arXiv subjects

Richard Schlitz

Publications and source records attributed to Richard Schlitz.

At least 19 recordsLinked to original sources

arXiv2026

Coherent and Dissipative Spin Torques in Quantum Dots: A Unified Framework for Quantum Spin Dynamics

The manipulation of single spins through spin-polarized tunneling opens new routes for quantum control at the atomic scale. We present a theoretical framework describing spin-transfer, spin torques and spin resonance in molecular quantum dots weakly coupled to magnetic electrodes. By deriving a Lindblad master equation from microscopic tunneling processes, we capture both coherent exchange interactions and dissipative spin torque effects within a unified approach. We analyze how charge transport through localized orbitals influences spin dynamics and show that modulating the tunneling rates in time can induce electron spin resonance. This framework is further extended to coupled spin systems, revealing how spin coherence and entanglement respond to local spin torques and highlighting sources of transport-driven decoherence. Our results provide a general model to interpret spin-resolved tunneling experiments and extend classical spin torque concepts into the quantum regime.

cond-mat.mes-hall↗

arXiv2026

Coherent Microwave Driving of Domain Wall Depinning in a Ferrimagnetic Garnet

Coherent control of domain wall dynamics offers a route to fast manipulation of magnetic textures beyond thermally activated motion. We demonstrate resonant excitation of linear and nonlinear dynamics of a pinned domain wall in a ferrimagnetic garnet thin film driven by a microwave field. Using scanning nitrogen-vacancy magnetometry and nonlocal spin-pumping measurements, we identify a low-frequency mode inside the magnon gap, originating from the localized oscillatory motion of a domain wall across a pinning line defined by a Pt stripline. Upon increasing the microwave drive into the nonlinear regime, this mode enables domain wall depinning at reduced external magnetic fields. Micromagnetic simulations reveal a progression from localized oscillations to partial relocation between pinning sites and, ultimately, complete escape from the pinning region with increasing driving power. These results establish resonant excitation of domain walls at engineered pinning sites as a mechanism for manipulating magnetic textures via localized nonlinear dynamics.

cond-mat.mes-hall↗

arXiv2026

Disambiguating electrical detection of magnetization dynamics in magnetic insulators

Electrical detection of magnetization dynamics in magnetic insulators underpins both fundamental studies of magnon transport and the development of low-loss magnonic devices. In heavy-metal/magnetic-insulator heterostructures, spin pumping and spin-torque ferromagnetic resonance (ST-FMR) are widely used for this purpose and are often treated separately in different measurement geometries. In practice, the competition between these two effects gives rise to electrical voltage signals of opposite signs, which can lead to ambiguous interpretations of the underlying physics. Here, we show how to disambiguate their respective contributions and provide a framework for interpreting experiments involving microwave excitation of magnetic insulators and detection of magnetization dynamics via spin-charge conversion in heavy metals. We systematically investigate spin pumping and ST-FMR in nonlocal and local devices using Pt-capped thin films of thulium and bismuth-yttrium iron garnets. We show how spin-wave character, magnetic dissipation, magnetic field orientation and device geometry govern the sign and magnitude of the resulting signals. In several cases, the voltage generated by microwave excitation changes sign between an out-of-plane or in-plane magnetic configuration. We disentangle a contribution due to spin pumping, induced by exponentially decaying propagating spin waves, and a weakly distance-dependent contribution from ST-FMR, remotely induced by inductive coupling. We show that both the spin wave excitation profile across the film thickness and magnetic damping largely determine which of the two contributions dominates. Hence, the sign of the electrical signal cannot be uniquely assigned to the chirality of the magnon modes.

cond-mat.mes-hall↗

arXiv2026

Loop-gap resonators achieving strong magnon-photon coupling in magnetic insulator thin films

Magnon-photon hybrid systems consisting of a three-dimensional electromagnetic resonator and a bulk magnetic insulator constitute the standard experimental platform in cavity magnonics. Here, we demonstrate a modular loop-gap resonator design optimized to couple with thin films of magnetic insulators. We achieve the strong-coupling regime using this loop-gap resonator coupled to a 75~nm-thick epitaxial film of yttrium iron garnet at room temperature. We further show how to perform field-differential spectroscopy of the hybrid magnon-photon system, which eliminates the unwanted signal from other loop-gap modes uncoupled to the magnetic film. In addition to the uniform ferromagnetic resonance mode, the loop-gap resonator enables an hybridization with the standing spin-wave modes forming across the thickness of the film. Our approach unlocks the use of epitaxial films and multilayers of magnetic insulators to tune the magnon band structure in cavity magnonics experiments.

cond-mat.mes-hall↗

arXiv2026

Magnon Kerr effect in a magnetic thin film strongly coupled to a microwave resonator

Cavity magnonics investigates hybrid systems where magnons interact coherently with photons, providing a platform to harness light-matter interaction in magnetic materials. Progress in this field hinges on achieving stronger and tunable nonlinear effects, which are essential for controlling magnon dynamics and frequency conversion. Here, we demonstrate the magnon Kerr effect in an anisotropic magnonic system comprising a 200~nm-thick yttrium iron garnet film strongly coupled to a three-dimensional microwave resonator. The strong shape anisotropy significantly enhances the magnon Kerr effect compared to a sphere of equivalent volume, while the cavity enables sensitive probing of magnetization dynamics. We demonstrate continuous tunability of the magnitude and sign of the Kerr shift by controlling the static orientation of the magnetization. Input-output modeling of the magnon-photon interaction provides a consistent description of our system and Kerr coefficients matching the experimental results. Our findings demonstrate a scalable approach to enhancing Kerr anharmonicity in hybrid magnon-photon systems while preserving strong coupling.

cond-mat.mes-hall↗

arXiv2026

Direct Observation of Antimagnons with Inverted Dispersion

We report direct spectroscopic evidence of antimagnons, i.e., negative-energy spin waves identified by their signature inverted dispersion and left-handed precession with Brillouin light scattering (BLS) spectroscopy. We investigate an ultrathin BiYIG film with a perpendicular magnetized anisotropy that compensates the demagnetizing field. By injecting a spin-orbit torque, the magnetization is driven into auto-oscillation and eventually into a non-equilibrium reversed state above a secondary current threshold ($\sim$1.2$\times$10$^7$~A/cm$^2$). The dispersion is measured by wavevector-resolved BLS and exhibits a sharp change from an upward dispersion to a downward one, in agreement with theoretical predictions and micromagnetic simulations. Around the threshold current, we observe the coexistence of conventional magnons and antimagnons. Our work establishes antimagnons with inverted dispersion and is a first step towards exploring novel phenomena and applications due to magnon-antimagnon coupling, such as magnon amplification and magnon-antimagnon entanglement, which are part of the emerging field of antimagnonics.

cond-mat.mes-hall↗

arXiv2026

Dynamical Stabilization of Inverted Magnetization and Antimagnons by Spin Injection in an Extended Magnetic System

Dynamical perturbations can modify the energy landscape of a physical system, such that unstable equilibrium configurations become stable when subject to an external drive. The magnetic analog of such dynamical stabilization corresponds to saturation of the magnetization against an external field. Here we report dynamical stabilization of the magnetization in thin film bismuth-substituted yttrium iron garnet by spin current injection from an adjacent Pt layer. Magneto-optical Kerr effect measurements demonstrate magnetization reversal against magnetic fields up to 3000 times larger than the film's coercivity once the spin injection surpasses a critical threshold associated with negative damping. Micromagnetic simulations reveal that this process is mediated by the excitation of a large population of incoherent magnons with non-zero wave vector, leading to a transient shortening and subsequent stabilization of the inverted magnetization. The elementary excitations of the high-energy inverted magnetization state are shown to be antimagnons, quasi-particles carrying opposite energy and spin relative to magnons. Our results further reveal how the system's size and minimization of nonlinear magnon scattering processes play a key role in dynamical stabilization, opening new avenues for magnetic state control beyond conventional magnetization switching. Dissipation-driven phase transitions in large-area magnetic systems provide a solid-state platform to study magnonic analogs of relativistic phenomena, such as Klein tunneling and black holes, as well as spin-wave amplification and lasing.

cond-mat.mes-hall↗

arXiv2026

Ultrathin bismuth-yttrium iron garnet films with tunable magnetic anisotropy

We report on the epitaxial growth of nm-thick films of bismuth-substituted yttrium iron garnet (BiYIG) by high-temperature off-axis radio-frequency magnetron sputtering. We demonstrate accurate control of the magnetic properties by tuning of the sputtering parameters and epitaxial strain on various (111)-oriented garnet substrates. BiYIG films with up to -0.80\% lattice mismatch with the substrate remain fully strained up to 60~nm-thick, maintaining a high crystalline quality. Transmission electron microscopy and energy-dispersive X-ray spectroscopy confirm coherent epitaxial growth, the absence of defects, and limited interdiffusion at the BiYIG/substrate interface. Varying the tensile or compressive strain between -0.80\% and +0.56\% in BiYIG allows for accurate compensation of the total magnetic anisotropy through magneto-elastic coupling. The effective magnetic anisotropy of sputtered BiYIG films can be further tuned via the off-axis deposition angle and the oxygen flow during growth, which determine the cation stoichiometry. Under optimized growth conditions, a ferromagnetic resonance (FMR) linewidth of 1~mT at 10~GHz is reliably obtained even for thicknesses as low as 10~nm. We also report small FMR linewidths in ultrathin (2-5~nm) BiYIG films grown on diamagnetic substrate yttrium scandium gallium garnet. These findings highlight the promise of low-damping, strain-engineered nm-thick BiYIG films for implementing advanced functionalities in spin-orbitronic and magnonic devices. Specifically, the magnetic-anisotropy compensation and low damping enable large cone-angle magnetization dynamics immune to magnon-magnon nonlinear scattering.

cond-mat.mtrl-sci↗

arXiv2025

Statistical characterization of the spin Hall magnetoresistance in YIG/Pt heterostructures

The spin Hall magnetoresistance (SMR) is widely used to study the interplay between charge and spin currents in bilayers of a magnetic insulator and a normal metal. However, not much is known about the spatial variation of the SMR across the surface of one and the same sample. In this work, we investigate the statistical distribution of the SMR in hundreds of nominally identical Hall bar structures patterned into prototypical yttrium iron garnet (YIG)/Pt heterostructures. We find a Gaussian-distributed SMR with a narrow standard deviation of approximately 10$\,$% of the mean value in each YIG/Pt bilayer studied. However, the variation of the mean SMR between different YIG/Pt samples can be as large as ~30$\,$%, despite nominally identical fabrication conditions. This demonstrates that spatial variations of the SMR amplitude must not be neglected, in particular when comparing different heterostructures. On a microscopic level, local variations of the interface quality captured by the spin mixing conductance are the most likely origin for the observed SMR amplitude variations.

cond-mat.mtrl-sci↗

arXiv2025

Low-temperature-compatible iron garnet films grown by liquid phase epitaxy

Single-crystalline yttrium iron garnet (YIG) thin films (< 100 nm) form the backbone of magnonics, owing to the record-low losses affecting their magnetization dynamics. However, thin epitaxial YIG has mostly been investigated under ambient temperatures, limited by the paramagnetic losses occurring at low temperatures due to the gadolinium gallium garnet (GGG) substrates required for epitaxial growth. Driven by a growing interest in magnonic devices that can operate in cryogenic conditions and address quantum information applications, there is a strong need for iron garnet epitaxial films grown on diamagnetic substrates that can maintain low losses at low temperatures. In this work, we use liquid phase epitaxy (LPE) to grow ultrathin films of strained YIG on a commercial diamagnetic substrate, yttrium scandium gallium garnet (YSGG). We investigate their magnetization dynamics in the 3-300 K temperature range, and compare them to equivalent films grown on paramagnetic GGG. We demonstrate for LPE YIG on YSGG substrates a ferromagnetic resonance linewidth below 1 mT at 3 K, together with a very weak temperature and frequency dependence of the losses. The growth of YIG/YSGG by LPE provides a straightforward approach to producing iron garnet thin films for use in low-temperature investigations.

cond-mat.mtrl-sci↗

arXiv2025

Current-Controlled Magnon-Magnon Coupling in an On-Chip Cavity Resonator

Harnessing spin currents to control magnon dynamics enables new functionalities in magnonic devices. Here, we demonstrate current-controlled magnon-magnon coupling between cavity and boundary modes in an ultrathin film of Bi-doped yttrium iron garnet (BiYIG). Cavity modes emerge in a BiYIG region between two Pt nanostripes, where interfacial anisotropy modifies the magnon dispersion. These modes hybridize with boundary magnons confined within the Pt-capped BiYIG, resulting in an anticrossing gap. Modeling based on dipole-exchange spin-wave dispersion accurately reproduces the observed modes and their hybridization. Spin current injection via the spin Hall effect in a Pt nanostripe disrupts the cavity boundary conditions and suppresses both cavity modes and hybridization upon driving the system beyond the damping compensation threshold. Furthermore, tuning the microwave power applied to a microstrip antenna enables controlled detuning of the anticrossing gap. Our findings provide a platform for exploring spin current-magnon interactions and designing on-chip reconfigurable magnonic devices.

cond-mat.mes-hall↗

arXiv2025

Orbital Pumping in Ferrimagnetic Insulators

We report the detection of pure orbital currents generated by both coherent and thermal magnons in the magnetic insulator Bi-doped yttrium iron garnet (BiYIG). The pumping of orbital and spin currents is jointly investigated in nano-devices made of naturally oxidized Cu, pure Cu, Pt, and Cr. The absence of charge conduction in BiYIG and the negligible spin-to-charge conversion of oxidized Cu allows us to disambiguate the orbital current contribution. Comparative measurements on YIG and BiYIG show that the origin of the orbital pumping in BiYIG/oxidized Cu is the dynamics of the orbital magnetization in the magnetic insulator. In Cr, the pumping signal is dominated by the negative spin Hall effect rather than the positive orbital Hall effect, indicating that orbital currents represent a minority of the total angular momentum current pumped from the magnetic insulator. Our results also evidence that improving the interfacial transparency significantly enhances pumping efficiencies not only for spin, but also for orbital currents.

cond-mat.mes-hall↗

arXiv2025

Magnetic aftereffect and Barkhausen effect in thin films of the altermagnetic candidate Mn5Si3

Altermagnetism as a third distinct type of collinear magnetic ordering lately attracts vivid attention. We here study the Hall effect response of micron-scale Hall bars patterned into Mn5Si3 thin films, an altermagnet candidate material. Recording transport data as a function of time, at fixed magnetic field magnitude, we observe a time-dependent relaxation of the Hall voltage qualitatively and quantitatively similar to the magnetic viscosity response well established in ferromagnetic films. In addition, the Hall voltage time traces feature clear unilateral steps, which we interpret as Barkhausen steps, i.e., as experimental evidence for abrupt reorientations of magnetic (Hall vector) domains in the altermagnetic candidate material. A quantitative analysis yields a Barkhausen length of around 18nm in the Hall bar devices with the smallest width of 100 nm.

cond-mat.mtrl-sci↗

arXiv2024

Estimation of spin-orbit torques in the presence of current-induced magnon creation and annihilation

We present a comprehensive set of harmonic resistance measurements of the dampinglike (DL) and fieldlike (FL) torques in Pt/CoFeB, Pt/Co, W/CoFeB, W/Co, and YIG/Pt bilayers complemented by measurements of the DL torque using the magneto-optical Kerr effect and calibrated by nitrogen vacancy magnetometry on the same devices. The magnon creation-annihilation magnetoresistances depend strongly on temperature and on the magnetic and transport properties of each bilayer, affecting the estimate of both the DL and FL torque. The DL torque, the most important parameter for applications, is overestimated by a factor of 2 in W/CoFeB and by one order of magnitude in YIG/Pt when not accounting for the magnonic contribution to the planar Hall resistance. We further show that the magnonic contribution can be quantified by combining measurements of the nonlinear longitudinal and transverse magnetoresistances, thus providing a reliable method to measure the spin-orbit torques in different material systems.

cond-mat.mes-hall↗

arXiv2024

Nonlinear longitudinal and transverse magnetoresistances due to current-induced magnon creation-annihilation processes

Charge-spin conversion phenomena such as the spin Hall effect allow for the excitation of magnons in a magnetic layer by passing an electric current in an adjacent nonmagnetic conductor. We demonstrate that this current-induced modification of the magnon density generates an additional nonlinear longitudinal and transverse magnetoresistance for every magnetoresistance that depends on the magnetization. Using harmonic measurements, we evidence that these magnon creation-annihilation magnetoresistances dominate the second harmonic longitudinal and transverse resistance of thin Y$_{3}$Fe$_{5}$O$_{12}$/Pt bilayers. Our results apply to both insulating and metallic magnetic layers, elucidating the dependence of the magnetoresistance on applied current and magnetic field for a broad variety of systems excited by spin currents.

cond-mat.mes-hall↗

arXiv2024

Altermagnetic variants in thin films of Mn5Si3

The altermagnet candidate Mn5Si3 has attracted wide attention in the context of non-relativistic spin physics, due to its composition of light elements. However, the presumed structure of the altermagnetic phase had yet to be demonstrated. In this study, we demonstrate a hallmark of altermagnetism in Mn5Si3 thin films, namely the three options, or variants, for the checkerboard distribution of the magnetic Mn atoms. The magnetic symmetries were altered by field-rotation of the Néel vector along relevant crystal directions, resulting in anomalous Hall effect anisotropy. The experimental results in nanoscale devices were corroborated by a theoretical model involving atomic site dependent anisotropy and bulk Dzyaloshinskii-Moriya interaction for a single variant.

cond-mat.mes-hall↗

arXiv2024

Competing Ordinary and Hanle Magnetoresistance in Pt and Ti Thin Films

One of the key elements in spintronics research is the spin Hall effect, allowing to generate spin currents from charge currents. A large spin Hall effect is observed in materials with strong spin orbit coupling, e.g., Pt. Recent research suggests the existence of an orbital Hall effect, the orbital analogue to the spin Hall effect, which also arises in weakly spin orbit coupled materials like Ti, Mn or Cr. In Pt both effects are predicted to coexist. In any of these materials, a magnetic field perpendicular to the spin or orbital accumulation leads to additional Hanle dephasing and thereby the Hanle magnetoresistance (MR). To reveal the MR behavior of a material with both spin and orbital Hall effect, we thus study the MR of Pt thin films over a wide range of thicknesses. Careful evaluation shows that the MR of our textured samples is dominated by the ordinary MR rather than by the Hanle effect. We analyze the intrinsic properties of Pt films deposited by different groups and show that next to the resistivity also the structural properties of the film influence which MR dominates. We further show that this correlation can be found in both spin Hall active materials like Pt and orbital Hall active materials, like Ti. For both materials, the crystalline samples shows a MR attributed to the ordinary MR, whereas we find a large Hanle MR for the samples without apparent structural order. We then provide a set of rules to distinguish between the ordinary and the Hanle MR. We conclude that in all materials with a spin or orbital Hall effect the Hanle MR and the ordinary MR coexist and the purity and crystallinity of the thin film determine the dominating effect.

cond-mat.mtrl-sci↗

arXiv2024

Lattice-tunable substituted iron garnets for low-temperature magnonics

The synthesis of nm-thick epitaxial films of iron garnets by physical vapor deposition has opened up exciting opportunities for the on-chip generation and processing of microwave signals encoded in magnons. However, iron garnet thin films suffer from demanding lattice-matching and stoichiometry requirements. Here a new approach to their synthesis is developed, enabling a precise and continuous tuning of iron garnet compositions based on the co-sputtering of binary oxides. By substituting a controlled proportion of iron with additional yttrium, Y$_{3}$(Y$_{x}$Fe$_{5-x}$)O$_{12}$ films of high crystalline quality are obtained, combining a widely tunable lattice parameter and excellent magnetization dynamics. This enables iron garnet thin films suited for cryogenic applications, which have long remained impractical due to microwave losses caused by paramagnetic garnet substrates. Low-temperature ferromagnetic resonance confirms the elimination of substrate paramagnetic losses for Y$_{3}$(Y$_{x}$Fe$_{5-x}$)O$_{12}$ films lattice-matched to Y$_{3}$Sc$_{2}$Ga$_{3}$O$_{12}$ (YSGG), a diamagnetic substrate. The Y$_{3}$(Y$_{x}$Fe$_{5-x}$)O$_{12}$ system can be matched to other substrates such as (Gd,Y)$_{3}$Sc$_{2}$Ga$_{3}$O$_{12}$. Bi-substituted films of (Bi$_{0.8}$Y$_{2.2}$)Fe$_{5}$O$_{12}$ also have ideal lattice matching to YSGG, demonstrating the versatility of this approach. This opens unprecedented options for cation substitutions in iron garnet films, offering a promising avenue to new properties and quantum magnonic devices operating in low-temperature environments.

cond-mat.mtrl-sci↗