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X-ray powder diffraction (XRPD), magnetic susceptibility and muon-spin relaxation (μSR) measurements were carried out to investigate lattice symmetries and magnetic properties of one of alkali-meta...

We found for the first time a structural phase transition in two-dimensional kagome antiferromagnet m - N -methylpyridinium α-nitronyl nitroxide ( m -MPYNN)·BF 4 ·\(\frac{1}{3}\) (acetone). As, below T s =128.7 K, the intense satellite reflections are clearly observed at the modulation wave vector of \(q_{\text{s}}=(\frac{1}{3},\frac{1}{3},0)\), the unit cell of the low-temperature phase is enlarged to \(\sqrt{3}a\times\sqrt{3}a\times c\). In the low-temperature phase, the space group is determined to be P 31 c . The orientation of acetone molecules orders below T s , leading to the lack of the three-fold axis. To confirm whether the low-temperature phase maintains a kagome -like network structure or not, we estimate the overlap integrals between the singly occupied molecular orbital wave functions of the MPYNN molecules by the extended Huckel method. The result is that all the overlap integrals are modified below T s , suggesting that the system below T s cannot be regarded as the uniform S =1 kagome ant...

We give an overview of our studies on the electron spin resonance (ESR) in the hexagonal triangular antiferromagnets of ABX 3 type using millimeter and submillimeter waves and static and pulsed high magnetic fields. Novel ESR modes, which cannot be understood by the conventional theory of the antiferromagnetic resonance, were observed. Examples of this include that there exists the gapless excitation even for the easy-axis anisotropy. The ESR modes can be classified by the signs of the exchange interaction J 0 along the c-axis and the anisotropy. The ESR modes were calculated within the framework of the mean-field approximation using three-sublattice and six-sublattice models for the ferromagnetic and antiferromagnetic J 0 interaction, respectively. The experimental results were well described by the present calculations.

We present the ESR system with dielectric resonators for performing the high-pressure measurements. This system is constructed by combining the diamond anvil cell (or sapphire anvil cell) with the double-stacked dielectric resonators, which are commercially available. The maximum pressure is obtained to be about 15 kbar and this high-pressure ESR system holds its availability from room temperature to Liq. He temperature. This system has a potential to perform ESR measurements under high-pressure with high accuracy. As an example, we show its application to the polymerization in the TDAE–C 60 organic ferromagnet under high pressure.

Submillimeter wave ESR measurements of the ABX 3 triangular antiferromagnet CsMnBr 3 with easy-plane type anisotropy have been performed in the frequency region from 9 to 383.3 GHz. The frequency-field relations of AFMR observed below T N =8.3 K are analyzed by the molecular field theory using six sublattice model. To explain the AFMR modes, it is necessary to consider the diagonal interchain interaction J 2 as in the cases of the easy-axis type triangular antiferromagnets.

Electron Spin Resonance (ESR) measurements have been performed on axial triangular antiferromagnets CsNiBr 3 and CsMnI 3 in their lowest three-dimensional (3 D) ordered phase. The frequency vs. magnetic field diagrams are obtained in the frequency range from 9 to 380 GHz and the magnetic field up to 160 kOe. Several significant disagreements between the experimental data and the theory based on the conventional model are found. It is shown that the disagreements can be removed by the diagonal interchain exchange coupling J 2 . The ESR theory is developed taking the J 2 coupling into account. Fitting the present theory to experimental data, the interaction parameters of CsNiBr 3 and CsMnI 3 are determined.

We investigate the effects of a diagonal interchain interaction J 2 on the ESR modes in the A B X 3 -type antiferromagnets with easy-axis anisotropy.The static properties are described by replacing the conventional interchain interaction J 1 by J 1 -2 J 2 . However, because of the phase difference between the sublattice magnetizations, J 2 coupling produces marked effects on some ESR modes in cooperation with J 1 coupling. Large separation between the ω 1 -mode and EPR line for H ⊥ c and ω 2 - and ω 3 -modes for H // c ( H > H SF ) can be derived by maintaining consistency with the canting angle of spins from the c -axis and the spin wave dispersion at zero field. ESR measurements in CsMnI 3 are reported. The frequency-field diagram obtained is described well by the model involving J 2 coupling.

The temperature dependence of the Hall coefficient of CeIn3 under high pressure has been investigated. The absolute value of the Hall coefficient shows an anomalous increase below T* ∼ 80 K at ambient pressure. The increase in T* with increasing pressure is similar to the pressure dependence of the characteristic temperature where the resistivity reaches its maximum. The temperature variations below T* at various pressures are well scaled on a single curve that is the formula based on the two-fluid model. No effect of the antiferromagnetic fluctuations observed in CeTIn5 (T = Co, Rh, and Ir) is observed above 2 K even near the critical pressure where antiferromagnetic ordering disappears.

We report the change in the magnetic properties of multiferroic YbFe2O4 caused by cooling in the presence of an electrical current. The magnetization measured after the cooling is ∼10–20% smaller than that after cooling without a current. The current also affects the magnetic anisotropy below ∼100 K; the magnetic coercivity is increased by ∼10–20%. These phenomena may arise from the coexistence of ferromagnetic and antiferromagnetic domains or a disturbance in the formation of charge-ordered domains. From the viewpoint of application, the enhancement of anisotropy by an electrical current provides a method for stabilizing magnetization other than the well-known method of exchange bias.

An exchange bias (EB) behavior has been observed for multiferroic R Fe 2 O 4 ( R =Y, Er, Tm, Yb, Lu, and In). The materials with small R 3+ ions ( R =Tm, Yb, Lu, and In) exhibit large EB fields (\({\gtrsim}1\) kOe) below ∼100–150 K. This property is rooted in a magnetically glassy state, arising from the competition between ferromagnetic and antiferromagnetic domain interactions. In addition, the EB field tends to be more enhanced for smaller R 3+ ions. Hence, the EB is controlled by the substitution at the R -site in this series.

We have studied the ground state of an organic quasi-one-dimensional (Q1D) ferromagnet, the γ-phase para -nitrophenyl nitronyl nitroxide (γ- p -NPNN), by low-frequency ESR and magnetic torque measu...