Yiyan Sun

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.

Ferromagnetic resonance of sputtered yttrium iron garnet nanometer films

Growth of nm-thick yttrium iron garnet (YIG) films by sputtering and ferromagnetic resonance (FMR) properties in the films were studied. The FMR linewidth of the YIG film decreased as the film thickness was increased from several nanometers to about 100 nm. For films with very smooth surfaces, the linewidth increased linearly with frequency. In contrast, for films with big grains on the surface, the linewidth-frequency response was strongly nonlinear. Films in the 7–26 nm thickness range showed a surface roughness between 0.1 nm and 0.4 nm, a 9.48-GHz FMR linewidth in the 6–10 Oe range, and a damping constant of about 0.001.

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.

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.

Self-biased planar millimeter wave notch filters based on magnetostatic wave excitation in barium hexagonal ferrite thin films

The use of M-type barium hexagonal ferrite (BaM) thin films for self-biased planar millimeter wave notch filters was demonstrated for the first time. The BaM film was grown by pulsed laser deposition and showed a remanent to saturation magnetization ratio of 0.99 and a 60 GHz ferromagnetic resonance linewidth of about 300 Oe. The filter consisted of a BaM film element positioned on the top of a coplanar waveguide and showed a band-stop response at 53 GHz for zero external fields. This filtering response resulted from power absorption due to magnetostatic wave excitation in the BaM film.

Yttrium Iron Garnet Nano Films: Epitaxial Growth, Spin-Pumping Efficiency, and Pt-Capping-Caused Damping

Abstract This chapter touches upon several topics related to yttrium iron garnet (YIG)-based spintronics. The chapter consists of four main sections. The first section introduces the structure and magnetic properties of YIG materials. The second section reports on the feasibility of the use of pulsed laser deposition to grow low-damping, nanometer-thick YIG films. Such films are critically needed for both fundamental studies, such as the study of spin pumping, and device applications, such as spin torque oscillators. Surface imperfection-associated damping in YIG nano films is also discussed. The third section presents the determination of efficiency of spin angular momentum transfer across YIG/normal metal interfaces. The last section reports on damping enhancement in YIG nano films due to the magnetic proximity effect in Pt capping layers. The results reported in this section not only demonstrate a new type of damping in magnetic films, but are also of practical significance, as Pt is being widely used for the generation and detection of spin currents.