Extraordinary THz transmission through subwavelength semiconductor slits under antiparallel external magnetic fields

We theoretically study the resonant transmission of electromagnetic waves at the THz frequencies through subwavelength semiconductor slits under external static magnetic fields. The dispersion relations of the surface plasmon polaritons (SPPs) inside a subwavelength slit are analytically derived. It is found that the SPPs propagating along one direction and its reverse are symmetric when parallel external magnetic fields are applied, but are asymmetric when antiparallel external magnetic fields are applied. The transmission properties of periodic subwavelength semiconductor slit arrays with the antiparallel magnetic fields in each unit cell are investigated by the mode expansion technique. The two significant transmission characteristics are observed: (i) The resonant peaks are redshifted with increasing external magnetic fields; (ii) The transmissions in the two opposite directions through the slit arrays are asymmetric. The origin of the transmission asymmetry is reasonably explained by the magnetic-field induced asymmetric SPP propagation losses.     

Nonreciprocal elastic scattering of unpolarized neutrons by magnetic systems with the noncoplanar magnetization distribution

It is shown that the elastic scattering of unpolarized neutrons by systems with the noncoplanar spatial magnetic induction distribution in nonreciprocal. Two systems with the noncoplanar distribution of the magnetic field are proposed and calculated, i.e., a nanoparticle with vortex magnetization and a system of three magnetic mirrors. It is shown that, under certain conditions, the nonreciprocity is rather large and can be observed experimentally.     

Specific features of the motion of neutrons in a medium with a helical magnetic structure

The specific features of the motion of neutrons in a noncoplanar magnetic field are considered by an example of the magnetization distribution in the form of a conical helix. The reflection coefficients of neutrons from holmium crystals are calculated. It is shown that, for a noncoplanar distribution of a magnetic field in a crystal, the reflection coefficient of neutrons with spin flip exhibits an additional feature.     

Specific features of neutron propagation in a medium with a helical magnetic structure

The features of neutron motion in a noncoplanar magnetic field have been considered in the example of a specific magnetization distribution in the form of a conical helix. The neutron reflectances for holmium crystals have been calculated. It is shown that, in the case of noncoplanar distribution of magnetic field in a crystal, the spin-flip neutron reflectance has an additional singularity.     

Magnetization processes in CoNiW films

The torque curves of hard magnetic CoNiW films with perpendicular magnetic anisotropy are analysed. Using the dependence of the rotational hysteresis energy losses on the field, both in the film plane and perpendicular to it, a conclusion is drawn about the magnetic structure of the films and the mechanism of magnetization reversal consisting of an inhomogeneous rotation of the magnetization vector.     

Analysis of the magnetic domain structure of electrodeposited nickel studied by neutron depolarization

A polarized monochromatic neutron beam is transmitted through a nickel sheet which has been electrodeposited onto a copper backing. The polarization direction of the incoming beam may be adjusted in three orthogonal directions, while the polarization after transmission through the sample can be analyzed in three independent directions. In this way a (3×3) depolarization matrix can be determined, of which the diagonal elements give the depolarization factors in the successive directions. At zero applied magnetic field and perpendicular transmission no depolarization is observed when the polarization vector is perpendicular to the sheet. The depolarization factors in the other two directions nearly follow a cosine dependence on the neutron wavelength. A structure consisting of domains with magnetization directions perpendicular to the sheet could explain the results. By varying the angle of transmission of the neutron beam with respect to the plane of the sheet one can determine the mean domain size and to some extent the nature of the distribution function of the domain size in the plane of the sheet. In addition, the depolarization has been studied as a function of a magnetic field applied in a direction in the plane of the sheet. The results are compared with magnetization measurements performed in a magnetic field applied in the same direction.     

Ferromagnetic resonance features in anisotropic magnetic films with a metastable state of magnetic moment

In experiments on single-domain magnetic films with uniaxial in-plane anisotropy, a new homogeneous ferromagnetic resonance peak was observed in a planar magnetic field oriented at an angle to the easy magnetization axis and directed opposite to the magnetization projection onto the field direction. The peak was observed in fields smaller than the magnetization reversal field of the film, and the origin of the peak was found to be related to the metastable state of the magnetic moment. A good agreement was obtained between phenomenological calculations and experimental data.     

Wellenstruktur der Magnetisierung in dünnen Permalloyschichten

The magnetic ripple of thin uniaxial permalloy films is estimated by the calculus of variations. Two special cases are examined, namely average magnetization and external field in the easy and in the hard direction of the uniaxial anisotropy. When the fluctuations of the magnetization, which are connected with the fluctuations of the anisotropy, are small, the variation problem leads to differential equations which can be integrated. The solutions describe the magnetic ripple in the film. The ripple is a function of the dispersion of the anisotropy directions, the magnetic constants of the film, its thickness, and of the applied field. The agreement between theory and experiment is good.     

Critical magnetization and hysteresis of nanogranular films with perpendicular anisotropy

The magnetic-field dependences of the stability boundaries of the nonequilibrium magnetic states that exist in a nanogranular film with perpendicular anisotropy in tilted magnetic fields are theoretically described, and the corresponding critical magnetization is calculated. The field dependences of the critical magnetization of the film are analyzed at various ratios of the anisotropy field of particles to the maximum possible demagnetizing field of the film. In a tilted magnetic field, the magnetization reversal curves, which include hysteresis loops, are shown to consist of segments of the following three types: equilibrium stable magnetization, nonequilibrium stable magnetization, and critical type of magnetization.     

Chirality of a forming spin spring and remagnetization features of a bilayer ferromagnetic system

Distribution of a magnetic moment in an exchange-coupled bilayer Fe/SmCo epitaxial structure grown on a (110) MgO substrate is visualized by the magnetooptic indicator film technique. The direction and the magnitude of the effective magnetization in this structure are determined both under external magnetic fields of variable magnitude and direction and after the removal of these fields. It is shown that such a heterostructure is remagnetized by a nonuniform rotation of a magnetic moment both along the thickness of a sample and in its plane. A field antiparallel to the axis of unidirectional anisotropy gives rise to spin springs with opposite chiralities in different regions of the magnetically soft ferromagnetic layer. The contributions of these springs to the net magnetization cancel out, thus decreasing the averaged magnetic moment and the remanent magnetization without their rotation. When the external field deviates from the easy axis, the balance is violated and the sample exhibits a quasi-uniform rotation of the magnetic moment. Asymmetry in the rotation of the magnetic moment is observed under the reversal of the field as well as under repeated remagnetization cycles. It is established that a monochiral spin spring is also formed in a rotating in-plane magnetic field when the magnitude of the field exceeds the critical value. Possible mechanisms of remagnetization in this system are discussed with regard to the original disordered orientation of magnetization of the magnetically soft layer with respect to the easy axis, which is defined by the variance of unidirectional anisotropy axes of this layer on the interface.     

Balance of neutrons during their transport through magnetic noncollinear and noncoplanar layered systems

The violation of the detailed balance principle (DBP) for polarized neutrons during their mirror reflection and transport through a two-layered noncollinear magnetic structure in a magnetic field (noncoplanar system), and without it (noncollinear system), is revealed. Moreover, the existence of left-right non-polarized neutron transmission asymmetry for a noncoplanar layered system is uncovered.     

Partial magnetization reversal using laser annealing in patterned NiFe/FeMn film

We have studied local magnetization reversal by laser annealing in exchange biased NiFe/FeMn bilayer. Local magnetization reversal was performed by using the Nd:YAG laser under external magnetic field. When the laser illuminated the patterned film with the power of above 300 mW during 15 min, a magnetoresistance (MR) curve with symmetric peaks at the opposite field was obtained due to the local reversal of exchange biasing. A similar result was observed in NiFe/FeMn/NiFe trilayer. As the exposed area expanded, the intensity of opposite MR peak increased. The direction of exchange anisotropy in the partially reversed region can be restored by local laser annealing under alternating magnetic field, even if its MR peak was reduced by the damage and interdiffusion. The magnetic new domain structures of the partially reversed region was generated by laser annealing near the exposed area.     

Berry Phase of Composite System Induced by Time-Dependent Interaction

The Berry phase in a composite system induced by the time-dependent interaction is discussed. We choose two coupled spin-1/2 systems as the composite system： one of the subsystems is subjected to a static magnetic field, and the coupling parameters between two spins are controllable in time. We show that the time-dependent interaction can induce the Berry phase in a similar way as that a spin-1/2 system （qubit） is driven by an effective time-dependent magnetic field. Furthermore, using two consecutive cycles with opposite directions of both the static magnetic field as well as opposite signs of the coupling parameters, a nontrivial two-qubit unitary transformation purely based on Berry phases can be constructed.     

Dynamic magnetization reversal in dipole systems

The possibility of magnetization reversal in two different systems of magnetic dipoles by preliminary excitation of certain oscillatory regimes is demonstrated using numerical analysis of bistable states of these systems. Cyclic magnetization reversal of the systems is executed by sequential alternation of the frequency of the applied ac field. The interaction of two ring-shaped dipole systems is analyzed and peculiarities of the change in the total magnetic moments induced by this interaction are revealed.     

Finite element analysis of AC loss in non-twisted Bi-2223 tape carrying AC transport current and/or exposed to DC or AC external magnetic field

AC losses in Bi-2223 superconducting tapes carrying AC transport current and/or exposed to DC or AC magnetic field are calculated with a numerical model based on the finite element method. Superconducting property is given by the E–J characteristic represented by a power law using equivalent conductivity. First, transport loss and magnetization loss are calculated numerically and compared with measured values. The calculated losses almost agree with the measured losses. Frequency dependencies of calculated and measured transport losses are compared with each other. Next, the influence of DC external magnetic field on the transport loss is studied. DC external magnetic field reduces n that is an exponent in the power law connecting resistivity and current density. The numerically calculated transport loss increases with increasing DC magnetic field. Finally, the total loss of superconducting tape carrying AC transport current in AC magnetic field is calculated. In the perpendicular magnetic field, the calculated total loss is lager than the sum of the transport loss and the magnetization loss, while they almost agree with each other in the parallel magnetic field.     

Pinning of domain walls in two-layer ferromagnetic nanowire with scattering fields of nanoparticles

The results of a micromagnetic simulation of the pinning-depinning processes of a domain wall (DW) in a rectangular ferromagnetic nanowire (NW) consisting of two magnetic layers with scattering fields of two rectangular two-layer nanoparticles (NPs) located on NW opposite sides and oriented perpendicular to its axis are presented. The features of magnetization reversal of this system in the external magnetic field are studied depending on direction of the magnetic moments of the nanoparticle layers. The value of the depinning field in such a system depends essentially on mutual orientation of NP magnetic moments and NW magnetization. The possibility to realize a magnetic logic cell performing the “conjunction” operation of ternary logic is discussed.     

Time-odd correlation in a neutron reflectometry experiment

We find that neutron transmission of magnetic systems with the noncollinear magnetization contains a time-odd correlation. The neutron reflection from such a system violates detailed balance. Time-odd correlation is shown to violate T-invariance even in the presence of an irreversibly produced by losses and described by the imaginary part in the neutron-matter interaction.     

High field magnetization of NdAl2 single crystals interpreted with crystal field theory

The magnetization of NdAl₂ single crystals was measured at 4.2, 20.3 and 77 K, in magnetic fields up to 35 tesla applied in the 〈100〉, 〈110〉 and 〈111〉 directions. The magnetization in these directions may be described theoretically, without any fitting, in terms of two cubic crystalline electric field parameters and one molecular field constant which have been taken from inelastic neutron scattering data.⁵     

Local Observation of Field Polarity Dependent Flux Pinning by Magnetic Dipoles

A scanning Hall probe microscope is used to study flux pinning in a thin superconducting Pb film covering a square array of single-domain Co dots with in-plane magnetization. We show that single flux quanta of opposite sign thread the superconducting film below T(c) at the opposite poles of these dipoles. Depending on the polarity of the applied field, flux lines are attracted to a specific pole of the dipoles, due to the direct interaction with the vortexlike structures induced by the local stray field.     

Dynamics of magnetic charges in artificial spin ice

Artificial spin ice has been recently implemented in two-dimensional arrays of mesoscopic magnetic wires. We propose a theoretical model of magnetization dynamics in artificial spin ice under the action of an applied magnetic field. Magnetization reversal is mediated by domain walls carrying two units of magnetic charge. They are emitted by lattice junctions when the local field exceeds a critical value Hc required to pull apart magnetic charges of opposite sign. Positive feedback from Coulomb interactions between magnetic charges induces avalanches in magnetization reversal.