Solid-state synthesis, magnetic and structural properties of interfacial B2-FeRh(001) layers in Rh/Fe(001) films

V G Myagkov,M N Volochaev,G N Bondarenko,A A Ivanenko,L E Bykova,A A Matsynin,V S Zhigalov,D A Velikanov

doi:10.1038/s41598-020-67837-2

Abstract

Here we first report results of the start of the solid-state reaction at the Rh/Fe(001) interface and the structural and magnetic phase transformations in 52Rh/48Fe(001), 45Rh/55Fe(001), 68Rh/32Fe(001) bilayers from room temperature to 800 °C. For all bilayers the non-magnetic nanocrystalline phase with a B2 structure (nfm-B2) is the first phase that is formed on the Rh/Fe(001) interface near 100 °C. Above 300 °C, without changing the nanocrystalline B2 structure, the phase grows into the low-magnetization modification αlʹ (MSl ~ 825 emu/cm3) of the ferromagnetic αʹ phase which has a reversible αlʹ ↔ αʺ transition. After annealing 52Rh/48Fe(001) bilayers above 600 °C the αlʹ phase increases in grain size and either develops into αhʹ with high magnetization (MSh ~ 1,220 emu/cm3) or remains in the αlʹ phase. In contrast to αlʹ, the αhʹ ↔ αʺ transition in the αhʹ films is completely suppressed. When the annealing temperature of the 45Rh/55Fe(001) samples is increased from 450 to 800 °C the low-magnetization nanocrystalline αlʹ films develop into high crystalline perfection epitaxial αhʹ(001) layers, which have a high magnetization of ~ 1,275 emu/cm3. αhʹ(001) films do not undergo a transition to an antiferromagnetic αʺ phase. In 68Rh/32Fe(001) samples above 500 °C non-magnetic epitaxial γ(001) layers grow on the Fe(001) interface as a result of the solid-state reaction between the epitaxial αlʹ(001) and polycrystalline Rh films. Our results demonstrate not only the complex nature of chemical interactions at the low-temperature synthesis of the nfm-B2 and αlʹ phases in Rh/Fe(001) bilayers, but also establish their continuous link with chemical mechanisms underlying reversible αlʹ ↔ αʺ transitions.

Highlights

We first report results of the start of the solid-state reaction at the Rh/Fe(001) interface and the structural and magnetic phase transformations in 52Rh/48Fe(001), 45Rh/55Fe(001), 68Rh/32Fe(001) bilayers from room temperature to 800 °C
52Rh/48Fe(001) bilayers on a MgO(001) substrate during annealing from room temperature to 800 °C which builds on the X-ray diffraction (XRD) analysis (Fig. 1b) and magnetic measurements (Fig. 1c,d)
The transformations consist of the formation of a nonferromagnetic B2-FeRh phase thin layer at the Rh/Fe interface of the as-deposited sample, which above 300 °C turns into the αlphase

Summary

Introduction

We first report results of the start of the solid-state reaction at the Rh/Fe(001) interface and the structural and magnetic phase transformations in 52Rh/48Fe(001), 45Rh/55Fe(001), 68Rh/32Fe(001) bilayers from room temperature to 800 °C. An intriguing feature of the equilibrium diagram of the Fe-Rh system is the existence of the low-temperature transition at TKα→α ~ 100 °C between antiferromagnetic (AFM) αand ferromagnetic (FM) αphases in a narrow (0.48 < xRh < 056) concentration interval in chemically ordered B2-FeRh alloys[1]. This transition is accompanied by an isotropic volume expansion of ~ 1% of the B2-FeRh unit cell, which radically changes the magnetic properties, and changes the e ntropy[2,3] and r esistivity[4]. The main purpose of this article is to show the complex and intricate nature of the B2-FeRh phases synthesis, which begins to form on the Rh/Fe interface at ~ 100 °C

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Conclusion