Field-induced Néel vector bi-reorientation of a ferrimagnetic insulator in the vicinity of compensation temperature*

Abstract

The spin Hall magnetoresistance (SMR) effect in Pt/Gd3Fe5O12 (GdIG) bilayers was systematically investigated. The sign of SMR changes twice with increasing magnetic field in the vicinity of the magnetization compensation point (T M) of GdIG. However, conventional SMR theory predicts the invariant SMR sign in the heterostructure composed of a heavy metal film in contact with a ferromagnetic or antiferromagnetic film. We conclude that this is because of the significant enhancement of the magnetic moment of the Gd sub-lattice and the unchanged moment of the Fe sub-lattice with a relatively large field, meaning that a small net magnetic moment is induced at T M. As a result, the Néel vector aligns with the field after the spin-flop transition, meaning that a bi-reorientation of the Néel vector is produced. Theoretical calculations based on the Néel’s theory and SMR theory also support our conclusions. Our findings indicate that the Néel-vector direction of a ferrimagnet can be tuned across a wide range by a relatively low external field around T M.