Search results for "CORRELATED"
showing 10 items of 1174 documents
Spin-order dependent anomalous Hall effect and magneto-optical effect in noncollinear antiferromagnets Mn$_{3}X$N ($X$ = Ga, Zn, Ag, and Ni)
2019
Noncollinear antiferromagnets (AFMs) have recently attracted a lot of attention owing to the potential emergence of exotic spin orders on geometrically frustrated lattices, which can be characterized by corresponding spin chiralities. By performing first-principles density functional calculations together with group-theory analysis and tight-binding modelling, here we systematically study the spin-order dependent anomalous Hall effect (AHE) and magneto-optical effect (MOE) in representative noncollinear AFMs Mn$_{3}X$N ($X$ = Ga, Zn, Ag, and Ni). The symmetry-related tensor shape of the intrinsic anomalous Hall conductivity (IAHC) for different spin orders is determined by analyzing the rel…
Topological insulators and thermoelectric materials
2012
Topological insulators (TIs) are a new quantum state of matter which have gapless surface states inside the bulk energy gap. Starting with the discovery of two dimensional TIs, the HgTe-based quantum wells, many new topological materials have been theoretically predicted and experimentally observed. Currently known TI materials can possibly be classified into two families, the HgTe family and the Bi2Se family. The signatures found in the electronic structure of a TI also cause these materials to be excellent thermoelectric materials. On the other hand, excellent thermoelectric materials can be also topologically trivial. Here we present a short introduction to topological insulators and the…
Spin Hall effect
2014
Spin Hall effects are a collection of relativistic spin-orbit coupling phenomena in which electrical currents can generate transverse spin currents and vice versa. Although first observed only a decade ago, these effects are already ubiquitous within spintronics as standard spin-current generators and detectors. Here we review the experimental and theoretical results that have established this sub-field of spintronics. We focus on the results that have converged to give us a clear understanding of the phenomena and how they have evolved from a qualitative to a more quantitative measurement of spin-currents and their associated spin-accumulation. Within the experimental framework, we review …
Monitoring surface resonances on Co2MnSi(100) by spin-resolved photoelectron spectroscopy
2015
The magnitude of the spin polarization at the Fermi level of ferromagnetic materials at room temperature is a key property for spintronics. Investigating the Heusler compound Co$_2$MnSi a value of 93$\%$ for the spin polarization has been observed at room temperature, where the high spin polarization is related to a stable surface resonance in the majority band extending deep into the bulk. In particular, we identified in our spectroscopical analysis that this surface resonance is embedded in the bulk continuum with a strong coupling to the majority bulk states. The resonance behaves very bulk-like, as it extends over the first six atomic layers of the corresponding (001)-surface. Our study…
Spin transport in multilayer systems with fully epitaxial NiO thin films
2018
We report the generation and transport of thermal spin currents in fully epitaxial $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{F}{\mathrm{e}}_{2}{\mathrm{O}}_{3}/\mathrm{NiO}(001)/\mathrm{Pt}$ and $\mathrm{F}{\mathrm{e}}_{3}{\mathrm{O}}_{4}/\mathrm{NiO}(001)/\mathrm{Pt}$ trilayers. A thermal gradient, perpendicular to the plane of the sample, generates a magnonic spin current in the ferrimagnetic maghemite $(\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{F}{\mathrm{e}}_{2}{\mathrm{O}}_{3})$ and magnetite $(\mathrm{F}{\mathrm{e}}_{3}{\mathrm{O}}_{4})$ thin films by means of the spin Seebeck effect. The spin current propagates across the epitaxial, antiferromagnetic insulating NiO layer…
Revealing the importance of interfaces for pure spin current transport
2021
Spin transport phenomena underpin an extensive range of spintronic effects. In particular spin transport across interfaces occurs in most device concepts, but is so far poorly understood. As interface properties strongly impact spin transport, one needs to characterize and correlate them to the fabrication method. Here we investigate pure spin current transport across interfaces and connect this with imaging of the interfaces. We study the detection of pure spin currents via the inverse spin Hall effect in Pt and the related spin current absorption by Pt in Py-Cu-Pt lateral spin valves. Depending on the fabrication process, we either find a large (inverse) spin Hall effect signal and low sp…
Full angular dependence of the spin Hall and ordinary magnetoresistance in epitaxial antiferromagnetic NiO(001)/Pt thin films
2018
We report the observation of the three-dimensional angular dependence of the spin Hall magnetoresistance (SMR) in a bilayer of the epitaxial antiferromagnetic insulator NiO(001) and the heavy metal Pt, without any ferromagnetic element. The detected angular-dependent longitudinal and transverse magnetoresistances are measured by rotating the sample in magnetic fields up to 11 T, along three orthogonal planes (xy-, yz- and xz-rotation planes, where the z-axis is orthogonal to the sample plane). The total magnetoresistance has contributions arising from both the SMR and ordinary magnetoresistance. The onset of the SMR signal occurs between 1 and 3 T and no saturation is visible up to 11 T. Th…
Reconstruction of an effective magnon mean free path distribution from spin Seebeck measurements in thin films
2017
A thorough understanding of the mean-free-path (MFP) distribution of the energy carriers is crucial to engineer and tune the transport properties of materials. In this context, a significant body of work has investigated the phonon and electron MFP distribution, however, similar studies of the magnon MFP distribution have not been carried out so far. In this work, we used thickness-dependence measurements of the longitudinal spin Seebeck (LSSE) effect of yttrium iron garnet films to reconstruct the cumulative distribution of a SSE related effective magnon MFP. By using the experimental data reported by Guo et al. [Phys. Rev. X 6, 031012 (2016)], we adapted the phonon MFP reconstruction algo…
Interface enhancement of Gilbert damping from first-principles
2014
The enhancement of Gilbert damping observed for Ni_{80}Fe_{20} (Py) films in contact with the nonmagnetic metals Cu, Pd, Ta, and Pt is quantitatively reproduced using first-principles scattering calculations. The "spin-pumping" theory that qualitatively explains its dependence on the Py thickness is generalized to include a number of extra factors known to be important for spin transport through interfaces. Determining the parameters in this theory from first principles shows that interface spin flipping makes an essential contribution to the damping enhancement. Without it, a much shorter spin-flip diffusion length for Pt would be needed than the value we calculate independently.
Imaging of current induced Néel vector switching in antiferromagnetic Mn 2 Au
2019
The effects of current induced N\'eel spin-orbit torques on the antiferromagnetic domain structure of epitaxial Mn$_2$Au thin films were investigated by X-ray magnetic linear dichroism - photoemission electron microscopy (XMLD-PEEM). We observed current induced switching of AFM domains essentially corresponding to morphological features of the samples. Reversible as well as irreversible N\'eel vector reorientation was obtained in different parts of the samples and the switching of up to 30 % of all domains in the field of view of 10 $\mu$m is demonstrated. Our direct microscopical observations are compared to and fully consistent with anisotropic magnetoresistance effects previously attribu…