Young-Yeal Song

Growth and ferromagnetic resonance properties of nanometer-thick yttrium iron garnet films

Growth of nm-thick yttrium iron garnet films and ferromagnetic resonance (FMR) linewidth properties in the films are reported. The films were grown on gadolinium gallium garnet substrates by pulsed laser deposition (PLD). Films in the 5–35 nm thickness range showed a (111) orientation and a surface roughness between 0.1 and 0.3 nm. The 10 nm films showed a 10 GHz FMR linewidth of about 6 Oe and a damping constant of 3.2 × 10−4. The FMR linewidth increases with both the surface roughness and the surface Fe deficiency. Thicker films exhibit a smaller FMR linewidth and a lower damping constant.

Enhanced spin pumping at yttrium iron garnet/Au interfaces

Spin injection across the ferrimagnetic insulator yttrium iron garnet (YIG)/normal metal Au interface was studied using ferromagnetic resonance. The spin mixing conductance was determined by comparing the Gilbert damping parameter α in YIG/Au and YIG/Au/Fe heterostructures. The main purpose of this study was to correlate the spin pumping efficiency with chemical modifications of the YIG film surface using in situ etching and deposition techniques. By means of Ar+ ion beam etching, one is able to increase the spin mixing conductance at the YIG/Au interface by a factor of 5 compared to the untreated YIG/Au interface.

Optimized pulsed laser deposited barium ferrite thin films with narrow ferromagnetic resonance linewidths

Hexagonal M-type barium ferrite (BaM) films have been prepared by pulsed laser deposition. Optimal preparation conditions gave pure single phase films with the narrowest possible ferromagnetic resonance (FMR) linewidths. The films were deposited on c-plane sapphire substrates with a KrF excimer laser at wavelength of 248 nm and fluence of 1.7 J/cm2. The minimum linewidth films were obtained for an oxygen partial pressure of 300 mTorr and a substrate temperature of 910 °C, and were 0.85 μm thick. X-ray diffraction indicated pure single crystal BaM phase with local c-axis deviations less than 0.15°. Vibrating sample magnetometry data gave hysteresis loops with minimal hysteresis and small coercive force, saturation induction 4πMs of 4.2 kG and uniaxial anisotropy field HA of 16.4 kOe. The HA matches the anisotropy for bulk and the 4πMs is about 10% below literature values for the bulk. The FMR spectra were measured from 50 to 75 GHz by shorted wave guide techniques with the static field perpendicular to the...

In-plane c-axis oriented barium ferrite films with self-bias and low microwave loss

Hybrid pulse laser deposition and liquid phase epitaxy methods have been used to produce in-plane c-axis (IPCA) oriented barium ferrite (BaM) films on a-plane (112¯0) sapphire substrates with low microwave loss and a high remanence. Total thicknesses were from 5to20μm. A reasonable compromise for low loss and high remanence was reached at a thickness of 7μm, with a remanence ratio of 0.84 and a 59GHz peak-to-peak derivative linewidth of 250Oe. The 20μm thick film had a linewidth of 110Oe, one of the smallest values ever obtained for IPCA BaM films.

Electric field tunable 60 GHz ferromagnetic resonance response in barium ferrite-barium strontium titanate multiferroic heterostructures

A magnetic-ferroelectric film heterostructure with a large electric field tuning of the ferromagnetic resonance (FMR) mode was fabricated. Pulse laser deposited 30 nm thick Pt electrodes and 3 μm thick barium strontium titanate films on Nb-doped strontium titanate substrates were capped with an unbonded 200 μm thick single crystal in-plane c-axis barium hexaferrite slab. The structure gives a 60 GHz FMR frequency shift of 16 MHz at a bias of 29 V, for an average response of 0.55 MHz/V. The maximum incremental tuning response at 29 V was 1.3 MHz/V. This is a hundredfold improvement over previous results.

Millimeter wave notch filters based on ferromagnetic resonance in hexagonal barium ferrites

A hexagonal ferrite-based millimeter wave notch filter was demonstrated. The filter consists of an M-type BaFe12O19 (BaM) slab sitting on top of a stripline. The band-stop filtering response originates from the ferromagnetic resonance absorption in the BaM slab. The BaM slab has an in-plane uniaxial anisotropy field of 17 kOe. This anisotropy field facilitates the operation of the filter beyond 50 GHz without a need of high external fields. The operating frequency increases linearly with the external field, while the bandwidth versus field profile shows a U-shaped response. The physical mechanisms for these responses were discussed.

Electric control of magnetization relaxation in thin film magnetic insulators

Control of magnetization relaxation in magnetic insulators via interfacial spin scattering is demonstrated. The experiments use nanometer-thick yttrium iron garnet (YIG)/Pt layered structures, with the Pt layer biased by an electric voltage. The bias voltage produces a spin current across the Pt thickness. As this current scatters off the YIG surface, it exerts a torque on the YIG surface spins. This torque can reduce or enhance the damping and thereby decrease or increase the ferromagnetic resonance linewidth of the YIG film, depending on the field/current configuration.

Millimeter wave phase shifter based on ferromagnetic resonance in a hexagonal barium ferrite thin film

A hexagonal ferrite thin film-based planar millimeter-wave phase shifter was demonstrated. The device made use of an M-type barium ferrite (BaM) thin film prepared by pulsed laser deposition and a coplanar waveguide geometry. The phase tuning relied on ferromagnetic resonance in the BaM film. The device showed a phase tuning rate of 43°/(mm kOe) and an insertion loss of 3.1 dB/mm in the on-resonance regime. In off-resonance regimes, the device showed smaller loss and smaller tuning rates. The experimental results were confirmed by theoretical calculations.

Electrically and magnetically tunable phase shifters based on a barium strontium titanate-yttrium iron garnet layered structure

We report on the tuning of permittivity and permeability of a ferroelectric/ferromagnetic bilayer structure which can be used as a microwave phase shifter with two degrees of tuning freedom. The structure was prepared by the growth of a yttrium iron garnet (YIG) layer on a gadolinium gallium garnet substrate by liquid phase epitaxy, the growth of a barium strontium titanate (BST) layer on the YIG layer through pulsed laser deposition, and then the fabrication of a coplanar waveguide on the top of BST through e-beam evaporation and trilayer liftoff techniques. The phase shifters exhibit a differential phase shift of 38°/cm at 6 GHz through permittivity tuning under an applied electric field of ∼75 kV/cm and a static magnetic field of 1700 Oe. By tuning the permeability through the applied magnetic field we increase the differential phase shift to 52°/cm and simultaneously obtain a better match to the zero applied electric field condition, resulting in an improvement in the return loss from 22.4 to 24.9 dB....

Growth and ferromagnetic resonance of yttrium iron garnet thin films on metals

High-quality yttrium iron garnet (YIG) thin films were grown on a sandwich structure that consisted of a thick Cu layer and two thin cladding layers. The cladding layers were high entropy alloy nitrides (HEAN) and served as barriers to prevent Cu diffusion and oxidation during the YIG deposition. The Cu and HEAN layers were deposited by sputtering. The YIG films were grown by pulsed laser deposition. The YIG films had a thickness of several hundreds of nanometers, a surface roughness of several nanometers, and (111) orientation. The films showed a peak-to-peak ferromagnetic resonance linewidth of 1.1 Oe at 9.45 GHz.