Oscillatory magnetic coupling in amorphous CoSiB/Pt/CoSiB structure

Abstract

Ferromagnetic materials with perpendicular magnetic anisotropy (PMA) have great attention due to the high thermal stability and low switching current density for next generation memory devices such as spin-transfer-torque magnetic random access memory (STT-MRAM). The amorphous CoSiB/Pt multilayers are one of PMA candidates as STT-MRAM free layers and domain wall (DW) logic devices.[1] In this paper, we focus on the magnetic interaction between two CoSiB layers separated by a Pt layer. We have grown the CoSiB(15 A)/Pt(t)/CoSiB(15 A) sandwich structures with different Pt thickness t ranging from 14 to 30 A by using DC sputtering method, and measured the anomalous Hall effect (AHE) at room temperature. The magnitudes of Hall voltage signals are oscillating as a function of the Pt thickness, resembling the oscillatory behavior observed for the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction. For t = 22 and 27 A, clear signals from the antiferromagnetic coupling have been seen in both AHE and magnetization data. In order to exploit the mechanism of indirect interlayer coupling, we have also measured the AHE as a function of perpendicular field H z in an external magnetic field of H x or H y parallel to the film plane. Interestingly, all AHE data show a shift of hysteresis loop, similar to an exchange bias effect found in ferromagnetic/antiferromagnetic bilayer structure. We analyze these peculiar behavior based on the Stoner-Wohlfarth model.[2]