0000000000023211
AUTHOR
Er-jia Guo
Origin of the spin Seebeck effect in compensated ferrimagnets
Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist that can affect the dynamical response. Here we show that the spin Seebeck effect (SSE) is sensitive to the complexities of the magnon spectrum. The SSE is caused by thermally excited spin dynamics that are converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the SSE in the ferrimagnet gadolinium iron garne…
Influence of thickness and interface on the low-temperature enhancement of the spin Seebeck effect in YIG films
The temperature-dependent longitudinal spin Seebeck effect (LSSE) in heavy metal (HM)/Y_{3}Fe_{5}O_{12} (YIG) hybrid structures is investigated as a function of YIG film thickness, magnetic field strength, and different HM detection materials. The LSSE signal shows a large enhancement with reductions in temperature, leading to a pronounced peak at low temperatures. We find that the LSSE peak temperature strongly depends on the film thickness as well as on the magnetic field. Our result can be well explained in the framework of magnon-driven LSSE by taking into account the temperature-dependent effective propagation length of thermally excited magnons in the bulk of the material. We further …
Reconstruction of an effective magnon mean free path distribution from spin Seebeck measurements in thin films
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…
Strain-induced improvement of retention loss in PbZr0.2Ti0.8O3 films
The retention behavior of nanoscale domains in PbZr0.2Ti0.8O3 thin films is investigated by in-situ controlling the epitaxial strain arising from a piezoelectric substrate. The retention behavior in our sample shows strong polarity-dependence: Upward-poled domains exhibit excellent stability, whereas downward-poled domains reveal a stretched exponential decay. Reversible release of in-plane compressive strain strongly reduced the retention loss, reflected in an enhancement of the relaxation time by up to one order of magnitude. We tentatively attribute the observed behavior to a strain dependence of the built-in field at the interface to the La0.7Sr0.3MnO3 bottom electrode, with a possible …
Magnetic field control of the spin Seebeck effect
The origin of the suppression of the longitudinal spin Seebeck effect by applied magnetic fields is studied. We perform numerical simulations of the stochastic Landau-Lifshitz-Gilbert equation of motion for an atomistic spin model and calculate the magnon accumulation in linear temperature gradients for different strengths of applied magnetic fields and different length scales of the temperature gradient. We observe a decrease of the magnon accumulation with increasing magnetic field and we reveal that the origin of this effect is a field dependent change of the frequency distribution of the propagating magnons. With increasing field the magnonic spin currents are reduced due to a suppressi…
Multiferroic BiFeO<inf>3</inf> for conductance control at the LaAlO<inf>3</inf>/SrTiO<inf>3</inf>-interface
Multiferroic materials possessing both magnetic and ferroelectric order enable in principle to switch order parameters using not the direct reciprocal field, e.g. to switch the magnetization by an electric field or the electric polarization by a magnetic field. A recent breakthrough was achieved by the demonstration of the ferromagnetic switching of a Co layer with an electric field employing the multiferroic BiFeO 3 [1]. The latter material is a perovskite based oxide that shows stable ferro-electricity as well as an antiferromagnetic order at room temperature [2,3]. Due to a Dzyaloshinskii-Moriya interaction induced by rotation of oxygen octahedra leading to noncollinear Fe-O-Fe bonds a s…
Length Scale of the Spin Seebeck Effect
We investigate the origin of the spin Seebeck effect in yttrium iron garnet (YIG) samples for film thicknesses from 20 nm to 50 μm at room temperature and 50 K. Our results reveal a characteristic increase of the longitudinal spin Seebeck effect amplitude with the thickness of the insulating ferrimagnetic YIG, which levels off at a critical thickness that increases with decreasing temperature. The observed behavior cannot be explained as an interface effect or by variations of the material parameters. Comparison to numerical simulations of thermal magnonic spin currents yields qualitative agreement for the thickness dependence resulting from the finite magnon propagation length. This allow…
High-sensitive switchable photodetector based on BiFeO3 film with in-plane polarization
A high-sensitive and fast-response photodetector based on BiFeO3 (BFO) ferroelectric thin film is fabricated using coplanar electrode configuration. A large photocurrent/dark current ratio is found up to two orders of magnitude at 1 V bias. Enhanced photocurrent and rectification behavior of the photodetector are observed after applying high voltage pulses to the BFO film. The short-circuit current varies systematically with the poling process and increases linearly with the light density. On the contrary, the open-circuit voltage keeps as a constant during the measurements. We attribute these behaviors to the depolarization field and the interfacial fields at the film-electrode interfaces.…
Strain dependence of antiferromagnetic interface coupling in La0.7Sr0.3MnO3/SrRuO3 superlattices
We have investigated the magnetic response of La0.7Sr0.3MnO3/SrRuO3 superlattices to biaxial in-plane strain applied in-situ. Superlattices grown on piezoelectric substrates of 0.72PbMg1/3Nb2/3O3-0.28PbTiO3(001) (PMN-PT) show strong antiferromagnetic coupling of the two ferromagnetic components. The coupling field of mu0HAF = 2.8 T is found to decrease by deltaHAF/delta epsilon ~ -520 mT %-1 under reversible biaxial strain mu0HAF at 80 K in a [La0.7Sr0.3MnO3(22)/SrRuO3(55)]15 superlattice. This reveals a significant strain effect on interfacial coupling. The applied in-plane compression enhances the ferromagnetic order in the manganite layers which are under as-grown tensile strain. It is t…
Magnon mode selective spin transport in compensated ferrimagnets
We investigate the generation of magnonic thermal spin currents and their mode selective spin transport across interfaces in insulating, compensated ferrimagnet/normal metal bilayer systems. The spin Seebeck effect signal exhibits a non-monotonic temperature dependence with two sign changes of the detected voltage signals. Using different ferrimagnetic garnets, we demonstrate the universality of the observed complex temperature dependence of the spin Seebeck effect. To understand its origin, we systematically vary the interface between the ferrimagnetic garnet and the metallic layer, and by using different metal layers we establish that interface effects play a dominating role. They do not …
Spin Hall magnetoresistance in the non-collinear ferrimagnet GdIG close to the compensation temperature
We investigate the spin Hall magnetoresistance (SMR) in a gadolinium iron garnet (GdIG)/platinum (Pt) heterostructure by angular dependent magnetoresistance measurements. The magnetic structure of the ferromagnetic insulator GdIG is non-collinear near the compensation temperature, while it is collinear far from the compensation temperature. In the collinear regime, the SMR signal in GdIG is consistent with the usual [Formula: see text] relation well established in the collinear magnet yttrium iron garnet, with [Formula: see text] the angle between magnetization and spin Hall spin polarization direction. In the non-collinear regime, both an SMR signal with inverted sign and a more complex an…
Thermal generation of spin current in epitaxial CoFe2O4 thin films
The longitudinal spin Seebeck effect (LSSE) has been investigated in high-quality epitaxial CoFe2O4 (CFO) thin films. The thermally excited spin currents in the CFO films are electrically detected in adjacent Pt layers due to the inverse spin Hall effect (ISHE). The LSSE signal exhibits a linear increase with increasing temperature gradient, yielding a LSSE coefficient of ~100 nV/K at room temperature. The temperature dependence of the LSSE is investigated from room temperature down to 30 K, showing a significant reduction at low temperatures, revealing that the total amount of thermally generated magnons decreases. Furthermore, we demonstrate that the spin Seebeck effect is an effective to…