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We investigated the magnetization reversal process of Ni wires fabricated on a single-crystal Y-cut 128° LiNbO 3 substrate using magnetoresistance measurement, Kerr microscopy, and micromagnetic simulation. Our study reveals the stripe-domain structure, which is originated by the competition between the shape magnetic anisotropy and additional magnetic anisotropy induced by the heterojunction, allows us to provide a pinning necessary to control the domain-wall displacement.

We report magnetic domain formation control within micro-scale polycrystalline Ni wires on a single-crystal Y-cut 128° LiNbO3 substrate. X-ray magnetic circular dichroism photoemission electron microscopy (XCDM-PEEM), micromagnetic simulations, and magnetoresistance (MR) measurements allowed us to estimate the uniaxial magnetic anisotropy induced by the magnetoelastic effect that originated at the interface between each Ni layer and the LiNbO3 substrate. Comparison of the XMCD-PEEM and MR measurement results shows that the competition between the shape magnetic anisotropy and the uniaxial magnetic anisotropy parallel to the orientation flat (OF) direction of the substrate leads to variations in both the magnetization order and the magnetization reversal process. The uniaxial magnetic anisotropy is estimated to be approximately 3.3 kJ/m3. This heterojunction structure composed of ferromagnetic and ferroelectric layers thus offers alternative ways to produce artificial functional multiferroic materials and devices.

We demonstrate the on-chip synthesis of a ruthenium complex based on a microwave-induced reaction in a microchannel coupled with a post-wall 24.15 GHz waveguide. The chip structure for continuous microwave irradiation of solvents and reactants comprises a post-wall waveguide and a microchannel that enters and exits the waveguide by passing between the metallic posts. To miniaturize the waveguide, it is designed to contain the 24.125 GHz industrial, scientific, and medical (ISM) band instead of the commonly used 2.45 GHz ISM band. Polytetrafluoroethylene (PTFE; e r = 2.1) is used as a dielectric material through which the microwaves propagate because PTFE is suitable as chemical container owing to its high resistance to heat load (up to 300 °C) and its chemical inertness. Various microfluidic configurations such as curved channels and reservoirs may be integrated into the waveguide cavity between the post walls. For a microwave input power of 3.0 W, the water temperature in the microfluidic channel increases to 75.9 °C. We used such a chip to synthesize a ruthenium complex via a microwave-induced reaction in the microchannel inside the post-wall waveguide. For this synthesis, the microwave frequency and power in the waveguide were 24.15 GHz and 3.0 W, the irradiation time was 120.0–600.0 s, and the solvent temperature was 70 °C. After microwave irradiation of the microfluidic channel, the specific fluorescence emission spectrum of Tris (2,2′-bipyridyl) ruthenium(II) is observed. This work thus demonstrates the on-chip synthesis of a ruthenium complex with a high reaction rate and yield by using a microwave-induced reaction in a microchannel inside a post-wall waveguide designed to contain 24.15 GHz microwave radiation.

We have developed a method to fabricate higher order surface enhanced Raman scattering (SERS) active structure with gold-decorated polystyrene microparticles (Au/PS microparticles) to serve a wide range of applications in life science and environmental analysis using alternating-current dielectrophoresis (DEP). It is within several tens of seconds to form or gather the SERS—active ‘hot spots’ and analyte. The immobilization of Au/PS microparticles can be demonstrated and qualitatively explained by DLVO and DEP calculation. Our method enables us to detect 4, 4′-bipyridine (4bpy) at 100 pM by an easy operation of in situ SERS platform using fiber-type simple Raman spectrometer. This platform can easily generate SERS-active ‘hot spots’ with SERS enhancement factor ∼ 10 8 in specific region on demand.

This study shows that broadband magnetic noise in a ferromagnetic wire can be detected over a wide frequency range between 500 MHz and 8 GHz using a lock-in detection technique. The magnetic noise spectrum from a 20 nm-thick single-layered Fe 19 Ni 81 wire biased with a dc current is measured as functions of an external field and dc current. This noise is caused by thermal agitation in magnetization due to ambient temperature and Joule heating. The noise behaviors are well reproduced by a stochastic model. Thus, this paper presents a stochastic analysis of magnetic noise behaviors induced by thermal agitation using a highly sensitive technique for detecting the magnetic noise in a single layered ferromagnetic wire.

We measure the broadband spectra of magnetic response in a single layered ferromagnetic nano-scale wire in order to investigate the size effect on the ferromagnetic resonance. We found that the resonance frequency difference between 300-nm- and 5-μm-wide wires was varied by about 5 GHz due to the shape anisotropy. Furthermore, we experimentally detected the magnetization precession induced by the thermal fluctuation via the rectification of a radio-frequency (rf) current by incorporating an additional direct current (dc) by using Wheatstone bridge circuit. Our investigation renders that the shape anisotropy is of great importance to control the resonance frequency and to provide thermal stability of the microwave devices.

We systematically measured the spin torque diode spectra of a magnetic tunnel junction nanoelement as a function of external magnetic field and field angle using a homemade quasi-omnidirectional broadband electrical spectrometer. The electrical spectroscopies reveal a significant higher-order spin wave modes excited in the free layer, which is substantiated by an analytical model.

The broadband ferromagnetic resonance study on both the single crystalline and polycrystalline Fe wires were performed using the rectifying effect. The effective Gilbert damping in the polycrystalline Fe wire was about three times larger than that in the single crystalline wire. This is attributed to the enhancement of the energy dissipation due to the incoherent rotation of the magnetization at the grains and grain boundaries in the polycrystalline wire. The difference between the experimental data and analytical calculation can be explained by the strong magnetic shape anisotropy that overcomes the external static magnetic field and forces the magnetization to be directed along the wire axis.

The electronic structure of monolayer hexagonal boron nitride grown on Ni by the diffusion and precipitation method was studied by x-ray absorption spectroscopy, emission spectroscopy, x-ray photoelectron spectroscopy and micro-ultraviolet photoemission spectroscopy. No indication of hybridization between h-BN pi and Ni 3d orbitals was observed. That is, the monolayer h-BN was found to be in the quasi-free-standing state. These results are in striking contrast to those of previous studies in which h-BN was strongly bound to the Ni surface by the orbital hybridization. The absence of hybridization is attributed to absence of a Ni(111) surface in this study. The lattice-matched Ni(111) surface is considered to be essential to orbital hybridization between h-BN and Ni.

The translational mode of a vortex confined in a soft magnetic Fe19Ni81 circular disk and an elliptically shaped dot causes an asymmetric response in the rectifying planar Hall voltage and dc voltage output spectra. The symmetry breaking of these spectra has been experimentally observed, and is controlled by the simultaneous application of radio-frequency current and direct current. We can qualitatively explain the asymmetry of the rectifying spectra by the nonlinear resonator model, with gyration within a large radius around the vortex equilibrium positions causing the asymmetry.

In this experiment, we investigated noise characteristics of a pulse magneto-impedance sensor which is based on an amorphous magnetic wire with a pickup coil. For a helical static magnetization, the ac current i passing the wire induces a coil voltage Vc in the coil around the wire. The pulsed excitation, combining both high and low frequency harmonic, produces the voltage Vc with dc current biasing. We describe improvements of pulse excitation conditions for an amorphous magnetic wire to reduce magnetic noises. The relation between the time interval of a current pulse train T and magnetic noises was investigated. The magnetic noise is suppressed clearly when T is smaller than 1.5 μs for pulse width 10 ns. Under the optimal conditions, the rms noise of 1-cm-long an amorphous wire magneto-impedance sensor with 600 turns of the pickup was estimated as 1pT/Hz1/2M at 20 Hz∼500 Hz.

We have investigated the dynamics of a vortex core trapped in a single layered Fe19Ni18 disk. The large amplitude excitation of the vortex core translational mode causes a shift in the resonance frequency. We can explainthe self-bistable mode where the position and amplitude of a dynamic vortex core determines the translational mode effect on the dynamic change of the gradient of the potential well. The phenomenological model that describes the self-bistability also provides an explanation for the asymmetrical spectrum shape. The self-bistability to tune the resonance using the input current would be extremely useful for high-frequency devices. This work also opens up a rich new area of study in the field of nano-scale magnets.

We developed a magnetic force microscope (MFM) where magnetic fields were applied by orthogonal electromagnets. This equipment can be used to observe magnetic domains by specifying an arbitrary angle while applying an external magnetic field of 5 kOe or less. A dot and a rectangular thin film made of permalloy were measured with this equipment. The chirality of the vortex state in the permalloy dot could be determined by using this apparatus. Furthermore, the shape of the closure domain changed every time the direction of the magnetic field was changed by 45 degrees. These results are discussed in detail together with the micromagnetics simulations.

By solving the Thiele equation with simultaneous application of a radio-frequency (rf) magnetic field $({\mathbit{h}}_{\mathrm{rf}})$ and an rf spin current $({\mathbit{j}}_{\mathrm{sp}})$, the dynamic susceptibility of exchange-coupled vortices in response to ${\mathbit{h}}_{\mathrm{rf}}$ and ${\mathbit{j}}_{\mathrm{sp}}$ was obtained. It was found that the four eigenmodes expected for two vortices trapped in a magnetic elliptical disk were coupled to different components of ${\mathbit{h}}_{\mathrm{rf}}$ and ${\mathbit{j}}_{\mathrm{sp}}$. As a consequence, orthogonal ${\mathbit{h}}_{\mathrm{rf}}$ and ${\mathbit{j}}_{\mathrm{sp}}$ (which are simultaneously generated by the application of an rf current to an elliptical disk) can excite two modes with different eigenfrequencies. This result suggests that a fieldlike nonadiabatic torque caused by an rf spin current can be spectroscopically distinguished from the one caused by the rf magnetic field.

Spin-polarized radio frequency (RF) currents and RF-Oersted fields resonantly excite a magnetic vortex core confined in a micron-scale soft magnetic disk. In this study, we measured the rectifying voltage spectra caused by the anisotropic magnetoresistance oscillation due to the gyration of the vortex with different polarity and chirality. The measured spectra are presented such that we can determine the vortex properties and strength of the spin torques and Oersted field accurately and directly through analytical calculation., Comment: 39 pages,1 table, 10 figures

We measured the specific heat, thermal expansion coefficient, magnetization, electrical resistivity, magnetoresistance and de Haas–van Alphen (dHvA) effect in PrSn 3 . The dense Kondo effect was confirmed from a negative magnetoresistance and the presence of heavy electrons with the cyclotron effective mass of 8–9 m 0 for the main Fermi surface. A magnetic anisotropy was found below T N , having an easy axis of 〈1 1 0〉.

The propagation velocities of a magnetic domain wall (DW) in polycrystalline and single-crystalline layers of $\text{Fe}(001)/\text{Au}/{\text{Fe}}_{19}{\text{Ni}}_{81}$ wires were measured using the giant magnetoresistance effect. In a single-crystalline Fe wire, the DW propagation velocity (1 km/s in a 110 Oe field at 77 K) was about three times faster than that in a polycrystalline Fe wire. This is attributable to the increase in an effective damping derived from incoherent rotation of the magnetization, which reduced the DW's mobility in the polycrystalline wire. Magnetocrystalline anisotropy plays an important role in the nucleation of DW and the switching process. Analytic solutions for the DW's motion have been found on the basis of an approximation suggested by the Slonczewski-Walker and Becker-D\"oring models; these solutions can explain our experimental results.

We have studied the Fermi surface properties in strongly anisotropic or quasi-two-dimensional systems of CePtX (X=As, P) and UX 2 (X=Sb, As). Not only the band folding but also the strong hybridization effect play an important role in the quasi-two-dimensionality for these compounds.

An anomalous Hall effect and rectification of a Hall voltage are observed by applying a radio-frequency (rf) current through a single-layered ferromagnetic wire located on a coplanar waveguide. The components of the magnetization precession, both in and perpendicular to the plane, can be detected via the Hall voltage rectification of the rf current by incorporating an additional direct current (dc). In this paper, we propose a phenomenological model, which describes the time-dependent anisotropic magnetoresistance and the time-dependent planer Hall effect. The nonlinearity of the spin dynamics accompanied by spin waves as functions of rf currents and dc is also studied, as well as those of the magnitude and orientation of the external magnetic field.

The broadband ferromagnetic resonance (FMR) measurement has been carried out by using a rectifying effect in two sets of ${\text{Ni}}_{81}{\text{Fe}}_{19}$ wires. One wire is deposited on the middle strip line of the coplanar waveguide (CPW) and another is deposited between two strip lines of the CPW, measuring the FMR induced by in-plane and out-of-plane magnetic fields, respectively. The FMR frequency is defined by detecting the magnetoresistance oscillation due to the magnetization dynamics induced by a radio frequency (rf) field. The magnetic-field dependence of the resonance frequency and the rectification spectrum are analytically interpreted based on our uniform magnetization precession model. These findings reveal that two distinct rectifying signals are anticipated by a rf field and a rf current, which can easily be controlled by engineering the ferromagnetic wire shape and the external field orientation. These fundamental understandings are crucial for future rf device applications in spintronics.

Quantum phase modulation is achieved in a metallic nanoring with a $\mathrm{FeNi}∕\mathrm{Cu}∕\mathrm{FeNi}$ (ferromagnet/normal-metal/ferromagnet) layer. Both frequency and amplitude of Aharonov-Bohm oscillation are found to be modified with respect to the magnetization configurations, indicating that the phase modulation originates from the spin-orbit scattering induced by the magnetization of the ferromagnets. Such phase modulation is ``crossover'' phenomena between mesoscopic magnetism and microscopic quantum interference effects, which provides fundamental knowledge upon quantum spin transport.

The magnetic anisotropy and the magnetization reversal process of a nanometer-scale FeNi antidot array system of triangle lattice were investigated at room temperature by means of torque and resonating-sample magnetometries. The magnetic anisotropy of the system has a sixfold rotational symmetry refracting the structural symmetry of the array of holes. The magnetic anisotropy energy between the hard and easy axes is about 3.2 × 10 4 J / m 3 .

We measured the electrical resistivity, magnetoresistance and de Haas–van Alphen effect in PrSn3. The Kondo effect was confirmed from a negative magnetoresistance and the presence of heavy electrons with the cyclotron effective mass m ∗ C =7.43–9.3 m 0 .