Yuichi Tazuke

Short Range Order Effects on EPR Frequencies in Heisenberg Linear Chain Antiferromagnets

The temperature dependence of paramagnetic resonance frequencies in a short range ordered spin state is studied theoretically and experimentally for two typical one-dimensional Heisenberg antiferromagnets, CsMnCl 3 2H 2 O and (CH 3 ) 4 NMnCl 3 . The present theory with the classical nearest-neighbor Heisenberg model properly predicts the shift of the resonant field from the high temperature limit for both crystals. The observed shift for CsMnCl 3 2H 2 O can be explained only by the dipolar term. For (CH 3 ) 4 NMnCl 3 , however, the effect of the single-ion anisotropy, or the D -term, has to be taken into account in the explanation of the temperature variation.

Magnetic properties of FexTiS2 system

Magnetization and ac-susceptibility of polycrystalline Fe x TiS 2 are measured. For x <0.38, a maximum in the ac-susceptibility is found and no spontaneous magnetization is observed. These behaviours indicate spin-glass like freezing. On the other hand, ferromagnetic properties are found for 0.38≦ x ≦0.42. The present results are discussed from the point of view that the compounds are the competing spin system having both ferromagnetic and antiferromagnetic interactions. Magnetic phase diagram is presented as a function of x .

Negative Evidences for Charge/Spin Density Wave in ZrTe5

Experimental searches were made for evidences for the charge- or spin-density wave state in the trigonal-prismatic pseudo-linear chain compound ZrTe 5 . Negative evidences for such phase transitions were provided by the absence of lattice modulation, ohmic resistivity at high electric fields, and by temperature and angular dependences of electrical resistivity and magnetic susceptibility.

EPR Line-Widths of a One-Dimensional Heisenberg Antiferromagnet CsMnCl32H2O

Temperature and angular variation of EPR line-widths of a one-dimensional Heisenberg antiferromagnet CsMnCl 3 2H 2 O have been measured at K-band frequency above its ordering temperature. A minimum in the angular variation appears at room temperature indicating the dominance of long-time, q ∼0 diffusive modes of torque correlation function. However, the line-shape is Lorentzian because of non-negligible magnitude of interchain interactions. As the temperature is lowered, they broaden and the minimum in their angular variation disappears. These phenomena can be understood when one considers the growth of intrachain spin correlation of wave vector Q 0 and the relative importance of short-time, Gaussian decay modes compared with the q ∼0 modes. Line-widths are calculated within Kubo-Tomitas framework and Fishers classical treatment. Good, quantitative agreement is attained particularly at low temperatures.

Short Range Order Effect on the Magnetic Anisotropy in a Heisenberg Linear Chain Antiferromagnet CsMnCl32H2O

Torque measurements were done for CsMnCl 3 2H 2 O in order to investigate the short range order effect on the magnetic anisotropy in a Heisenberg linear chain antiferromagnet. Above 10 K, the anisotropy in the paramagnetic susceptibility has a uniaxial symmetry referred to the direction of chains ( a -axis) corresponding to the essential intrachain spin correlations and, below this temperature, it becomes orthorhombic because of the evolution of three-dimensional magnetic correlations. The magnitude and temperature dependence of the axial anisotropy observed above 10 K could be explained by the classical linear chain model including only a small dipolar term as an anisotropy term.

Magnetic and electrical properties of the U-Si system (part II)

Abstract Compounds in the U-Si system were found to be classified into three groups; the paramagnetic heavy-fermion system (U 3 Si 5 ; γ = 120mJ/K 2 U-mol), the ferromagnet (USi; T c = 127K, μ 0 = 0.1μ B ) and Pauli paramagnetic metals (U 3 Si, U 3 Si 2 , USi 3 ).

Magnetic Susceptibility Study on RbCuCl3

Susceptibilities of single crystals of CsCuCl 3 are measured in 4.2 K< T <500 K for H ⊥ c and H // c . Behaviors characteristic to a one-dimensional Heisenberg ferromagnet with weak interchain interactions are observed. The behaviors are analyzed by the high temperature expansion approximation, and intrachain and interchain exchange interaction constants, J 0 and J 1 , are estimated. The results are, J 0 / k =(24 ±3) K and J 1 / J 0 =-0.16 ±0.04. A discontinuity in the susceptibility arising from a Jahn-Teller cooperative phase transition are observed at T t ∼420 K. The discontinuity is due to a change in J 0 at T t . Relation between the phase transition and the change of J 0 is discussed.

Electric and Magnetic Study of VxCr3-xS4 Compounds

Polycystalline samples of V x Cr 3- x S 4 (0 ≦ x ≦3) with defect nickel-arsenide structure were prepared. Almost random distribution of metal atoms was obtained by a proper treatment of the sample. Electrical resistivity was measured between 4.2 K and 295 K. It is metallic for 0.0 ≦ x ≦0.4 and 2.75 ≦ x ≦3.0, and is semiconductive for 0.6 ≦ x ≦2.5. Susceptibility was measured between 4.2 K and 800 K. Small anomalies in resistivity and susceptibility corresponding to Neel temperature were found. In mixed compounds, susceptibility deviates below the room temperature from the high temperature limit of χ=χ 0 + C /( T - θ).This behavior can be interpreted qualitatively that a small moment appears on a V atom and that this moment weakly interacts with Cr moments.

Magnetic and electrical properties of the U—Si system

Magnetic susceptibility and electrical resistivity data on polycrystal samples of U 3 Si 5 and U 3 Si 2 from 4.2 K to room temperature are presented. Both were found to be metallic paramagnets down to 4.2 K. The results suggest that both are not simple metals.

Helical Spin Resonance and Magntization Measurement in Itinerant Helimagnet FexCo1-xSi(0.3≤x≤0.85)

Measurements of electron spin resonance and magnetization have been performed on the cubic B-20 Fe x Co 1- x Si (0.3≤ x ≤0.85). The magnetization process on Fe 0.8 Co 0.2 Si indicates that this sample is a helimagnet with the cone-ferro-magnetic transition under a low magnetic field. In this sample, the helical spin resonance and the critical field resonance have been observed at 9 GHz at low temperatures, and are similar to those in MnSi observed by Date et al . The helical spin resonance data of Fe 0.8 Co 0.2 Si and MnSi are reasonably explained by the recent magnetic resonance theory for the helical spin structure due to the anti-symmetric exchange interaction existing in the cubic B-20 structure because of the lack of inversion symmetry. In every sample of Fe x Co 1- x Si, ferro- and para- magnetic resonances have been observed at 9 and 24 GHz, and are briefly discussed.