Resonance In Yttrium Iron Garnet Research Articles

Quantum paradigm of the foldover magnetic resonance

The explosive development of quantum magnonics requires the consideration of several previously known effects from a new angle. In particular, taking into account the quantum behavior of magnons is essential at high excitations of the magnetic system, under the conditions of the so-called phenomenon of “foldover” (bi-stable) magnetic resonance. Previously, this effect was considered in the quasi-classical macrospin approximation. However, at large angles of magnetization precession, the magnon density exceeds the critical value for the formation of a magnon Bose condensate (mBEC). Naturally, this purely quantum phenomenon does not exist in the classical approximation. In addition, mBEC leads to superfluid transfer of magnetization, which suppresses the macroinhomogeneity of the samples. The experiments presented in the article show that quantum phenomena well describes the experimental results of nonlinear magnetic resonance in yttrium iron garnet. Thus, we remove the questions that arose earlier when considering this effect without taking into account quantum phenomena. This discovery paves the way for many quantum applications of supermagnonics, such as the magnetic Josephson effect, long-range spin transport, Q-bits, quantum logic, magnetic sensors, and others.

Observation of terahertz magnon of Kaplan-Kittel exchange resonance in yttrium-iron garnet by Raman spectroscopy

Backscattering Raman spectroscopic investigations were performed on an yttrium-iron garnet single crystal using linearly and circularly polarized light. A terahertz (THz) magnon of the Kaplan-Kittel (KK) exchange resonance was discovered, which had been regarded as unobservable via optical methods. The KK exchange resonance had a 7.8-THz frequency at 80 K, and the polarization selection rule led to an antisymmetric Raman tensor of the $A_{2}$ mode. Moreover, the assignment of all the Raman-active phonon modes, $3A_{1g}$, $8E_{g}$, and $14T_{2g}$, was proposed. This study will stimulate further investigation of the coupling of THz magnons and phonons and pave the way toward THz optomagnonics.

Octave-Tunable Magnetostatic Wave YIG Resonators on a Chip.

We have designed, fabricated, and characterized magnetostatic wave (MSW) resonators on a chip. The resonators are fabricated by patterning single-crystal yttrium iron garnet (YIG) film on a gadolinium gallium garnet (GGG) substrate and excited by loop-inductor transducers. We achieved this technology breakthrough by developing a YIG film etching process and fabricating thick aluminum coplanar waveguide (CPW) inductor loop around each resonator to individually address and excite MSWs. At 4.77 GHz, the 0.68-mm2 resonator achieves a quality factor ( with a bias field of 987 Oe. We also demonstrate YIG resonator tuning by more than one octave from 3.63 to 7.63 GHz by applying an in-plane external magnetic field. The measured quality factor of the resonator is consistently over 3000 above 4 GHz. The micromachining technology enables the fabrication of multiple single- and two-port YIG resonators on the same chip with all resonators demonstrating octave tunability and high Q .

Simultaneous spin pumping and spin Seebeck experiments with thermal control of the magnetic damping in bilayers of yttrium iron garnet and heavy metals: YIG/Pt and YIG/IrMn

We report experiments on the generation of spin currents by simultaneous spin pumping effect and spin Seebeck effect (SSE) in bilayers of yttrium iron garnet (YIG)/Pt and YIG/IrMn. The experiments are performed with the ferromagnetic resonance (FMR) in YIG excited by microwave radiation in the range of 2--6 GHz and subject to a temperature gradient as in studies of the longitudinal SSE. Measurements of the FMR linewidth show that the magnetic damping in YIG can be controlled by spin currents generated by the thermal gradient across the thickness of the bilayer. The simultaneous measurements allow the determination of the spin current generated by SSE and a quantitative comparison of the models proposed for thermal control of the magnetic damping with experimental data. We show that the model based on the flow of angular momentum into or out of the YIG film carried by the coherent part of the spin current influenced by the temperature gradient is the one that best accounts for the observed change in the damping.

Spin transport in antiferromagnetic NiO and magnetoresistance in Y3Fe5O12/NiO/Pt structures

We have studied spin transport and magnetoresistance in yttrium iron garnet (YIG)/NiO/Pt trilayers with varied NiO thickness. To characterize the spin transport through NiO we excite ferromagnetic resonance in YIG with a microwave frequency magnetic field and detect the voltage associated with the inverse spin-Hall effect (ISHE) in the Pt layer. The ISHE signal is found to decay exponentially with the NiO thickness with a characteristic decay length of 3.9 nm. This is contrasted with the magnetoresistance in these same structures. The symmetry of the magnetoresistive response is consistent with spin-Hall magnetoresistance (SMR). However, in contrast to the ISHE response, as the NiO thickness increases the SMR signal goes towards zero abruptly at a NiO thickness of ≃ 4 nm, highlighting the different length scales associated with the spin-transport in NiO and SMR in such trilayers.

Electrodynamic study of YIG filters and resonators.

Numerical solutions of coupled Maxwell and Landau-Lifshitz-Gilbert equations for a magnetized yttrium iron garnet (YIG) sphere acting as a one-stage filter are presented. The filter is analysed using finite-difference time-domain technique. Contrary to the state of the art, the study shows that the maximum electromagnetic power transmission through the YIG filter occurs at the frequency of the magnetic plasmon resonance with the effective permeability of the gyromagnetic medium μr ≈ −2, and not at a ferromagnetic resonance frequency. Such a new understanding of the YIG filter operation, makes it one of the most commonly used single-negative plasmonic metamaterials. The frequency of maximum transmission is also found to weakly depend on the size of the YIG sphere. An analytic electromagnetic analysis of resonances in a YIG sphere is performed for circularly polarized electromagnetic fields. The YIG sphere is situated in a free space and in a large spherical cavity. The study demonstrates that both volume resonances and magnetic plasmon resonances can be solutions of the same transcendental equations.

Nonlinear dynamics of three-magnon process driven by ferromagnetic resonance in yttrium iron garnet

We report an investigation of the dynamics of the three-magnon splitting process associated with the ferromagnetic resonance (FMR) in films of the insulating ferrimagnet yttrium iron garnet (YIG). The experiments are performed with a 6 μm thick YIG film close to a microstrip line fed by a microwave generator operating in the 2–6 GHz range. The magnetization precession is driven by the microwave rf magnetic field perpendicular to the static magnetic field, and its dynamics is observed by monitoring the amplitude of the FMR absorption peak. The time evolution of the amplitude reveals that if the frequency is lowered below a critical value of 3.3 GHz, the FMR mode pumps two magnons with opposite wave vectors that react back on the FMR, resulting in a nonlinear dynamics of the magnetization. The results are explained by a model with coupled nonlinear equations describing the time evolution of the magnon modes.

A MAGNETIC FIELD TUNABLE YTTRIUM IRON GARNET MILLIMETER-WAVE DIELECTRIC PHASE SHIFTER: THEORY AND EXPERIMENT

A magnetically tunable passive narrow-band split-mode mm-wave phase shifter based on dielectric resonance in yttrium iron garnet (YIG) is investigated. The novelty here is the demonstration of a phase shifter in the frequency region between two split dielectric resonances in YIG. It is shown that, under certain conditions, the difierential phase shift from the split modes add up, resulting in a larger phase shift than for a single mode phase shifter. Two prototype phase shifters operating in the U- and W-bands at frequencies much higher than ferromagnetic resonance (FMR) in YIG have been designed and characterized. Phase shifts up to 30 - with low losses and acceptable standing wave ratio are obtained for moderate bias magnetic flelds. Equivalent transmission-line model taking into account coupling between the split resonances is presented and there is reasonable agreement between theory and experiment for both insertion loss and difierential phase shift. Suggestions on further improvements of prototype fllter characteristics have been outlined.

Magnetoelectric microwave attenuator

An electric field tunable yttrium iron garnet (YIG) lead magnesium niobate lead titanate (PMN-PT) attenuator operating at 7.2 GHz has been designed and characterised. The device is based on ferromagnetic resonance in YIG. Electric field (E) tuning of the attenuation has been accomplished through magnetoelectric interactions in the YIG/PMN-PT bilayer. Theoretical estimates of attenuation against E are in very good agreement with data.

Electric field tunable ferrite-ferroelectric hybrid wave microwave resonators: Experiment and theory

The electric field tuning characteristics of a combined microwave resonator based on ferrite-ferroelectric layered structure have been studied in a wide range of bias magnetic fields. The combined ferrite-ferroelectric resonator was composed of two rectangular resonators fabricated from a ceramic barium strontium titanate (BST) slab and a single-crystal yttrium iron garnet (YIG) film. The in-plane dimensions for the YIG and BST resonators were chosen to be equal in order to maximize the electromagnetic coupling between their main modes and reduce spurious influence of their higher order modes. A tuning range of 100MHz for the resonator frequency was realized at 5GHz through the variation of magnetic permeability and dielectric permittivity of the YIG-BST structure. A theory for the hybrid wave excitations, based on a coupled-mode approach, has been developed and provides good description of the data.

Observation of envelope soliton propagation in a new nonlinear transmission line

This letter reports narrowing and splitting of microwave pulses in a new nonlinear transmission line whose elements are yttrium iron garnet resonators. At certain power levels, the observed behavior can be interpreted as envelope solitons.

High resolution spin wave spectroscopy in YIG

It is shown that the ferrimagnetic subsidiary resonance in yttrium iron garnet can be resolved onto hundreds of extremely narrow absorption lines with ΔH ⩾ 0.005 G. They can be identified as standing spin wave modes.

Anisotropic Magnetic Resonance and Relaxation in Silicon-Substituted YIG

The magnetic resonance behavior of silicon-substituted yttrium iron garnet (YIG) crystals having the average ionic composition {Y33+} [Fe1.953+Fe0.052+] (Fe2.953+Si0.054+)O12 has been investigated as a function of temperature and orientation at 9 Gc/sec. Unexpectedly, four extrema were observed in the resonance field Hres at low temperatures. For example, the values of Hres(100)=1575 Oe, Hres(111)=1985 Oe, and Hres (110)=2175 Oe were measured at 77°K. Further measurements at 24 Gc/sec indicated that g=2±0.02 from 300° to 77°K. This inverted anisotropy can be described phenomenologically by an isotropic downward shift of 1260 Oe and the cubic anisotropy fields K1/M0=200 Oe and K2/M0=−540 Oe. These K1>0 and K2<0 values are attributed to the Si4+-induced Fe2+ ions. The enormous isotropic depression of Hres is shown to be predicted by an extended formulation of the ``slow'' relaxation theory. A peak was observed in the resonance linewidth ΔH(100) of 60 Oe at about 350°K corresponding to ωτ(100)=1. Because of the appearance of multiple absorption modes due possibly to nonuniform Si substitution, the second predicted peak in ΔH could not be observed. Since the activation energy of both the resistivity and relaxation time constant τ(100) was 0.30 eV, it is suggested that the quasi-free valence electrons of the induced Fe2+ ions constitute the slow-relaxing system in YIG (Si0.05).

A Ferrimagnetically-Tuned Parametric Amplifier

A parametric amplifier can normally be tuned only over relatively restricted frequency ranges. One of the basic reasons for this tuning difficulty is that more than one frequency range is of importance for, in addition to the signal frequency, a pump frequency and one or more sum or difference frequencies must be considered. In this paper a tunable negative-resistance parametric amplifier is described which uses ferrimagnetically-tuned signal and idler circuits, together with a fixed-frequency pump source. This amplifier is unique in two respects. One is that the amplifier is electrically tuned through the use of yttrium iron garnet (YIG) resonators. Secondly, useful low-noise performance has been achieved over a tuning range of almost one octave, this amplifier thus successfully demonstrates that the technique of magnetic tuning with YIG resonators can be applied to a device as complex as a parametric amplifier in much the same manner as it has been applied in the past to microwave band-pass and band-stop filters.

Transverse ferroacoustic resonance

Experimental results on the transverse ferroacoustic resonance in yttrium iron garnet and in gallium substituted yttrium iron garnets are reported. A detailed comparison with theory is made. The occurrence of the resonance for different geometries is discussed and the magnitude of the resonance magnetic field is quantitatively understood. In a similar way as in ferromagnetic resonance, one can deduce the anisotropy constant from the change of the resonance field with temperature. From the line shape of the resonance, only in a few cases are we able so far to get a relaxation time out of it, mostly because of disturbing line broadening effects.

Ferro-acoustic resonance in yttrium iron garnet

Ferro-acoustic resonance in yttrium iron garnet