Co2Fe(Al1−xSix) heusler alloys and their applications to spintronics

Abstract

This work reports on the structural and magnetic properties of the Heusler Co2FeAlxSi1−x epitaxial thin films and their applications to magnetic tunnel junctions (MTJs), giant magnetoresistive (GMR) devices and spin transfer magnetization switching. It is shown for Co2FeAlxSi1−x that the Fermi level position can be tuned by the composition. The temperature dependence of the tunneling magneto resistance (TMR) in epitaxial MTJs using B2-Co2FeAl0.5Si0.5 (CFAS) electrode is fitted well by a spin wave excitation model for tunneling spin polarization. Half-metallic B2-CFAS provided a large GMR up to 34 % at room temperature. Magnetization switching was observed in the resistance-current curves and exhibited a two-step switching process originating from the interplay between the magnetocrystalline anisotropy of the CFAS layers and the spin-transfer torque. A small average intrinsic switching current density is obtained by analyzing the data using the thermal activation model. The results show that the use of the Heusler alloy CFAS with high spin polarization is an effective way to reduce the switching current density even in MTJs.