Search

Using soft X-ray (SX) spectromicroscopy, we show maps of the spatial distribution of constituent elements and local analysis of the density of states (DOS) related to the element-specific chemical states of diatom frustules, which are composed of naturally grown nanostructured hydrogenated amorphous silica. We applied X-ray photoemission electron microscopy (X-PEEM) as well as microprobe X-ray fluorescence (μXRF) analysis to characterize the surfaces of diatom frustules by means of X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES). We successfully demonstrated that SX spectromicroscopy is able to participate in potential observation tools as a new method to spectroscopically investigate diatom frustules.

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 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.

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.

We have found the cylindrical Fermi surfaces of CePtX (X=As, P) by the de Haas-van Alphen (dHvA) and magnetoresistance experiments. This is mainly due to the crystal structure, where the nearest neighbor distance between Pt and X atoms on the Pt-X plane is extremely short. The strong hybridization between the Pt 5 d ( x 2 - y 2 , x y ) and X p ( x , y ) states makes partially occupied anti-bonding bands, resulting in the cylindrical Fermi surfaces. The cyclotron effective mass is light, being in the range of 0.47 to 0.84 m 0 for CePtAs and 0.34 to 0.82 m 0 for CePtP. The present experimental results are well explained by the FLAPW band calculations.

We demonstrate the time-resolved real-space observation of vortex gyration in a magnetic circular disc by X-ray magnetic circular dichroism photoemission microscopy at the SPring-8 beamline BL25SU, both with and without an additional structure called a pair tag, which serves to control the magnetic curling direction. By comparing the gyration orbits of the vortices, we found that the gyration properties are dependent on the presence of the additional structure in spite of the discs having the same diameter. Furthermore, we reproduced the vortex gyration by micromagnetic simulation. The confinement potential of the vortex can be controlled by the additional structure.

We report an omnidirectional electrical spectroscopy setup for studying the spin dynamics in a nanoscale magnet. It has a measureable solid angle range comprising about 50% of the total range and allows the magnetoresistance and spin-torque diode signal to be measured simultaneously at any angle to the magnetization. This setup can provide detailed information about the spin-wave resonance modes excited in a nanoscale magnet.

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 consider the spin current induced from temperature gradient in disordered ferromagnet. Using the diagrammatic calculation, we examine a spin current in the longitudinal direction to the temperature gradient.

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.

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.

Spintronic devices, whose operation is based on the motion of a magnetic domain wall (DW), have been proposed recently. If a DW could be driven directly by flowing an electric current instead of a magnetic field, the performance and functions of such device would be drastically improved. Here we report real-space observation of the current-driven DW motion by using a well-defined single DW in a micro-fabricated magnetic wire with submicron width. Magnetic force microscopy (MFM) visualizes that a single DW introduced in the wire is displaced back and forth by positive and negative pulsed-current, respectively. We can control the DW position in the wire by tuning the intensity, the duration and the polarity of the pulsed-current. It is, thus, demonstrated that spintronic device operation by the current-driven DW motion is possible., Comment: Accepted and published in PRL

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 developed a system to carry out time-resolved photoemission electron microscopy under RF excitation at the BL25SU beamline in SPring-8. RF fields of up to ∼42 MHz could be applied to microsized magnetic disks with a power loss of less than 0.9 dB. We performed time-resolved real-space observations of the gyrotropic motion of the magnetic vortex core in Ni81Fe19 disks under an RF magnetic field. We confirmed that significant core gyrations can be seen only when the resonant frequency of the disks matches with the excitation frequency of the system.

We report the superconducting properties of LaPt 3 Si poly and single crystals with non-centrosymmetric structure. We have measured ac magnetic susceptibility, χ ac = χ' + iχ'', under sweeping magnetic fields. On the χ', a peak ascribed to the differential paramagnetic effect DPE is observed just below critical fields, where the superconducting state of LaPt 3 Si collapses completely by an external magnetic field. However this DPE behavior disappears below 0.40 K. Additionally, in this temperature range, the width of the magnetic field of collapsing superconductivity becomes broader and the superconducting domains survive even in higher magnetic fields.

The spin transport induced from an electric field in the ferromagnet with a uniform magnetization is studied microscopically. Taking into account the time dependence of the electric field and the spin relaxation due to a spin-orbit interaction at impurity, we derive the spin diffusion equation including the time evolution. We also discuss a relationship between a frequency dependence of the spin accumulation and the spin diffusion length.

A magnetic vortex core confined in a micron-scale magnetic disk is resonantly excited by both spin-polarized rf current and rf field. We found that rectifying voltage spectra caused by the resonance of vortex core are dependent not only on the core polarity, but also the chirality. These experimental results can be explained by analytically calculating the anisotropic magnetoresistance effect induced by the motion of the vortex core.

The broadband spin dynamics of patterned ferromagnetic Fe19Ni81 microwire with thickness of 80 nm has been investigated experimentally using broadband rectifying method. The rectifying effect provides a highly sensitive method to detect the high-order perpendicular standing spin wave (PSSW) mode. Present analytical calculation reproduces the observed relation between resonance frequency and applied magnetic field. The effective thickness is explained by the pinning condition of magnetic moment at the surface of the wire.

A magnetic vortex core confined in a micron-scale magnetic disk is resonantly excited by spin-polarized radio-frequency (rf) current and rf field. We show that rectifying voltage spectra caused by the vortex core resonance is dependent on the core polarity. Rectifying voltage spectra are given by the superposition of the polarity-dependent term and the polarity-independent term. The sign of the polarity-dependent rectifying voltage reverses when the sign of polarity P or external field H is reversed. This experimental result can be explained by the anisotropic magnetoresistance effect caused by the vortex core motion.

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 .

We have carried out point-contact spectroscopy measurements on CeCu6 and CeAl3 to study these heavy fermion states. Temperature and magnetic field dependences of the point-contact spectra were observed in detail. At the lowest temperature of 0.4K, differential resistance spectra of CeCu6 and CeAl3 as function of bias voltage exhibit each distinct minimum structure and additional small peak structure. Temperature evolutions of these spectra started at temperatures related to the Kondo effect, although the minimum and the peak structure emerged in reverse between both spectra of two compounds. In magnetic fields, both structures monotonically change with no distinct change without a change of curvature of magnetic field dependence of magnitude of differential resistance at zero bias voltage at critical magnetic field of meta-magnetization. This behavior in magnetic field is different from that of CeAl2, which shows antiferromagnetic ordering. This result may suggest that PCS is able to discriminate between heavy fermion state and antiferromagnetic state.