arXiv subjects

Denise Hinzke

Publications and source records attributed to Denise Hinzke.

7 recordsLinked to original sources

arXiv2018

Roles of heating and helicity in ultrafast all-optical magnetization switching in TbFeCo

Using time-resolved magneto-optical Kerr effect (TR-MOKE) method, helicity-dependent all-optical magnetization switching (HD-AOS) is observed in ferrimagnetic TbFeCo films. The thermal effect and opto-magneto effects are separately justified after single circularly polarized laser pulse. The integral evolution of this ultrafast switching is characterized on different time scales and the defined magnetization reversal time of 460 fs is the fastest ever observed. Combining the heat effect and inverse Faraday effect (IFE), micromagnetic simulations based on a single macro-spin model are performed that reproduce HD-AOS following a linear reversal mechanism.

cond-mat.mtrl-sci↗

arXiv2017

Modeling ultrafast all-optical switching in synthetic ferrimagnets

Based on numerical simulations, we demonstrate thermally induced magnetic switching in synthetic ferrimagnets composed of multilayers of rare-earth and transition metals. Our findings show that deterministic magnetization reversal occurs above a certain threshold temperature if the ratio of transition metal atoms to rare-earth atoms is sufficiently large. Surprisingly, the total thickness of the multilayer system has little effect on the occurence of switching. We further provide a simple argument to explain the temperature dependence of the reversal process.

cond-mat.mes-hall↗

arXiv2016

Thermally induced magnon accumulation in two-sublattice magnets

We present a temperature dependent study of the thermal excitation of magnonic spin currents in two-sublattice magnetic materials. Using atomistic spin model simulations, we study the local magnetization profiles in the vicinity of a temperature step in antiferromagnets, as well as in ferrimagnets. It is shown that the strength of the excitation of the spin currents in these systems scales with the derivative of the magnetization with respect to the temperature.

cond-mat.mtrl-sci↗

arXiv2016

Propagation of Thermally Induced Magnonic Spin Currents

The propagation of magnons in temperature gradients is investigated within the framework of an atomistic spin model with the stochastic Landau-Lifshitz-Gilbert equation as underlying equation of motion. We analyze the magnon accumulation, the magnon temperature profile as well as the propagation length of the excited magnons. The frequency distribution of the generated magnons is investigated in order to derive an expression for the influence of the anisotropy and the damping parameter on the magnon propagation length. For soft ferromagnetic insulators with low damping a propagation length in the range of some $μ$m can be expected for exchange driven magnons.

cond-mat.mtrl-sci↗

arXiv2015

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 suppression of parts of the frequency spectrum. By comparison with measurements of the magnetic field dependent longitudinal spin Seebeck effect in YIG thin films with various thicknesses, we find that our model describes the experimental data very well, demonstrating the importance of this effect for experimental systems.

cond-mat.mtrl-sci↗

arXiv2014

Temperature Dependent Ferromagnetic Resonance via the Landau-Lifshitz-Bloch Equation: Application to FePt

Using the Landau-Lifshitz-Bloch (LLB) equation for ferromagnetic materials, we derive analytic expressions for temperature dependent absorption spectra as probed by ferromagnetic resonance (FMR). By analysing the resulting expressions, we can predict the variation of the resonance frequency and damping with temperature and coupling to the thermal bath. We base our calculations on the technologically relevant L1$_0$ FePt, parameterised from atomistic spin dynamics simulations, with the Hamiltonian mapped from ab-initio parameters. By constructing a multi-macrospin model based on the LLB equation and exploiting GPU acceleration we extend the study to investigate the effects on the damping and resonance frequency in $μ$m sized structures.

cond-mat.mtrl-sci↗

arXiv2013

Determination of the origin of the spin Seebeck effect - bulk vs. interface effects

The observation of the spin Seebeck effect in insulators has meant a breakthrough for spin caloritronics due to the unique ability to generate pure spin currents by thermal excitations in insulating systems without moving charge carriers. Since the recent first observation, the underlying mechanism and the origin of the observed signals have been discussed highly controversially. Here we present a characteristic dependence of the longitudinal spin Seebeck effect amplitude on the thickness of the insulating ferromagnet (YIG). Our measurements show that the observed behavior cannot be explained by any effects originating from the interface, such as magnetic proximity effects in the spin detector (Pt). Comparison to theoretical calculations of thermal magnonic spin currents yields qualitative agreement for the thickness dependence resulting from the finite effective magnon propagation length so that the origin of the effect can be traced to genuine bulk magnonic spin currents ruling out parasitic interface effects.

cond-mat.mtrl-sci↗