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The isotropic transmission of magnetostatic forward volume spin waves in magnetic films with perpendicular magnetic anisotropy (PMA) is shown to be useful in the implementation of magnon-based micro-conduits. However, to our knowledge, non-magnetic-bias-field spin-wave propagation in a PMA magnetic insulator has not been achieved yet, which constrains the development of magnonic information devices and systems. Herein, we demonstrate a robust, bias-free spin-wave transmission in an 18.5- μm-thick bismuth-doped thulium iron garnet film with PMA. This ferrimagnetic film grown by liquid phase epitaxy exhibits high quality in both its crystal structure and its chemical composition and displays a large PMA field of ∼173 mT. The bias-free and reciprocal propagation of spin waves is demonstrated by all-electrical spectroscopy and provides a group velocity of 4.90 km s−1 and a decay length of 20.5 µm at zero magnetic field. Direct imaging of the remnant state indicates that the bias-free spin waves propagate along the oppositely oriented stripe domains with Bloch-type walls, which are formed by in-plane pre-magnetization. Our work contributes to the construction of isotropic charge-free micro-circuits with high levels of integration and nonvolatility.

Rare-earth iron garnet thin films with perpendicular magnetic anisotropy (PMA) have recently attracted a great deal of attention for spintronics applications. Bismuth substituted iron garnets are particularly popular among these various films because Bi3+ with a larger ion radius can adjust the lattice constant, strain state, and PMA of the films. In this paper, Tm2BiFe5O12 (TmBiIG) and Y2BiFe5O12 (YBiIG) garnet films with a series of thicknesses are prepared by radio frequency magnetron sputtering, and these films exhibit robust PMA. The microstructural properties, magnetic properties, and the anomalous Hall effect of these two kinds of films are discussed in detail. Due to their larger magnetostriction coefficient and proper tensile strain, TmBiIG films exhibit better PMA than YBiIG films, which have lower damping. As the thickness of TmBiIG and YBiIG films increases, the PMA becomes weaker, and the 40 nm YBiIG turns back to in-plane easy magnetization, but PMA is still obvious for the 64 nm TmBiIG. The ferromagnetic resonance linewidth of the 32 nm TmBiIG film is 249.08 Oe @ 13 GHz, and the damping factor is 1.49 × 10−2, which is close to that of Tm3Fe5O12. YBiIG films have better damping characteristics than TmBiIG films; however, the value is larger than that of yttrium iron garnet because of surface roughness and defects caused by larger lattice mismatch. In addition, on account of fewer defects and smaller surface roughness, the Hall voltage and Hall resistivity in TmBiIG/Pt heterostructures are larger than in YBiIG/Pt.

Ion etching is an essential step in the processing of spintronic devices. In this work, we investigated the role of argon ion (Ar+) bombardment in the spin pumping and inverse spin Hall effect in the Y3Fe5O12/Pt (YIG/Pt) heterostructure. The inverse spin Hall voltage is found to reduce by an order of two when the argon ion bombardment is employed on the YIG surface before the deposition of the Pt layer. This giant inhibition of spin injection efficiency is undesirable. In this work, we propose an experimental technique for its recovery via a chemical route. The interface property and chemical state were identified by transmission electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. We found that the argon ion bombardment on the YIG surface leads to an increase in the ratio of Fe2+ ions in the YIG/Pt interface region. Moreover, the interface magnetic moment reduces in the presence of Fe2+ ions, which resulted in the decrease in spin injection efficiency. A strong oxidizing solution (a mixture of concentrated H2SO4 and 30% H2O2 of 1:1 volume ratio) was used to recover the valence of iron and subsequently the interface magnetic moment. Our results are helpful for the understanding of the importance of interface properties and the optimization of spintronic device processing technology.

The Faraday rotation effect of both the La: yttrium iron garnet (YIG) film and the YIG metasurface were experimentally and numerically investigated in the terahertz (THz) region. A THz magneto-optic polarization measurement system was used to observe the transmission, resonance, and magneto-optical effect of the La:YIG film and YIG metasurface. The THz artificial chirality and resonance localization of the helical metasurface generate the superchiral THz field, which enhances the THz magneto-optical effect of the YIG film. The results show that the Faraday effect of the YIG metasurface is about three times that of the pure YIG film, whose differential rotation angle increases from 8° to over 24°. This work achieves more sensitively active polarization control of THz waves, which is of great significance for THz polarization conversion, sensing, and non-reciprocal transmission.

In this Letter, we investigated the influence of the fast thermal treatment on the spin pumping in ferromagnetic insulator yttrium iron garnet (YIG)/normal metal Au bilayer system. The YIG/Au bilayer thin films were treated by fast annealing process with different temperatures from 0 to 800 °C. The spin pumping was studied using ferromagnetic resonance. The surface evolution was investigated using a high resolution scanning microscopy and an atomic force microscopy. A strong thermal related spin pumping in YIG/Au bilayer system has been revealed. It was found that the spin pumping process can be enhanced by using fast thermal treatment due to the thermal modifications of the Au surface. The effective spin-mixing conductance of the fast thermal treated YIG/Au bilayer has been obtained.

In this paper, a hypothesis has been brought forward that the materials with low propagation loss in both optical and microwave band may exhibit good performance in terahertz (THz) band because THz wave band interspaces those two wave bands. Several kinds of single crystal garnet films were investigated and we found that the Lu2.1Bi0.9Fe5O12 film which grows by liquid phase epitaxy (LPE) from PbO-free flux has the best absorption properties in both microwave and optical band. In THz range, our hypothesis is well confirmed by a THz-TDS measurement which shows that the absorption coefficient of LuBiIG film is 0.05–0.3 cm−1, and the minimum value appears at 2.24 THz.

The NiZn(Ni0.4Zn0.6Fe2O4) spinel ferrite and Co2Z(Ba3Co2Fe24O41) hexagonal ferrite composite materials with the various Co2Z contents have been synthesized by the solid-state reaction method. The phases and microstructures of the sintered ceramics have been analyzed. The results show that Co2Z grains exist as a secondary phase in composites and remarkably affect the grain size and the static and high-frequency magnetic properties. With the addition ratio of Co2Z varying from 0 wt. % to 30 wt. %, the saturation magnetization only changes slightly and is closely related to the density of sintered composites. Meanwhile, the initial permeability decreases and the cut-off frequency expands from 7 MHz to 300 MHz. In addition, the product (μi − 1)fr of composites is much larger than that of the pure NiZn spinel ferrite.

A quantitative method to detect ferromagnetic resonance using magnetic tunnel junction structure has been developed. Experimental results reveal three distinct regions for single elliptical permalloy film of micrometer lateral size. Above the spin wave instability threshold, the experimental results show a linear response of the longitudinal magnetization component to the microwave field amplitude over a large range rather than a lock-up phenomenon appeared in macroscopic permalloy films and then a phase limiting behavior. The linear behavior can be described by the theoretical model describing subsidiary resonance.

We have demonstrated that spin wave resonance in a permalloy microstrip can be detected by an electrical method based on magnetic tunnel junction structures. The detection method promises high spatial resolution and sensitivity. Both even and odd spin wave resonance modes can be clearly observed in a permalloy microstrip. The spin wave induced voltage is proportional to the input microwave power at each resonance mode. Data analysis using the model of quantized dipole-exchange spin wave resonance suggests the edge pinning of spin wave sensitively depends on the order of the spin wave mode, as well as on the excitation frequency for modes of the higher order.

Yttrium iron garnet films were deposited on Si and Si/CeO2 substrates by magnetron sputtering method followed by postannealing. By varying the fabrication parameters such as sputtering atmosphere, sputtering power, and annealing atmosphere, single phase garnet films were obtained with different off-stoichiometry and film density. The dependence of cation ratio, magnetic and magneto-optical characteristics, and absorption coefficient were systemically investigated. The results reveal that a proper oxygen pressure in both sputtering and annealing process give rise to a small cation ratio of (Fe2+ or Fe4+)/Fe3+, thus is beneficial to obtain large saturation magnetization, large Faraday rotation, and small optical absorption. The sputtering power can also affect the properties of the film through changing the film density. Our results indicate that the properties of sputtering deposited yttrium iron garnet (YIG) film can be easily tuned and optimized by modifying the off-stoichiometry and density of the film,...

Ce1−xFexO2−δ polycrystalline samples with x=0%–8% were synthesized by the solid phase reaction method at a low sintering temperature of 1250 °C, and the effect of Fe content on the magnetic behaviors has been systemically investigated. It is found that the pure CeO2 samples are diamagnetic, while doped samples unambiguously show the existence of room temperature (RT) ferromagnetism (FM). With the increase in x, the saturation magnetization (Ms) exhibits a steep increase to a maximum Ms of 1 emu/g at x=2.7% and then drop exponentially. A small amount of Fe doping (0.9%) promotes the densification and induces a large dielectric constant (e). Our result shows that a relatively large e and a proper Fe concentration are critical to establish the magnetic polaron and provide strong RT FM in CeO2.

We report the design, simulation, and measurement of a dual-band metamaterial absorber in the terahertz region. Theoretical and experimental results show that the absorber has two distinct and strong absorption points near 0.45 and 0.92 THz, both which are related to the LC resonance of the metamaterial. The distributions of the power flow and the power loss indicate that the absorber is an excellent electromagnetic wave collector: the wave is first trapped and reinforced in certain specific locations and then completely consumed. This dual-band absorber has applications in many scientific and technological areas.

In this paper, the magnetic properties of these films which deposited and annealed at different atmospheres were investigated. The experimental results show that the magnetic properties of yttrium iron garnet films prepared by rf magnetron sputtering method can be tuned with oxygen partial pressure in sputtering and annealing processes. The optimal condition is depositing in atmosphere of R=0 and annealing at 0.5Pa O2, or depositing in atmosphere of R=2% and annealed in vacuum.

This paper describes the microwave properties of low temperature fired Ni0.6CuxZn(0.4−x)Fe1.96+δO4 gyromagnetic ferrite material synthesized by conventional oxide process with Bi2O3 additives. It is found that 60–63 mol % Ni and 5 mol % Cu contents have the advantage to keep the material with both low-fired characteristic and high saturated magnetization with 3 wt % Bi2O3 additives. Considering the conditions of milling, calcination, and sintering process, the low temperature fired NiCuZn gyromagnetic material was prepared with excellent microwave performances. The saturated magnetization Ms of the sample is 337 kA/m, the ferromagnetic resonance linewidth ΔH and dielectric loss tgδe less than 16 kA/m and 5.7×10−4, respectively, which has the potential applications for low temperature cofired ceramics technology to develop microwave chip circulator/isolator and passive integrated substrate.

About 3.0 μm thick SmCo-based films with additives of Fe, Cu, and Zr were deposited on Si substrates. Based on a developed semiempirical theoretical model, the dependence of the film composition on the sputtering parameters was discussed. The experimental results show that the Sm concentration increases with decreasing sputtering power or increasing Ar gas pressure, which are in good agreement with the calculated results when the preferential sputtering effect is disregarded. The effect of the sputtering parameters on the film composition provides an opportunity for the same composite target to fabricate films with Sm concentration varying from 13.8 to 17.3 at. %, which is reasonable for the permanent magnetic phase transformation (Sm2Co17→SmCo7→SmCo5). Furthermore, the observed TbCu7-type film shows a better crystal texture with a low remanence ratio for the hysteresis loops measured out plane to in plane of 0.08.

Yttrium iron garnet films were grown by radio frequency magnetron sputtering on Si(111) substrate with and without CeO2 buffer layer, and influence of CeO2 buffer on the microstructure and magnetic behaviors of the films were investigated. As compared with the film without buffer, a larger saturation magnetizaton (Ms), lower coercive force (Hc), and higher remnant magnetization (Mr) were obtained due to the introduction of CeO2 layer. The higher Ms results from the denser structure and the smaller content of Fe2+ ions. The lower Hc and higher Mr can be explained by the small surface roughness and crystal grains size. The film on CeO2 buffer layer possess fine microstructure and its surface roughness is smaller than the unbuffered films, which provides an increased exchange between the crystal grains and an enhanced spontaneous magnetization effect, leading to the higher remnant magnetization.