Giant spin Nernst effect induced by resonant scattering at surfaces of metallic films

Abstract

A new concept realizing giant spin Nernst effect in nonmagnetic metallic films is introduced. It is based on the idea of engineering an asymmetric energy dependence of the longitudinal and transverse electrical conductivities, as well as a pronounced energy dependence of the spin Hall angle in the vicinity of the Fermi level by the resonant impurity states at the Fermi level. We employ an analytical model and demonstrate the emergence of a giant spin Nernst effect in Ag(111) films using ab-inito calculations combined with the Boltzmann approach for transport properties arising from skew scattering off impurities. PACS numbers: 72.25.Rb, 73.50.Bk, 72.25.Ba, Within the past few years, the field of spin caloric transport has attracted broad interest owing to new challenges and vistas in applications which combine spintronic as well as thermoelectric concepts [1]. In this field, thermal gradient is used as an ultimate agent to generate a spin current, in analogy to the generation of a charge current in conventional thermoelectrics. As a promiment spincaloritronics phenomenon, the relativistic spin Nernst effect (SNE) enables a way to generate a pure transverse spin current in a sample subject to an applied temperature gradient [2][3][4]. The SNE bears an analogy to the spin Hall effect (SHE) [5,6], which has become one of the most efficient ways of generating spin currents in spintronics. Owing to the fact that the SHE has been successfully observed in various types of experiments [7][8][9], it is expected that the spin Nernst effect would also be detectable. However, limitations on the magnitude of temperature gradients in metals can diminish the magnitude of the spin Nernst currents [10].Ab-initio studies [11][12][13][14] and experiments [15] suggest that the extrinsic SHE induced by the skew-scattering off impurities can be large due to a large difference in the spin-orbit coupling strength of the impurities and the host. However, this argument is not applicable to the SNE, because the thermal transport coefficients entering the expression for the spin Nernst conductivity (SNC) are determined to a first approximation by the derivative of the conductivities around the Fermi energy (E F ), and not by the their values directly at it. As a consequence, the SNE is more sensitive to changes in the electronic structure as a function of energy, as compared to the SHE. A requirement for the SNC to be large is that the energy dependence of the conductivities should be very asymmetric with respect to E F .Recently, Tauber et al. [10,16], using first-principles techniques combined with Boltzmann approach, computed the SNE in Cu bulk, caused by spin-dependent scattering off substitutional impurities such as Ti, Au, Bi. The magnitude of the SNC was predicted to be about 16 (A/K m) at 300 K in Cu 0.99 Au 0.01 alloy. It corresponds to a spin current of about 10 µA when using a sample with the dimensions of 100×100×100 nm [9] and a temperature gradient of 50 K/µm [17]. For the same Cu(Au) alloy, Wimmer et al. obtained a somewhat ...

Anomalous Nernst effect in Ir22Mn78/Co20Fe60B20/MgO layers with perpendicular magnetic anisotropy

“…Therefore, a change in film resistivity may only play a slight role in AHE and ANE enhancement. Our results on N ANE and Hall resistivity are consistent with the idea that what the observed large Nernst effect is due to the interface between IrMn and CoFeB, e.g., a proximity effect 48,49 or an interfacial exchange interaction. [50][51][52] Moreover, the polarity of the AHE and ANE signal changed after the IrMn layer was inserted, as shown in Figs 39 It is not clear why there is such a large difference between our results and theirs.…”

Orbital Nernst Effect of Magnons

“…3 we summarize the non-trivial dependence of the ONE on temperature and on the model parameters, as well as its correlation with the topology of the magnon bands. Although the ONE has a distinct microscopic origin in the orbital electron-magnon coupling, our prediction is that the corresponding conductivity can reach the order of k B /π [51], which is comparable to the values known for the spin Nernst effect of magnons or spin Nernst effect of electrons [12,13,16,46,[52][53][54]. This underlines the strong potential of ONE for the realm of spincaloritronics.…”

Spin caloric transport from density-functional theory

“…by lowering of the temperature or concentration of impurities) the magnitude of the TSOT, qualitatively proportional to the degree of raggedness of the torkance as a function of energy, can be significantly enhanced. Since the SNE is directly proportional to the degree of the changes that the SHC experiences around the Fermi energy, a promising way of engineering the magnitude of the SNE is to exploit the drastic effect that the impurity scattering in the dilute limit can have on the energy-dependence of the spin Hall effect [84]. Overall, tuning the details of disorder by alloying, phonons, magnetic excitations, substitutional disorder etc can provide a fruitful path towards technologically relevant applications of the thermal spin-orbit torque.…”