Richard Schlitz

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Schlitz

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Richard

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0000-0001-5756-6716

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Publications 1 - 10 of 16

Lattice-tunable Substituted Iron Garnets for Low-temperature Magnonics
Legrand, William; Kemna, Yana; Schären, Stefan; et al. (2025)
Advanced Functional Materials
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, Y3(YxFe5–x)O12 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 Y3(YxFe5–x)O12 films lattice-matched to Y3Sc2Ga3O12 (YSGG), a diamagnetic substrate. The Y3(YxFe5–x)O12 system can be matched to other substrates such as (Gd, Y)3Sc2Ga3O12. Bi-substituted films of (Bi0.8Y2.2)Fe5O12 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.
Nonlocal magnon transconductance in extended magnetic insulating films. II. Two-fluid behavior
Kohno, Ryuhei; An, K.; Clot, E.; et al. (2023)
Physical Review B
This paper presents a comprehensive study of the spatial dispersion of propagating magnons electrically emitted in extended yttrium-iron garnet (YIG) films by the spin transfer effects across a YIG|Pt interface. Our goal is to provide a generic framework to describe the magnon transconductance inside magnetic films. We experimentally elucidate the relevant spectral contributions by studying the lateral decay of the magnon signal. While most of the injected magnons do not reach the collector, the propagating magnons can be split into two fluids: (i) a large fraction of high-energy magnons carrying energy of about kBT0, where T0 is the lattice temperature, with a characteristic decay length in the submicrometer range, and (ii) a small fraction of low-energy magnons, which are particles carrying energy of about ℏωK, where ωK/(2π) is the Kittel frequency, with a characteristic decay length in the micrometer range. Taking advantage of their different physical properties, the low-energy magnons can become the dominant fluid (i) at large spin transfer rates for the bias causing the emission of magnons, (ii) at large distance from the emitter, (iii) at small film thickness, or (iv) for reduced band mismatch between the YIG below the emitter and the bulk due to variation of the magnon concentration. This broader picture complements a companion paper [R. Kohno, Phys. Rev. B 108, 144410 (2023)10.1103/PhysRevB.108.144410], which focuses solely on the nonlinear transport properties of low-energy magnons.
Nonlinear Longitudinal and Transverse Magnetoresistances due to Current-Induced Magnon Creation-Annihilation Processes
Noël, Paul; Schlitz, Richard; Karadža, Emir; et al. (2025)
Physical Review Letters
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 Y3Fe5O12/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.
Competing ordinary and Hanle magnetoresistance in Pt and Ti thin films
Sailler, Sebastian; Sala, Giacomo; Reustlen, Denise; et al. (2025)
Physical Review B
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 analog 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 first 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, we find a large Hanle MR for the samples without apparent structural order, whereas the ordinary MR dominates in the crystalline samples. We then provide a set of rules to distinguish between the ordinary and the Hanle MR. We suggest that in all materials with a spin or orbital Hall effect the Hanle MR and the ordinary MR coexist and the purity, crystallinity, and electronic structure of the thin film determine the dominating effect.
Auto-oscillations and directional magnon emission induced by spin current injection into large magnetic volumes
Schlitz, Richard; Demidov, Vladislav E.; Lammel, Michaela; et al. (2025)
Nature Communications
The ability to manipulate magnons using electronic currents holds transformative potential for high-frequency signal processing architectures based on insulating magnetic materials. A critical challenge, however, lies in achieving efficient magnon emission and amplification through damping compensation, which typically requires ultra-thin films. In this study, we break this limitation by demonstrating a three-order-of-magnitude increase in magnon population, consistent with the onset of auto-oscillations upon reaching damping compensation, by injecting a spin current from a μm-wide Pt wire into a continuous 150 nm-thick yttrium iron garnet film. Using nonlocal magnon transport and Brillouin light scattering, we reveal that damping compensation occurs due to magnon self-localization beneath the Pt injector, which precludes radiation from the excited region. As a result, the nonlocal magnon conductance becomes mode-dependent and is significantly amplified by multi-magnon scattering at high magnon populations. Finally, we demonstrate that interfacial spin injection breaks yttrium iron garnet’s inversion symmetry, leading to unidirectional magnon emission. Our results pave the way for the development of advanced magnonic devices, including directional magnon emitters, and offer a new approach to achieving damping compensation in thick magnetic films.
Current-Controlled Magnon-Magnon Coupling in an On-Chip Cavity Resonator
Wang, Hanchen; Legrand, William; Schlitz, Richard; et al. (2025)
Nano Letters
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.
Implementation of field-differential phase-resolved microwave magnetic spectroscopy
Legrand, William; Petrosyan, Davit; Wang, Hanchen; et al. (2025)
Review of Scientific Instruments
Microwave spectroscopies are central to the investigation of magnetic systems by enabling the identification of dynamical resonance modes and by providing quantitative information on key magnetic parameters. Experiments on magnetization dynamics based on inductive microwave techniques usually rely on either field-modulated power detection or phase-resolved detection using a vector network analyzer. While these two approaches bring separate advantages, they have rarely been combined together. In this work, we develop customized microwave instrumentation combining phase-resolved detection and magnetic field modulation to perform microwave spectroscopy of magnetic systems. We apply this technique to ferromagnetic resonance (FMR), where it enables a quantitative measurement of the magnetic susceptibility in systems with small volume and magnetization. This method of field-differential phase-resolved microwave magnetic spectroscopy is compared with other approaches and is shown to greatly improve the resolution of finely separated FMR peaks and the detection of small signals. Furthermore, we model and characterize comprehensively the inductive coupling of the magnetic system to the microwave circuit, which enables a quantitative analysis of the resonance peaks and the rejection of potential errors originating from too strong permeability, imperfect impedance matching, broadening induced by field inhomogeneity, and varying sample placement.
Estimation of spin-orbit torques in the presence of current-induced magnon creation and annihilation
Noël, Paul; Karadža, Emir; Schlitz, Richard; et al. (2025)
Physical Review B
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.
Orbital Pumping in Ferrimagnetic Insulators
Wang, Hanchen; Kang, Min-Gu; Petrosyan, Davit; et al. (2025)
Physical Review Letters
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 nanodevices 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.
Nonlinear longitudinal and transverse magnetoresistances due to current-induced magnon creation-annihilation processes
Noël, Paul; Schlitz, Richard; Karadža, Emir; et al. (2024)
arXiv
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 Y3Fe5O12/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.

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