Paramagnetic spin Hall magnetoresistance

Abstract

Spin Hall magnetoresistance (SMR) refers to a resistance change in a metallic film reflecting the magnetization direction of a magnet attached to the film. The mechanism of this phenomenon is spin exchange between conduction-electron spins and magnetization at the interface. SMR has been used to read out information written in a small magnet and to detect magnetization dynamics, but it has been limited to magnets; magnetic ordered phases or instability of magnetic phase transition has been believed to be indispensable. Here, we report the observation of SMR in a paramagnetic insulator Gd 3 Ga 5 O 12 (GGG) without spontaneous magnetization combined with a Pt film. The paramagnetic SMR can be attributed to spin-transfer torque acting on localized spins in GGG. We determine the efficiencies of spin torque and spin-flip scattering at the Pt/GGG interface, and demonstrate these quantities can be tuned with external magnetic fields. The results clarify the mechanism of spin-transport at a metal/paramagnetic insulator interface, which gives new insight into the spintronic manipulation of spin states in paramagnetic systems.Spintronics 1 aims to add new functionalities to the conventional electronics using interconversion of spin angular momentum between different carriers in solids 2 . Especially, the spin exchange between conduction-electron spins in a normal metal (NM) and magnetization, M, in a ferromagnet (FM) is a central topic 3 to the branch of spintronics trying to manipulate M for developing new types of magnetic memory devices 4 . When spin angular momentum is transferred into a FM through a NM/FM interface (Fig. 1a), it modifies the transverse dynamics of M by exerting two types of torque, known as spin-transfer torque 5,6 (or damping-like torque) and field-like torque 7 , while it hardly couples to the longitudinal component. This is because the magnetic susceptibility in spin order, such as FM, is

Long distance magnon transport in the van der Waals antiferromagnet CrPS$_4$

“…At fields of several tesla, the SMR decreases with temperature but persists above T N and even up to room temperature (not shown), which is consistent with reports for CrPS 4 [17] and the van der Waals material Cr 2 Ge 2 Te 6 [22]. The robust SMR can possibly be ascribed to a T N that is enhanced by the interface spin orbit coupling and/or a paramagnetic SMR by a fieldinduced magnetization [23].…”

Strong Interfacial Exchange Field in a Heavy Metal/Ferromagnetic Insulator System Determined by Spin Hall Magnetoresistance

“…Spin transport in systems consisting of magnetic insulators (MIs) and nonmagnetic metals is of extreme importance in the field of spintronics. The spin currents through the interface of such a heterostructure are at the origin of many phenomena from spin pumping to spin Seebeck effect or spin Hall magnetoresistance. − The spin transport at the interface can be described in terms of three parameters: the spin-sink conductance G s , which originates when the electron spins of the nonmagnetic metal are collinear with the MI magnetization, − and the real and imaginary parts of the spin-mixing conductance, G ↑↓ = G r + iG i (refs and ), which originate from torques that the electron spins of the nonmagnetic metal exert to the magnetization of the MI when they are noncollinear. G r is determined by the Slonczewski (or damping-like) torque, an important quantity for current-induced magnetization switching in spin-transfer torque magnetic random-access memory (STT-MRAM) devices, currently ready for mass production, as well as in spin–orbit torque devices. , On the other hand, G i quantifies the exchange field between the electrons of the nonmagnetic metal and the magnetic moments of the MI, exerting a field-like torque when spin accumulation is induced.…”

“…When a heavy metal (HM) with a sizable spin Hall effect is placed in contact with a MI, the SMR appears as a modulation of the HM resistivity, governed by G r – G s (ref ), which follows the relative orientation between the magnetization ( M ) in the MI and the spin-Hall induced spin accumulation ( μ s ) in the HM. SMR has been extensively studied in different MIs, for instance, ferrimagnetic insulators such as Y 3 Fe 5 O 12 (refs − ), Tm 3 Fe 5 O 12 (refs and ), Gd 3 Fe 5 O 12 (compensated ferrimagnet) or Cu 2 OSeO 3 (spiral ferrimagnet), antiferromagnetic insulators such as NiO, Cr 2 O 3 , and CoO (refs − ), low-dimensional ferromagnets, or even paramagnetic insulators. − SMR also shows up as an anomalous Hall-like contribution in the HM in this case governed by G i (refs , , and ). In the studied cases with ferrimagnetic garnets, G r is at least 1 order of magnitude larger than G i (refs − , , , ).…”

Mechanism of paramagnetic spin Seebeck effect

“…It is worth mentioning that Eq. (11) gives the general form of the interfacial spin current at NM/PI, which can be applied to the SSEs as well as the nonlocal spin transport [45] and spin Hall magnetoresistance [38,46] with paramagnetic insulators.…”