Identification of Néel vector orientation in antiferromagnetic domains switched by currents in NiO/Pt thin films

Abstract

Efficient electrical read-out and writing of antiferromagnetic (AFM) insulators is a key prerequisite in view of using this class of materials as active elements in spintronic applications. The understanding of the electrical manipulation of the antiferromagnetic order n is a crucial aspect to exploit the advantages these materials exhibit compared to ferromagnets, such as THz dynamics, enhanced stability with respect to interfering magnetic fields and higher bit packing densities due to the absence of stray fields [1]. The absence of a net magnetic moment in antiferromagnets makes manipulation using conventional magnetic fields challenging. Recently, several reports demonstrated current-induced writing of the Néel order orientation in antiferromagnets and different switching mechanisms have been put forward [2-5]. The mechanisms depend on the type of domains present in AFM thin films. So far, however, it is largely unknown between which types of domains electrical switching occurs and in which direction the Néel vector is pointing. There are reports stating that in MgO//NiO the tensile strain induces a preferential out-of-plane orientation of n with respect to the sample plane [2] and on the other hand the Néel vector switching is detected electrically by spin Hall magnetoresistance (SMR) measurements, sensitive to the in-plane components of n, thus indicating the presence of an in-plane component of the Néel vector [6]. In our work [7] we focus on collinear insulating antiferromagnetic NiO/Pt thin films as a materials platform, and we image reversible electrical switching by photoemission electron microscopy (PEEM) employing the x-ray magnetic linear dichroism (XMLD) effect (Fig.1). By varying the x-ray polarization, energy and sample azimuthal angle, we identify the crystallographic orientation of the domains that can be switched by currents and quantify the Néel vector direction changes, showing that the switching occurs between different T-domains. The Néel vector orientation in these domains shows an enlarged out-of-plane component pointing along [±1 ±1 3.8], different from the bulk <112> directions. The final state of the in-plane component of the Néel vector n after switching in a Hall cross geometry by current pulses j along the [1 ±1 0] directions is n||j in the centre of the device. **