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.

Antiferromagnetic Ordering and Uncoupled Spins in CaFe2O4 Thin Films Probed by Spin Hall Magnetoresistance

“…This negative SMR has been observed in easy-plane antiferromagnets such as NiO [26,27] and α − Fe 2 O 3 [28] and also in ferrimagnets close to the compensation temperature, where the spin-flop transition is possible at lower magnetic fields. [29][30][31][32] In addition, in an antiferromagnet, a tilt of the spins constituting the two magnetic sublattices in the direction of the field can also occur, inducing a net magnetization that affects the SMR response. [3] If the magnitude of such tilt is larger than 45° from the spin-flop direction, then this contribution will dominate and will give rise to an overall positive amplitude of the SMR.…”

“…This negative SMR has been observed in easy‐plane antiferromagnets such as NiO [ 26,27 ] and α − Fe 2 O 3 [ 28 ] and also in ferrimagnets close to the compensation temperature, where the spin‐flop transition is possible at lower magnetic fields. [ 29–32 ]…”