Effects of Perpendicular Magnetic Field Annealing on the Structural and Magnetic Properties of [Co/Ni]2/PtMn Thin Films

Roshni Yadav,Chun-Hsien Wu,I-Fen Huang,Ko-Wei Lin,Xu Li,Te-Ho Wu

doi:10.3390/magnetochemistry7030038

Abstract

In this study, [Co/Ni]2/PtMn thin films with different PtMn thicknesses (2.7 to 32.4 nm) were prepared on Si/SiO2 substrates. The post-deposition perpendicular magnetic field annealing (MFA) processes were carried out to modify the structures and magnetic properties. The MFA process also induced strong interlayer diffusion, rendering a less sharp interface between Co and Ni and PtMn layers. The transmission electron microscopy (TEM) lattice image analysis has shown that the films consisted of face-centered tetragonal (fct) PtMn (ordered by MFA), body-centered cubic (bcc) NiMn (due to intermixing), in addition to face-centered cubic (fcc) Co, Ni, and PtMn phases. The peak shift (2-theta from 39.9° to 40.3°) in X-ray diffraction spectra also confirmed the structural transition from fcc PtMn to fct PtMn after MFA, in agreement with those obtained by lattice images in TEM. The interdiffusion induced by MFA was also evidenced by the depth profile of X-ray photoelectron spectroscopy (XPS). Further, the magnetic properties measured by vibrating sample magnetometry (VSM) have shown an increased coercivity in MFA-treated samples. This is attributed to the presence of ordered fct PtMn, and NiMn phases exchange coupled to the ferromagnetic [Co/Ni]2 layers. The vertical shift (Mshift = −0.03 memu) of the hysteresis loops is ascribed to the pinned spins resulting from perpendicular MFA processes.

Highlights

The discovery of magnetization switching by spin-orbit torques (SOT) has created new opportunities for digital and analog spintronic applications
Fukami et al showed the magnetization switching in the absence of applied field in the PtMn (AFM) and coupling field at the AFM/FM interface [12]. (Co/Ni) (FM) bilayer system with a perpendicular easy axis due to the exchange bias of the AFM [4]
We have studied the microstructure and magnetic properties of as-deposited and magnetic field annealed (MFA) Ag(8 nm)/[Co(2.5 nm)/Ni(2.3 nm)]2/PtMn(tPtMn) thin films

Summary

Introduction

The discovery of magnetization switching by spin-orbit torques (SOT) has created new opportunities for digital and analog spintronic applications. Fukami et al showed the magnetization switching in the absence of applied field in the PtMn (AFM) and Co/Ni (FM) bilayer system with a perpendicular easy axis due to the exchange bias of the AFM [4]. The transition from fcc to chemically ordered fct phase after the annealing facilities strong exchange coupling field at the AFM/FM interface [12]. Vergès et al studied the spin-orbit torque (SOT) switching in as-deposited and annealed Pt/[Co/Ni]2 /PtMn samples. The as-deposited sample shows no exchange bias effect, and the SOT switching is observed under in-plane applied field. We have studied the microstructure and magnetic properties of as-deposited and magnetic field annealed (MFA) Ag(8 nm)/[Co(2.5 nm)/Ni(2.3 nm)]2/PtMn(tPtMn) thin films. The correlation between the enhanced exchange coupling and the phase transition after magnetic field annealing provides a new understanding of the magnetism for multilayer

Results and Discussion

Materials and Methods

Conclusions