Masaki Kanada

Magnetic Structure of Nd2Mo2O7

Neutron diffraction studies have been carried out on a single crystal of the metallic pyrochlore ferromagnet Nd 2 Mo 2 O 7 . The magnetic structures proposed at 4 K is non-collinear for both the Mo- and Nd-moments, where the net moments of the two systems align antiparallel. In the temperature region between the Curie point (∼93 K) and ∼30 K, the moments primarily at Mo sites orders with the ferromagnetic magnetization, where the structure seems to be non-collinear, too. The ordering of the Nd moments gradually develops and becomes significant below ∼20 K with decreasing temperature. Discussion on the relationship between the magnetic structure and the anomalous transport properties is presented.

Nature of spin freezing transition of geometrically frustrated pyrochlore system R2Ru2O7 (R=rare earth elements and Y)

Abstract At the spin-glass-like transition of yttrium ruthenium pyrochlore system Y 2 Ru 2 O 7 , a significant jump of the specific heat has been found, suggesting the second order-like nature of the transition. It is commonly observed for other pyrochlore systems R 2 Ru 2 O 7 (R=various rare earth elements RE). For all REs studied here, the transition temperature T G is larger for the larger R-ions, which may be due to the increase of the transfer energies of the 4 d electrons between the neighboring Ru atoms with increasing RE ionic radius. Neutron Rietveld analyses on Y 2 Ru 2 O 7 and Nd 2 Ru 2 O 7 have revealed that below T G , the Ru spins are in an almost long-range ordered antiferromagnetic state, though it is magnetically glassy in a macroscopic sense, and that the lattice system does not participate in the transition. It is concluded that the specific heat jump is created by the purely magnetic origin.

Static Correlation and Dynamical Properties of Tb3+-moments in Tb2Ti2O7 –Neutron Scattering Study–

Static and dynamical properties of the magnetic moment system of pyrochlore compound Tb 2 Ti 2 O 7 with strong magnetic frustration, have been investigated down to the temperature T =0.4 K by neutr...

Neutron Diffraction Study of Pyrochlore Compound R2Ru2O7(R=Y,Nd) above and below the Spin Freezing Temperature.

Neutron Rietveld analyses have been carried out on Y 2 Ru 2 O 7 and Nd 2 Ru 2 O 7 to clarify the primary mechanism of the transition at T G to the spin-glass-like state which is accompanied by the specific heat jump. The results indicate that the lattice system does not seem to participate in the transition and changes of the neutron diffraction data with decreasing temperature through T G can consistently be understood by the ordering of magnetic moments at Ru sites to an almost long range ordered state, even though the low temperature phase is glassy in the macroscopic sense.

Detailed Structure of the Magnetic Excitation Spectra of YBa2Cu3Oy and Its Implication on the Physical Characteristics of the Electron System

Detailed structure of the magnetic excitation spectra χ ′′ ( q ,ω) of the superconducting oxide YBa 2 Cu 3 O 6.5 (the transition temperature \(T_{\text{c}}\cong 52\) K) in the wave vector ( q )- an...

On the Electronic and Magnetic Excitation Spectra of High-TcCu Oxides in the Normal and Superconducting States

In the discussion of the electronic excitation of high T c Cu oxides, effects of the energy broadening of the quasi particles have to be considered. If it is properly done, data of the tunneling density of states published for Bi 2 Sr 2 CaCu 2 O 8+δ system can provide a clear indication that the pseudo gap observed above T c can naturally be understood as the precursor of the superconducting gap. The broadening has been taken into account in simple calculations of the magnetic excitation spectra χ ′′ ( q , ω) of YBa 2 Cu 3 O y , with a model which is essentially based on the band picture and includes the exchange coupling among electrons. By comparing the calculated results with observed data, experimental evidence for the quasi particle broadening has been found. Brief arguments are presented if the picture of the dynamical “stripes” which affect the superconductivity works in YBa 2 Cu 3 O y .

Neutron Scattering Study of the Spin Correlation in the Spin Ice System Ho2Ti2O7

Intensity distribution of the neutron magnetic scattering has been taken in the reciprocal space of a single crystal of the “spin ice” system Ho 2 Ti 2 O 7 at the elastic energy position in the tem...

Specific heat of quasi-one-dimensional spin 1/2 system CuNb2O6

The specific heat C of CuNb 2 O 6 with quasi-one-dimensional zig-zag spin S =1/2 chains has been measured in the temperature ( T ) range between 1.6 K and 40 K. For the orthorhombic phase, a sharp anomaly of C is observed at the antiferromagnetic transition temperature T N ∼7.3 K. The T -dependence of C of the monoclinic phase, whose ground state has a spin gap, can be well described by the exchange parameters determined by fitting the magnetic susceptibility χ calculated for a model of a ferromagnetic-antiferromagnetic alternating bond to the experimentally obtained χ. The gap-value estimated from the low temperature behavior of C is about 21 K, which is also consistent with the ones obtained by other measurements. Results of the measurements of the magnetic susceptibilities χ and the specific heats C of M–Cu 1- x Zn x Nb 2 O 6 (0≤ x ≤0.5) and their structural parameters are also presented.

Neutron Inelastic Scattering Study on a Single Crystal of Tb2Ti2O7, a Magnetically Frustrated Pyrochlore System.

The dynamical magnetic behavior of pyrochlore-type Tb 2 Ti 2 O 7 with geometrically frustrated magnetic moments has been investigated by means of neutron inelastic scattering on a single crystal specimen. Dispersion curves of the magnetic excitation and the temperature ( T ) dependence of the spectral function have been studied in detail, where we have identified the pattern of the short-range magnetic correlation and the T -dependence of the correlation length.

NMR Studies on Spin-Gap Behavior of Monoclinic CuNb2O6.

The NMR Knight shift and the spin-lattice relaxation rate 1/ T 1 have been measured at Nb sites in two polymorphs of quasi one-dimensional zig-zag spin chain compounds CuNb 2 O 6 . The temperature ( T ) dependence of NMR-1/ T 1 of the monoclinic CuNb 2 O 6 indicates the existence of spin excitation gap (spin gap) whose magnitude (∼20 K) is consistent with the result of other kinds of measurements. The difference of the T -dependences between 1/ T 1 T and K is similar to that well-known for high- T c oxides. A simultaneous growing of the antiferromagnetic and the singlet correlation has been observed with decreasing T at around the temperature of the susceptibility maximum (≥20 K). Results of the NMR measurements for the orthorhombic CuNb 2 O 6 , which undergoes an antiferromagnetic transition at about 7.3 K, are also presented.