Anomalous Nernst effect in thin films of non-collinear antiferromagnet Mn3NiN

Abstract

Antiferromagnetic materials with non-collinear spin structures (NC-AFMs) offer significant potential for spintronic applications[1]. They have vanishingly small magnetization and ultrafast spin dynamics. In addition, they allow for the presence of important counterparts to the effects considered to be exclusive to materials with net magnetization, such as the anomalous Hall effect (AHE)[2], magneto-optical Kerr effect[3] or anomalous Nernst effect (ANE)[4]. One of the promising candidates of the NC-AFM class are Mn antiperovskites, with a typical representative being Mn3NiN.In this contribution we present ANE measurements on epitaxial thin films of Mn3NiN prepared on SrTiO3 substrate with spin structure lying in the (111) plane. Previous theoretical predictions suggest that despite the modest spin-orbit coupling, the magnitude of the ANE in Mn3NiN ought to exceed that of Mn3Sn NC-AFM due to the Berry phase boost[5].We implement two complementary methods to detect the ANE response of the Mn3NiN films. First, the global Nernst response is measured using a micro-patterned Hall bar device with platinum resistive heaters generating an in-plane thermal gradient. The measured anomalous Nernst data (Fig.1(a)) are in good agreement with the AHE measurements[5], indicating a similar physical origin of the two effects. Second, to add a spatial resolution, scanning thermal gradient microscopy[4] is used. A laser beam incident on a micro-patterned device induces thermal gradients. The method reveals the sample’s domain structure. We find a signature of an ANE component that we can control with the external field due to the unsaturated moment present lying in the (111) plane, different from the previously measured Mn3Sn. This small moment provides a means for manipulating magnetic order, and even writing magnetic domain-like structures (Fig.1(b)). These two methods provide fruitful insight into the magnetic behaviour of NC-AFMs.  Fig.1. Anomalous Nernst effect in Mn3NiN. (a) Global ANE as a function of the out-of-plane magnetic field at different base temperatures. (b) Scanning thermal gradient microscopy at T = 100 K. The domain-like structure was written by high-intensity laser beam and 500 mT in-plane magnetic field.