Suppression of spin rectification effects in spin pumping experiments

Spin pumping (SP) is a well-established method to generate pure spin currents allowing efficient spin injection into metals and semiconductors avoiding the problem of impedance mismatch. However, to disentangle pure spin currents from parasitic effects due to spin rectification effects (SRE) is a difficult task that is seriously hampering further developments. Here we propose a simple method that allows suppressing SRE contribution to inverse spin Hall effect (ISHE) voltage signal avoiding long and tedious angle-dependent measurements. We show an experimental study in the well-known Py/Pt system by using a coplanar waveguide (CPW). Results obtained demonstrate that the sign and size of the measured transverse voltage signal depends on the width of the sample along the CPW active line. A progressive reduction of this width evidences that SRE contribution to the measured transverse voltage signal becomes negligibly small for sample width below 200 μm. A numerical solution of the Maxwell equations in the CPW-sample setup, by using the Landau-Lifshitz equation with the Gilbert damping term (LLG) as the constitutive equation of the media, and with the proper set of boundary conditions, confirms the obtained experimental results.

Study on spin current transmission of Co1-x Tb x films

We investigate the spin to charge conversion phenomena in Y3Fe5O12/Pt/Co1-x Tb x /Pt multilayers by both the spin pumping and spin Seebeck effects. We find that the spin transport efficiency is irrelevant to magnetization states of the perpendicular magnetized Co1-x Tb x films, which can be attributed to the symmetry requirement of the inverse transverse spin Hall effect. Furthermore, the spin transmission efficiency is significantly affected by the film concentration, revealing the dominant role of extrinsic impurity scattering caused by Tb impurity. The present results provide further guidance for enhancing the spin transport efficiency and developing spintronics devices.

Ferromagnetic Resonance of a [GeTe/Sb2Te3]6/Py Superlattice

A [GeTe/Sb2Te3] superlattice is known as a topological insulator. It shows magnetic responses such as magneto-optical effect, magneto resistance, magneto capacitance, and so on. We have reported that [GeTe/Sb2Te3] superlattice film has a large spin–orbit interaction using a spin pumping method of a [GeTe/Sb2Te3]/Py superlattice. In this paper, we demonstrate a ST-FMR (spin transfer torque ferromagnetic resonance) of the [GeTe/Sb2Te3]6/Py superlattice, compared with a W/Py bilayer. The superlattice film showed a large resonance signal with a symmetric component. The ratio of symmetric components (S) to anti-symmetric (A) components (S/A) was 1.4, which suggests that the superlattice exhibits a large spin Hall angle. The [GeTe/Sb2Te3] superlattice will be suitable as a hetero-interface material required for high performance spintronics devices in future.

Resonant Precession of Magnetization and Precession - Induced DC voltages in FeGaB Thin Films

Measurements of frequency dependent ferromagnetic resonance (FMR) and spin pumping driven dc voltage (Vdc) are reported for amorphous films of Fe78Ga13B9 (FeGaB) alloy to address the phenomenon of self-induced inverse spin Hall effect (ISHE) in plain films of metallic ferromagnets. The Vdc signal, which is antisymmetric on field reversal, comprises of symmetric and asymmetric Lorentzians centered around the resonance field. Dominant role of thin film size effects is seen in setting the magnitude of static magnetization, Vdc and dynamics of magnetization precession in thinner films (≤ 8 nm). The film thickness dependence of magnetization parameters indicates the presence of a magnetically disordered region at the film – substrate interface, which may promote preferential flow of spins generated by the precessing magnetization towards the substrate. However, the Vdc signal also draws contributions from rectification effects of a ≈ 0.4 % anisotropic magnetoresistance and a large (≈ 54 nΩ.m) anomalous Hall resistivity (AHR) of these films which ride over the effect of spin – orbit coupling driven spin-to-charge conversion near the film – substrate interface. We have addressed these data in the framework of the existing theories of electrodynamics of a ferromagnetic film subjected to radio-frequency field in a coplanar waveguide geometry. Our estimation of the self-induced ISHE for the sample with 54 nΩ.m AHR shows that it may contribute significantly (≈ 90%) to the measured symmetric voltage. This study is expected to be very useful for fully understanding the spin pumping induced dc voltages in metallic ferromagnets with disordered interfaces and large anomalous Hall effect.