Antiferromagnetic Cr-Mn alloys: Crystal structure, magnetic anisotropy, and exchange bias in magnetron-sputtered polycrystalline thin films

Abstract

In this paper we study the formation of the antiferromagnetic Cr-Mn alloys with body-centered cubic crystal structure, and their capability to act as a pinning layer for the exchange bias effect in magnetron-sputtered polycrystalline films. By means of X-ray diffractometry, executed in different geometries, we perform a thorough analysis of Ta/Cr-Mn/Ta films, which results in the construction of a room-temperature phase diagram of Cr-Mn. These results combined with magnetic measurements of films with adjacent antiferromagnetic Cr-Mn and ferromagnetic Fe20Ni80 layers allow us to establish the conditions for the observation of the exchange bias effect, the maximum blocking temperature Tb of which can be as high as 540 K. Employing a specialized measurement protocol, we estimate the effective anisotropy constant Keff, whose values help to explain thickness dependence of the exchange bias field in structures with a Cr-Mn pinning layer.