The irreversible thermodynamics of a continuous medium with magnetic dipoles predicts that a temperature gradient in the presence of magnetization waves induces a magnetic induction field, which is the magnetic analog of the Seebeck effect. This thermal gradient modulates the precession and relaxation. The magnetic Seebeck effect implies that magnetization waves propagating in the direction of the temperature gradient and the external magnetic induction field are less attenuated, while magnetization waves propagating in the opposite direction are more attenuated.
The damping of spin waves transmitted through a two-port magnonic device implemented on a yttrium iron garnet thin film is shown to be proportional to the temperature gradient imposed on the device. The sign of the damping depends on the relative orientation of the magnetic field, the wave vector, and the temperature gradient. The observations are accounted for qualitatively and quantitatively by using an extension of the variational principle that leads to the Landau-Lifshitz equation. All parameters of the model can be obtained by independent measurements. DOI: 10.1103/PhysRevB.95.104432 The discovery of giant magnetoresistance (GMR) revolutionized information storage technology [1,2] and the spin-transfer torque (STT), predicted two decades ago by Slonczewski [3] and Berger [4], may reshape once again the magnetic memory industry [5]. The concept of a heat-driven spin torque, or thermal spin-transfer torque (TST), has been suggested [6][7][8] and opened the world of spin caloritronics. Magnetic insulators are ideal for studying the fundamentals of spin caloritronics, because they are free of the effect of heat on charge transport. Here, we demonstrate that a spin torque can be induced in magnetic insulators by applying a thermal gradient. The effect is not linked to spin-dependent transport at interfaces since we observe a heat-driven contribution to damping of magnetization waves on a millimeter scale. We show that by adding to M(r) the bound magnetic current (∇ × M) as state variable, the variational principle that yields the Landau-Lifshitz equation predicts the presence of a thermal spin torque, from which we derive an expression for spin currents in insulators. Our experiments verify the key predictions of this model. Thermodynamics can predict a link between heat and magnetization, but cannot determine the strength of the effect [9].Spin caloritronics studies the interplay of spin, charge, and heat transport [10]. As the spin dependence of the electrical conductivity proved to be important since it gives rise to GMR, the spin dependence of other transport parameters has been investigated, such as that of the Seebeck [11] and Peltier coefficients [12]. The combination of heat with spin and charge transport gained widespread attention owing to studies of the spin Seebeck effect [13,14]. The STT effect which uses a spinpolarized electrical current has shown promising applications, e.g., in magnetic memories (STT-MRAM). It was already established that heat flowing through a ferromagnetic metal can generate a diffusive spin current [15] which induces a spin torque when flowing through a magnetic nanostructure [6]. Experimentally, this effect was studied in Co/Cu/Co spin valve nanowires by observing the change in the switching * haiming.yu@buaa.edu.cn † jean-philippe.ansermet@epfl.ch field of magnetization due to a local thermal gradient [7]. It was later shown that heat couples to magnetization dynamics [16][17][18]. The effect of heat on magnetization was also found in magnetic tunnel junctions [19] and...
The existence of a heat-driven spin torque is demonstrated using Co/Cu/Co spin valves embedded in metallic nanowires. Heat currents flowing in one direction or its opposite were obtained by heating optically one end or the other of the nanowires. The spin torque associated with the heat-driven spin current pushes the magnetization out of equilibrium, resulting in a change of the magnetoresistance, which is detected using a charge current small enough not to cause heating or induced fields of any significance. The giant magnetoresistance response to this torque peaks with the magnetic susceptibility, whereas the spurious signal coming from the temperature dependence of the resistance produces merely a field independent baseline.
An analytical model of the spin-diode effect induced by resonant spin-transfer torque in a ferromagnetic bilayer with strong dipolar coupling provides the resonance frequencies and the lineshapes of the magnetic field spectra obtained under field or laser-light modulation. The effect of laser irradiation is accounted for by introducing the temperature dependence of the saturation magnetization and anisotropy, as well as thermal spin-transfer torques. The predictions of the model are compared with experimental data obtained with single Co/Cu/Co spin valves, embedded in nanowires and produced by electrodeposition. Temperature modulation provides excellent signal-to-noise ratio. High temperature-modulation frequency is possible because these nanostructures have a very small heat capacity and are only weakly heat-sunk. The two forms of modulation give rise to qualitative differences in the spectra that are accounted for by the model. 76.50.+g, 75.47.De
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.