arXiv subjects

Sibylle Meyer

Publications and source records attributed to Sibylle Meyer.

12 recordsLinked to original sources

arXiv2020

Static magnetic proximity effects and spin Hall magnetoresistance in Pt/Y$_{3}$Fe$_{5}$O$_{12}$ and inverted Y$_{3}$Fe$_{5}$O$_{12}$/Pt bilayers

The magnetic state of heavy metal Pt thin films in proximity to the ferrimagnetic insulator Y$_{3}$Fe$_{5}$O$_{12}$ has been investigated systematically by means of x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity measurements combined with angle-dependent magnetotransport studies. To reveal intermixing effects as the possible cause for induced magnetic moments in Pt, we compare thin film heterostructures with different order of the layer stacking and different interface properties. For standard Pt layers on Y$_{3}$Fe$_{5}$O$_{12}$ thin films, we do not detect any static magnetic polarization in Pt. These samples show an angle-dependent magnetoresistance behavior, which is consistent with the established spin Hall magnetoresistance. In contrast, for the inverted layer sequence, Y$_{3}$Fe$_{5}$O$_{12}$ thin films grown on Pt layers, Pt displays a finite induced magnetic moment comparable to that of all-metallic Pt/Fe bilayers. This magnetic moment is found to originate from finite intermixing at the Y$_{3}$Fe$_{5}$O$_{12}$/Pt interface. As a consequence, we found a complex angle-dependent magnetoresistance indicating a superposition of the spin Hall and the anisotropic magnetoresistance in these type of samples. Both effects can be disentangled from each other due to their different angle dependence and their characteristic temperature evolution.

cond-mat.mtrl-sci↗

arXiv2017

Observation of the spin Nernst effect

The observation of the spin Hall effect triggered intense research on pure spin current transport. With the spin Hall effect, the spin Seebeck effect, and the spin Peltier effect already observed, our picture of pure spin current transport is almost complete. The only missing piece is the spin Nernst (-Ettingshausen) effect, that so far has only been discussed on theoretical grounds. Here, we report the observation of the spin Nernst effect. By applying a longitudinal temperature gradient, we generate a pure transverse spin current in a Pt thin film. For readout, we exploit the magnetization-orientation-dependent spin transfer to an adjacent Yttrium Iron Garnet layer, converting the spin Nernst current in Pt into a controlled change of the longitudinal thermopower voltage. Our experiments show that the spin Nernst and the spin Hall effect in Pt are of comparable magnitude, but differ in sign, as corroborated by first-principles calculations.

cond-mat.mes-hall↗

arXiv2016

Detection of DC currents and resistance measurements in longitudinal spin Seebeck effect experiments on Pt/YIG and Pt/NFO

In this work we investigated thin films of the ferrimagnetic insulators YIG and NFO capped with thin Pt layers in terms of the longitudinal spin Seebeck effect (LSSE). The electric response detected in the Pt layer under an out-of-plane temperature gradient can be interpreted as a pure spin current converted into a charge current via the inverse spin Hall effect. Typically, the transverse voltage is the quantity investigated in LSSE measurements (in the range of μV). Here, we present the directly detected DC current (in the range of nA) as an alternative quantity. Furthermore, we investigate the resistance of the Pt layer in the LSSE configuration. We found an influence of the test current on the resistance. The typical shape of the LSSE curve varies for increasing test currents.

cond-mat.mtrl-sci↗

arXiv2015

Anomalous Hall effect in YIG$|$Pt bilayers

We measure the ordinary and the anomalous Hall effect in a set of yttrium iron garnet$|$platinum (YIG$|$Pt) bilayers via magnetization orientation dependent magnetoresistance experiments. Our data show that the presence of the ferrimagnetic insulator YIG leads to an anomalous Hall like signature in Pt, sensitive to both Pt thickness and temperature. Interpretation of the experimental findings in terms of the spin Hall anomalous Hall effect indicates that the imaginary part of the spin mixing interface conductance $G_{\mathrm{i}}$ plays a crucial role in YIG$|$Pt bilayers. In particular, our data suggest a sign change in $G_{\mathrm{i}}$ between $10\,\mathrm{K}$ and $300\,\mathrm{K}$. Additionally, we report a higher order Hall effect, which appears in thin Pt films on YIG at low temperatures.

cond-mat.mtrl-sci↗

arXiv2014

Spin Hall noise

We measure the low-frequency thermal fluctuations of pure spin current in a Platinum film deposited on yttrium iron garnet via the inverse spin Hall effect (ISHE)-mediated voltage noise as a function of the angle $α$ between the magnetization and the transport direction. The results are consistent with the fluctuation dissipation theorem in terms of the recently discovered spin Hall magnetoresistance (SMR). We present a microscopic description of the $α$ dependence of the voltage noise in terms of spin current fluctuations and ISHE.

cond-mat.mes-hall↗

arXiv2014

Time resolved spin Seebeck effect experiments

In this Letter, we present the results of transient thermopower experiments, performed at room temperature on yttrium iron garnet/platinum bilayers. Upon application of a time-varying thermal gradient, we observe a characteristic low-pass frequency response of the ensuing thermopower voltage with cutoff frequencies of up to 37 MHz. We interpret our results in terms of the spin Seebeck effect, and argue that small wavevector magnons are of minor importance for the spin Seebeck effect in our thin film hybrid structures.

cond-mat.mes-hall↗

arXiv2014

Temperature dependent spin transport properties of Platinum inferred from spin Hall magnetoresistance measurements

We study the temperature dependence of the spin Hall magnetoresistance (SMR) in yttrium iron garnet/platinum hybrid structures via magnetization orientation dependent magnetoresistance measurements. Our experiments show a decrease of the SMR magnitude with decreasing temperature. Using the sensitivity of the SMR to the spin transport properties of the normal metal, we interpret our data in terms of a decrease of the spin Hall angle in platinum from 0.11 at room temperature to 0.075 at 10K, while the spin diffusion length and the spin mixing conductance of the ferrimagnetic insulator/normal metal interface remain almost constant.

cond-mat.mes-hall↗

arXiv2014

Origin of the spin Seebeck effect probed by temperature dependent measurements in Gd$_{3}$Fe$_{5}$O$_{12}$

We probe the spin Seebeck effect in Gd$_{3}$Fe$_{5}$O$_{12}$/Pt hybrid structures as a function of temperature and observe two sign changes of the spin Seebeck signal with decreasing temperature. A first sign change occurs at a temperature close to the Gd$_{3}$Fe$_{5}$O$_{12}$ magnetic compensation point at around 280 K. There the spin Seebeck signal changes sign abruptly with unaltered amplitude, indicating that the spin current is mainly caused by the magnetic Fe sub-lattices, which reorient their directions at this temperature. A second, more gradual sign change takes place around the ordering temperature of the Gd sub-lattice in the range of 65-85 K, showing that the Gd magnetic sub-lattice dominates the thermally driven spin current at lower temperatures. These sign changes together with the non-monotonous dependence of the spin Seebeck signal on the temperature demonstrate that the magnonic spin current is not simply replicating the effective magnetization of Gd$_{3}$Fe$_{5}$O$_{12}$. Rather, the thermally generated net spin current results from a complex interplay of the three magnetic sub-lattices involved.

cond-mat.mes-hall↗

arXiv2013

Current heating induced spin Seebeck effect

A new measurement technique for the spin Seebeck effect is presented, wherein the normal metal layer used for its detection is exploited simultaneously as a resistive heater and thermometer. We show how the various contributions to the measured total signal can be disentangled, allowing to extract the voltage signal solely caused by the spin Seebeck effect. To this end we performed measurements as a function of the external magnetic field strength and its orientation. We find that the effect scales linearly with the induced rise in temperature, as expected for the spin Seebeck effect.

cond-mat.mes-hall↗

arXiv2013

Experimental test of the spin mixing interface conductivity concept

We perform a quantitative, comparative study of the spin pumping, spin Seebeck and spin Hall magnetoresistance effects, all detected via the inverse spin Hall effect in a series of over 20 yttrium iron garnet/Pt samples. Our experimental results fully support present, exclusively spin current-based, theoretical models using a single set of plausible parameters for spin mixing conductance, spin Hall angle and spin diffusion length. Our findings establish the purely spintronic nature of the aforementioned effects and provide a quantitative description in particular of the spin Seebeck effect.

cond-mat.mtrl-sci↗

arXiv2013

Quantitative study of the spin Hall magnetoresistance in ferromagnetic insulator/normal metal hybrids

We experimentally investigate and quantitatively analyze the spin Hall magnetoresistance effect in ferromagnetic insulator/platinum and ferromagnetic insulator/nonferromagnetic metal/platinum hybrid structures. For the ferromagnetic insulator we use either yttrium iron garnet, nickel ferrite or magnetite and for the nonferromagnet copper or gold. The spin Hall magnetoresistance effect is theoretically ascribed to the combined action of spin Hall and inverse spin Hall effect in the platinum metal top layer. It therefore should characteristically depend upon the orientation of the magnetization in the adjacent ferromagnet, and prevail even if an additional, nonferromagnetic metal layer is inserted between Pt and the ferromagnet. Our experimental data corroborate these theoretical conjectures. Using the spin Hall magnetoresistance theory to analyze our data, we extract the spin Hall angle and the spin diffusion length in platinum. For a spin mixing conductance of $4\times10^{14}\;\mathrm{Ω^{-1}m^{-2}}$ we obtain a spin Hall angle of $0.11\pm0.08$ and a spin diffusion length of $(1.5\pm0.5)\;\mathrm{nm}$ for Pt in our thin film samples.

cond-mat.mes-hall↗

arXiv2012

Investigation of induced Pt magnetic polarization in Pt/Y3Fe5O12 bilayers

Using X-ray magnetic circular dichroism (XMCD) measurements, we explore the possible existence of induced magnetic moments in thin Pt films deposited onto the ferrimagnetic insulator yttrium iron garnet (Y3Fe5O12). Such a magnetic proximity effect is well established for Pt/ferromagnetic metal heterostructures. Indeed, we observe a clear XMCD signal at the Pt L3 edge in Pt/Fe bilayers, while no such signal can be discerned in XMCD traces of Pt/Y3Fe5O12 bilayers. Integrating the XMCD signals allows to estimate an upper limit for the induced Pt magnetic polarization in Pt/Y3Fe5O12 bilayers.

cond-mat.mtrl-sci↗