Jun-ichiro Kishine

Synthesis, Structure and Magnetic Properties of Chiral Molecule-Based Magnets

In this paper, we discuss the origin of magnetic chirality of chiral magnets made by chromium (III) and manganese (II) ions. Structurally characterized yellow needles: K 0.4 [Cr(CN) 6 ][Mn(S)-pn](S)-pnH 0.6 ((S)-pn = (S)-1,2-diaminopropane) and green needles: [Cr(CN) 6 ][Mn(S or R)-pnH(H 2 O)]H 2 O were obtained by the reaction among K 3 [Cr(CN) 6 ], Mn(ClO 4 ) 2 , (R or S)-pn.2HCl and KOH. The space groups of green needle and yellow needle are P2 1 2 1 2 1 and P6 1 , respectively. From the X-ray crystallographic analysis of them, the yellow needle has three-dimensional and green needle has two-dimensional magnetic connectivity. These ferrimagnets are good candidates for chiral spin order at low temperature. We present some theoretical supports, within classical phenomenologies, to understand characteristic features of the chiral magnetic materials and their magnetic properties.

Chiral Magnetic Ordering and Commensurate-to-Incommensurate Transition in CuB2O4

We measured the anisotropic magnetization processes of copper metaborate CuB 2 O 4 in detail. We propose an interpretation of the magnetization anomaly observed under the magnetic field applied perpendicular to the tetragonal axis, based on the field- and temperature-induced commensurate-to-incommensurate (C–IC) transition (Freedericksz transition) accompanied by the chiral soliton lattice formation.

Ferroelectric phase transition, ionicity condensation, and multicriticality in charge-transfer organic complexes

To elucidate a pressure-temperature phase diagram of the quasi-one-dimensional mixed-stack charge-transfer complex tetrathiafulvalene-P-chloranil (TTF-CA), we study the quasi-one-dimensional spin-1 Blume-Emery-Griffiths model. In addition to the local charge-transfer energy (Δ) and the inter-stack polar (dipole-dipole) interaction (J⊥), we take account of the interstack electrostriction (Coulomb-lattice coupling). Using the self-consistent chain-mean-field theory, where the intra-stack degrees of freedom are exactly treated by the transfer-matrix method, we reproduce the gas-liquid-solid like phase diagram corresponding to the neutral (N), paraelectric ionic (I p a r a ), and ferroelectric ionic (I f e r r o ) phases, respectively. Our classical model describes an essential point of the multicritical behavior of TTF-CA, i.e., the interchain electrostriction exclusively enhances the charge concentration (ionicity condensation), but does not affect the interchain ferroelectric coupling. This effect leads to appearance of the intermediate I p a r a phase in between the N and I f e r r o phases on the A-T phase diagram.

Transport spin current driven by the moving kink crystal in a chiral helimagnet

We show that the bulk transport magnetic current is generated by the moving magnetic kink crystal (chiral soliton lattice) formed in the chiral helimagnet under the static magnetic field applied perpendicular to the helical axis. The current is caused by the non-equilibrium transport momentum with the kink mass being determined by the spin fluctuations around the kink crystal state. An emergence of the transport magnetic currents is then a consequence of the dynamical off-diagonal long range order along the helical axis. We derive an explicit formula for the inertial mass of the kink crystal and the current in the weak field limit. PACS numbers: Valid PACS appear here How to create, transport, and manipulate spin currents is a central problem in the multidisciplinary field of spintronics. 1 The key theoretical concepts there include the current-driven spin-transfer torque 2 and resultant force acting on a domain wall (DW) 3 in metallic ferromagnetic/nonmagnetic multilayers, the dissipationless spin currents in paramagnetic spin-orbit coupled systems, 4 and magnon transport in textured magnetic structures. 5 A fundamental query behind the issue is how to describe transport magnetic currents. 6 Conventionally, the charge current is defined by the product of the carrier density and the drift velocity related via the continuity equation. In the case of spin current, the deviation of the spin projection from its equilibrium value plays a role of a charge. Then, an emergence of the transport magnetic currents may be expected in non-equilibrium state as a manifestation of the dynamical off-diagonal long range

Spin solitons in molecular magnetic materials with the chiral structure

Quasiperiodic sequences of the maxima of microwave absorption with decreasing amplitudes have been observed in a temperature range of 4–50 K in the electron spin resonance spectra of ferrimagnetic chiral single crystals [Mn{(R/S)-pn}]2[Mn{(R/S)-pn}2(H2O)][Cr(CN)6]2, as well as [Cr(CN)6][Mn(S)-pnH-(H2O)]H2O. Theoretical estimates and previous experimental data indicate that the Dzyaloshinskii-Moriya interaction is the main factor determining the chirality of the spin density and the existence of soliton solutions for the spin dynamics in these crystals. The experimental dependences obtained for the distances between the microwave power absorption maxima on the constant component of the magnetic field of the spectrometer correspond to the theoretical predictions for spin solitons in three-dimensional magnetic materials and exhibit another behavior in crystals with quasi-two-dimensional magnetic ordering.

Unconventional Magnetic Domain Structure in the Ferromagnetic Phase of MnP Single Crystals

We have studied ferromagnetic (FM) structures in the FM phase of MnP single crystals by low-temperature Lorentz transmission electron microscopy and small-angle electron diffraction analysis. In Lorentz Fresnel micrographs, striped FM domain structures were observed at an external magnetic field less than 10 Oe in specimens with the a b -plane in their plane. From real- and reciprocal-space analyses, it was clearly identified that striped FM domains oriented to the c -axis appear with Bloch-type domain walls in the b -direction and order regularly along the a -axis with a constant separation less than 100 nm. Moreover, the magnetic chirality reverses in alternate FM domain walls. These specific spin configuration of striped FM domains will affect the magnetic phase transition from the FM phase to the proper screw spiral phase at low temperature or to the FAN phase in magnetic fields in MnP.

Spin solitons and waves in chiral molecular ferrimagnets

Resonance modes corresponding to a spin-soliton resonance have been found in the electron spin resonance spectra of [Cr(CN)6][Mn(S)-pnH-(H2O)]H2O two-dimensional (2D) chiral single crystals and [Mn{(R/S)-pn}]2[Mn{(R/S)-pn}2(H2O)][Cr(CN)6]2 chiral single crystals with a 3D magnetic order. It is also established that the chiral crystals of both types exhibit a spin-wave resonance analogous to the excitation of standing spin waves in thin magnetic films. At the same time, racemic crystals of the first type do not exhibit spin-soliton resonance. The entire body of experimental data indicates that the chirality of crystals influences the spin excitations (standing spin waves and solitons) in these media.

Adiabatic and nonadiabatic spin-transfer torques in the current-driven magnetic domain wall motion

A consistent theory to describe the correlated dynamics of quantum-mechanical itinerant spins and semiclassical local magnetization is given. We consider the itinerant spins as quantum-mechanical operators, whereas local moments are considered within classical Lagrangian formalism. By appropriately treating fluctuation space spanned by basis functions, including a zero-mode wave function, we construct coupled equations of motion for the collective coordinate of the center-of-mass motion and the localized zero-mode coordinate perpendicular to the domain wall plane. By solving them, we demonstrate that the correlated dynamics is understood through a hierarchy of two time scales: Boltzmann relaxation time

Hidden Galilean symmetry, conservation laws and emergence of spin current in the soliton sector of chiral helimagnet

{\ensuremath{\tau}}_{\text{el}}

Commensurate to Incommensurate Transition in the Chiral Helimagnet CuB2O4

, when a nonadiabatic part of the spin-transfer torque appears, and Gilbert damping time