•Novel self-consistent theory for the excitation and reception of magnetostatic surface spin waves.•Propagating spin wave spectroscopy employed on Ru/Co/Pt trilayer stacks and compared with a novel ...theoretical model.•Novel de-embedding procedure to isolate a pair of coplanar line antennas from nano-fabricated feeding lines.
We report on propagating spin-wave spectroscopy measurements carried out on coplanar nano-antenna devices made from a Si/SiO2/Ru(5 nm)/Co(20)/Pt(5 nm) film. The measurements were analyzed in detail by employing newly developed theoretical modeling and de-embedding procedures. The magnetic parameters of the film were determined by complementary Brillouin light scattering and ferromagnetic resonance measurements. The propagating spin wave signals could be accounted for quantitatively for the range of externally applied magnetic fields investigated in this study: 130–1500 Oe.
Interfaces of ferromagnetic transition metals such as Iron, Cobalt, and Nickel with non-magnetic palladium are of interest due to their unique magnetic and spintronic properties. These interfaces ...enable ferromagnetic resonance (FMR) based sensing of hydrogen gas. In the present work, we synthesized Fe3O4–Pd core-shell nanospheres via a one-pot synthesis method using the thermal decomposition of Fe3+ acetylacetonate in the presence of a reducing agent to produce the Fe3O4 core, followed by the reduction of a Pd2+ precursor to form the pure Pd shell. We found that our in-situ synthesized core-shell nanostructure is magnetically active and shows excellent H2 gas sensing properties. The effect of reversible hydrogen gas absorption on the magnetism of Fe3O4–Pd core-shell nanospheres was investigated. The hydrogen-induced ferromagnetic-resonance (FMR) peak shift amounted to 30% of the peak linewidth for the virgin state of the sample. In addition, in the presence of hydrogen gas, we observed a fully reversible decrease in the FMR peak linewidth by about two times. This was accompanied by a nearly doubling of the FMR peak height. Response and recovery times of about 2 and 50 s, respectively, were extracted from the measurements. All the data was collected using a mix of just 3% hydrogen in a nitrogen carrier gas.
•FeO–Pd core-shell nanospheres for the efficient detection of hydrogen gas were employed.•A one-pot synthesis method was developed to produce FeO–Pd core-shell nanospheres.•The core-shell nanosphere system showed a fast response and recovery times.•The nanospheres demonstrated superior FMR signal and reversible change upon hydrogenation.
The Fe and Co single and co-doping effects on the structural and magnetic properties of NiO nanoparticles (NPs) have been studied. The Fe and Co doping into NiO system did not induce any other ...possible secondary phase (other than NiO) and the average crystallite size was found to be in a narrow range of 33–40 nm which is suitable for studying the doping effects. Room temperature ferromagnetic resonance (FMR) measurements demonstrated the existence of a net magnetization in antiferromagnetic (AFM) NiO NPs which was observed to be increased with an increasing Fe doping and decreasing Co doping concentration. The scattered differential FMR signal for 8% Co doped NiO NPs revealed the presence of randomly oriented magnetic moments in the core of the NPs. However, decreasing the Co doping concentration and increasing the Fe doping concentration increased the degree of homogeneity of the spin structure in the system. The M − H loops taken at room temperature with S-like shape confirmed the presence of a weak ferromagnetism in the Fe doped samples in accordance with FMR analysis and attributed to the double exchange mechanism in these NPs. In ZFC/FC curves, a small peak at low temperatures, in the range of 9–18 K for all the samples, indicates the magnetization contribution from the uncompensated surface spins of these NPs. In addition, a relatively broad peak for higher Fe doping concentrations at higher temperatures indicates the onset of magnetization from the core of these NPs, where Fe and Ni ions may couple parallel or anti-parallel to each other. In summary, Co–Fe co-doping induced a core magnetization in AFM NiO NPs system and makes it attractive for various magnetic applications.
Previously, it has been shown that the strength of the perpendicular magnetic anisotropy (PMA) of thin palladium (Pd)-cobalt (Co) bilayer films can be modified when hydrogen gas is absorbed by the Pd ...layer. In our recent work, we showed that the ferromagnetic resonance (FMR) response of this material is sensitive to the changes in PMA upon exposure of Pd to hydrogen gas. As such, a simple, compact, and contactless hydrogen gas sensor could exploit the FMR-based detection of the reversible hydrogen-gas-induced changes in PMA. The magnitude of the FMR peak shift is critical to determining detection sensitivity: the higher the FMR peak shift at a given hydrogen gas concentration, the higher the sensitivity. Here, we demonstrate that the detection sensitivity is enhanced when the static magnetic field is applied perpendicular to the film plane. This is due to the frequency large shift, which is eight times larger than in the in-plane FMR configuration studied previously. An analysis based on the Kittel equation for FMR frequencies of an FM film is carried out in order to understand the mechanism of sensitivity enhancement. The result is important for optimizing Pd/Co bilayered thin films for use in novel platforms for hydrogen gas sensing.
Single crystal lithium ferrite (LiFe) spheres of sub-mm dimension are examined at mK temperatures, microwave frequencies, and variable dc magnetic field, for use in hybrid quantum systems and ...condensed matter and fundamental physics experiments. Strong coupling regimes of the photon-magnon interaction (cavity magnon polariton quasiparticles) were observed with coupling strength of up to 250 MHz at 9.5 GHz (2.6%) with magnon linewidths of order 4 MHz (with potential improvement to sub-MHz values). We show that the photon-magnon coupling can be significantly improved and exceed that of the widely used yttrium iron garnet crystal, due to the small unit cell of LiFe, allowing twice the spins per unit volume. Magnon mode softening was observed at low dc fields and, combined with the normal Zeeman effect, creates magnon spin-wave modes that are insensitive to first-order magnetic-field fluctuations. This effect is observed in the Kittel mode at 5.5 GHz (and another higher order mode at 6.5 GHz) with a dc magnetic field close to 0.19 tesla. We show that if the cavity is tuned close to this frequency, the magnon polariton particles exhibit an enhanced range of strong coupling and insensitivity to magnetic field fluctuations with both first-order and second-order insensitivity to magnetic field as a function of frequency (double magic point clock transition), which could potentially be exploited in cavity QED experiments.
We carried out numerical simulations of propagation of spin waves (magnons in quantum language) in a yttrium-iron garnet film. The numerical model is based on an original formalism. We demonstrated ...that a potential barrier for magnons, created by an Oersted field of a dc current flowing through a wire sitting on top of the film, is able to act as an electrically controlled partly transparent mirror for the magnons. We found that the mirror transparency can be set to 50% by properly adjusting the current strength, thus creating a semi-transparent mirror. A strong Hong-Ou-Mandel Effect for single magnons is expected in this configuration. The effect must be seen as two single magnons, launched simultaneously into the film from two transducers located from the opposite sides of the mirror, creating a two-microwave-photon state at the output port of one of the transducers. The probability of seeing those two-photon states at the output port of either transducer must be the same for both transducers.
Spin waves are promising candidates to carry, transport, and process information. Controlling the propagation characteristics of spin waves in magnetic materials is an essential ingredient for ...designing spin-wave-based computing architectures. Here, we study the influence of surface inhomogeneities on the spin-wave signals transmitted through thin films. We use micromagnetic simulations to study the spin-wave dynamics in an in-plane magnetized yttrium iron garnet thin film with thickness in the nanometer range in the presence of surface defects in the form of locally introduced uniaxial anisotropies. These defects are used to demonstrate that the backward volume magnetostatic spin waves (BVMSW) are more responsive to backscattering in comparison to magnetostatic surface spin waves (MSSWs). For this particular defect type, the reason for this behavior can be quantitatively related to the difference in the magnon band structures for the two types of spin waves. To demonstrate this, we develop a quasianalytical theory for the scattering process. It shows an excellent agreement with the micromagnetic simulations, sheds light on the backscattering processes, and provides a new way to analyze the spin-wave transmission rates in the presence of surface inhomogeneities in sufficiently thin films, for which the role of exchange energy in the spin wave dynamics is significant. Our study paves the way to designing magnonic logic devices for data processing which rely on a designed control of spin-wave transmission.
We fabricated microchip-sized Hydrogen (H 2 ) gas sensor based on a thin film of Iron-Palladium (FePd) alloy and investigated its ferromagnetic resonance (FMR) response in ambient and H 2 gas ...environments and at atmospheric pressure. The fabricated sensing FePd alloy layers were 30 nm thick and their composition was 52% Fe and 48% Pd. Broadband stripline FMR spectroscopy was used to study the magnetization dynamics as a function of the stripline width. A comparative study was conducted between the FMR response of the continuous film and the film of finite width. Our results suggest that a significant increase in the FMR response was recorded for the narrower width stripline (50µm) samples compared with the FMR response of continuous film samples. In addition, we observed that sample annealing in nitrogen environment enhanced the FMR response by a factor of two. Furthermore, a very strong FMR signal of 80 µV in amplitude was recorded for nitrogen-annealed samples which, according to our best knowledge, is the highest amplitude of the FMR response ever recorded for FePd films at reasonable microwave powers (10dBm). Such a significant enhancement in the FMR response is believed to be a step forward towards commercial availability of a magnetic H 2 gas sensor.
Heterostructures exhibiting perpendicular magnetic anisotropy (PMA) have traditionally served the magnetic recording industry. However, an opportunity exists to expand the applications of PMA ...heterostructures into the realm of hydrogen sensing using ferromagnetic resonance (FMR) by exploiting the hydrogen-induced modifications to PMA that occur at the interface between Pd and a ferromagnet. Here, we present the first in operando depth-resolved study of the in-plane interfacial magnetization of a Co/Pd film which features tailorable PMA in the presence of hydrogen gas. We combine polarized neutron reflectometry with in situ FMR to explore how the absorption of hydrogen at the Co/Pd interface affects the heterostructures spin-resonance condition during hydrogen cycling. Experimental data and modeling reveal that the Pd layer expands when exposed to hydrogen gas, while the in-plane magnetic moment of the Co/Pd film increases as the interfacial PMA is reduced to affect the FMR frequency. This work highlights a potential route for magnetic hydrogen gas sensing.
We have studied static and dynamic magnetic properties of a general asymmetric trilayer system using numerical simulations. For ferromagnetic, 90degrees, and antiferromagnetic coupling, the ...magnetizations of the two magnetic layers exhibit one, two, and three phases with increasing external field, respectively. The total magnetization and ferromagnetic resonance accordingly follow these phases of the magnetization vectors. The resonance condition is related to the interlayer coupling strength in such a way that a larger coupling constant yields a higher value of f sub(res)/H, where f sub(res) is the resonance frequency at the external magnetic field H. Based on the simulation results, it is proposed that measurements of the acoustic mode resonance alone at unsaturated conditions provide a sensitive and accurate technique to extract the antiferromagnetic coupling strength. The technique is demonstrated experimentally with the broadband ferromagnetic resonance measurements of two trilayer films with weak and strong coupling strengths. The technique offers an efficient and sensitive method for antiferromagnetic coupling strength extraction, yielding coupling constant values with a precision of better than 0.03 erg/cm super(2). Also, separation of the bilinear and biquadratic coupling contributions is possible with the technique.
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