The x-ray diffraction revealed the A2 or B2 structure depending on heat treatment conditions and the substrate, but not L21 structure for the Co2(Cr1−xFex)Al (0 ⩽ x ⩽ 1) films. The L21 structure, however, was obtained for the Co2FeSi films when deposited on a MgO (001) substrate at elevated temperatures above 473 K. The maximum tunnelling magnetoresistance (TMR) was obtained with 52% at RT and 83% at 5 K for a junction using a Co2(Cr0.4Fe0.6)Al electrode. While the junction using a Co2FeSi electrode with the L21 structure exhibited the TMR of 41% at RT and 60% at 5 K, which may be improved by using a buffer layer for reducing the lattice misfit between the Co2FeSi and MgO (001) substrate.

59Co nuclear magnetic resonance study of the local distribution of atoms in the Heusler compound Co2FeAl0.5Si0.5

“…17,18 The quite large 59 Co NMR, corresponding distribution of Fe and (8 -k)Z þ kZ 0 in the first coordination shell of the 59 Co nuclei, the resonance frequencies, and the corresponding hyperfine fields H hf .…”

Antiferromagnetic dipolar ordering in[Co2MnGe∕V]Nmultilayers

“…For the newly predicted half-metal Co 2 Cr 0.6 Fe 0.4 Al as magnetic electrode a TMR ratio of 74% at 55 K was found, using a MgO tunneling barrier [68,69,67]. The maximum TMR values obtained for an Al oxide barrier are 52% at RT and 83% at 5 K [70]. The spin polarization was found to be 81% [71].…”

“…Smaller values for the TMR ratio were obtained in junctions using a Co 2 FeSi electrode, i.e. 41% at RT and 60% at 5 K [70].…”

Magnetic anisotropies and magnetization reversal of the Co2Cr0.6Fe0.4Al Heusler compound

“…4 Fe 0.6 Al/Cu/Co 90 Fe 10 trilayers showed a large giant magnetoresistance of 6.8% at RT, 4 while a tunneling magnetoresistance ratio of 52% at RT and 83% at 5K was reported for the system CCFA/AlO x /Co 75 Fe 25 . 11 In this article we study magnetic anisotropies and magnetization reversal properties of epitaxial CCFA films deposited on Fe and Cr buffer layers.…”