Setsuo Mitsuda

Successive magnetic ordering in CuFeO2 : a new type of partially disordered phase in a triangular lattice antiferromagnet

Magnetic ordering in a rhombohedrally stacked triangular lattice antiferromagnet, CuFeO 2 was investigated on powder and single crystals by measurements of neutron diffraction, magnetic susceptibility, Mossbauer effect together with Monte Carlo simulations. CuFeO 2 was found to exhibit transitions at T N1 =16±0.5 K and T N2 =11±0.5 K. The low temperature phase has an orthorhombic magnetic unit cell with collinear moments along the c -axis, whereas the intermediate temperature phase is a partially disordered phase with a monoclinic magnetic unit cell where 1/5 of moments remain paramagnetic. The Monte Carlo simulations for the Ising spin tiangular lattice antiferromagnet can reproduce the observed successive transition in the case of the exchange parameters 4 J 3 <2 J 2 ∼ J 1 <0. This combination of exchange parameters gives an account for the stability of the collinear magnetic structure in CuFeO 2 .

Neutron Depolarization Studies on Magnetization Process Using Pulsed Polarized Neutrons

Neutron depolarization experiments investigating the magnetization processes have been performed by using pulsed polarized neutrons for the first time. Results on both quenched and annealed ferromagnets of Fe 85 Cr 15 alloy indicate the significant difference in the wavelength dependence of depolarization between them. It also constitutes the experimental demonstration of the theoretical prediction of Halpern and Holstein.

Neutron diffraction study of CuFeO2

Neutron diffraction study revealed that a powdered CuFeO 2 , a quasi-two-dimensional antiferromagnet on a triangular lattice (AFT), has two successive magnetic phase transitions at low temperatures. In the high-temperature phase below T N1 =16 K, it has a monoclinic magnetic unit cell with five spins in a layer (\(\sqrt{7}a\times\sqrt{7}a\times2{c}\), γ=141.78°). At T N2 =10 K, it shows a discontinuous transition and enters the low-temperature phase with an orthorhombic magnetic unit cell with four spins in a layer (\(\sqrt{3}a\times2{a}\times2{c}\)). In both magnetic structures, spins are collinear and parallel to the c axis.

Crystal Chirality and Helicity of the Helical Spin Density Wave in MnSi. II. Polarized Neutron Diffraction

Recent theoretical and experimental studies have shown the single handed helicity of the helical spin density wave in MnSi. In order to determine unambiguously the sense of the helicity we have carried out detailed experiments using pulsed polarized neutrons. Combining the result with that of the experiment on the crystal chirality, we have determined the left-handed or anticlockwise helicity for the left-handed chirality of the crystal symmetry. This leads to the positive sign of the antisymmetric exchange interaction in the left-handed chirality.

Reentrant Spin-Glass Transition and a Mixed Phase in an Ising System FexMn1-xTiO3

Neutron scattering demonstrates the clear reentrant spin-glass (SG) transition, for the first time, in the Ising system Fe x Mn 1- x TiO 3 for x =0.33, 0.38, 0.60, and 0.65. The samples with x =0.41, 0.50 and 0.55 exhibit paramagnetic to SG behavior upon lowering the temperature. The results confirm the SG and reentrant SG transitions which were suggested from the previous bulk susceptibility measurements by Ito et al . The reentrant SG phase is shown to be actually a mixed phase where the antiferromagnetic long range order coexists with the SG ordering. The behavior of the diffuse intensity as well as the inverse correlation length κ as a function of an Fe ion concentration x strongly suggests that there exists a phase boundary between the mixed phase and the pure SG phase. Thus the phase below the AT line in an Ising SG system should be strictly distinguished from the pure SG phase. By comparing the data of the x =0.58 sample to that of the x =0.57 sample, this phase boundary is parallel to the temperat...

An Incommensurate Magnetic Diffuse Scattering in Superconducting La1.92Sr0.08CuO4-δ

By neutron quasielastic scattering experiments, we observed a two-dimensional antiferromagnetic diffuse scattering in a superconducting La 1.92 Sr 0.08 CuO 4-δ sample at room temperature as well as in a superconducting phase. The line shape of the magnetic diffuse scattering at 295 K is a conventional Lorentzian, whereas it changes to a non-Lorentzian shape at low temperatures, presumably being a double peak structure with the peaks shifted by 0.05 a * from the antiferromagnetic zone center.

Partially disordered phase in frustrated triangular lattice antiferromagnet CuFeO2

We reinvestigated successive magnetic phase transitions ( T N1 ∼14.0 K, T N2 ∼10.5 K) in a frustrated triangular lattice antiferromagnet (TLA) CuFeO 2 by neutron diffraction measurements using single crystals. The magnetic structure of the intermediate-temperature phase between T N1 and T N2 is found to be a quasi -long range ordered sinusoidally amplitude-modulated structure with a temperature dependent propagation wave vector ( q q 0). These features of successive phase transitions are well explained by reinvestigated Monte-Carlo simulation of a 2D Ising TLA with competing exchange interactions up to 3rd neighbors, in spite of the Heisenberg spin character of orbital singlet Fe 3+ magnetic ions.

Field-Induced Magnetic Phase Transitions in a Triangular Lattice Antiferromagnet CuFeO 2 up to 14.5 T

Neutron diffraction studies on a frustrated triangular lattice antiferromagnet (TLA) CuFeO 2 have been performed under an applied magnetic field up to 14.5 T. The first-field-induced state was foun...

Electric polarization induced by a proper helical magnetic ordering in a delafossite multiferroic Cu Fe 1 − x Al x O 2

We have established the relationship between the electric polarization vector and the local spin arrangement including vector spin chirality in delafossite multiferroic

Spin Noncollinearlity in Multiferroic Phase of Triangular Lattice Antiferromagnet CuFe1-xAlxO2

\mathrm{Cu}{\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}{\mathrm{O}}_{2}