Yasuaki Oohara

Neutron Diffraction Study on the Antiferromagnetic Insulating Ground State of β-Na0.33V2O5

The magnetic structure of the antiferromagnetically ordered state of a quasi-one-dimensional conductor β-Na 0.33 V 2 O 5 below T N =24 K was examined by neutron diffraction. The presence of magnetic Bragg reflections at ( h , k ±1/6,0), h + k =odd below T N indicates that the amplitudes of the magnetic moments at the V sites in three types of V–O chains are modulated with a period of 3 b along the chain direction (∥ b ). On the other hand, it was confirmed that the lattice modulation along the b direction occurs at ∼244 K and at ∼131 K with a period of 2 b and 6 b , respectively. Although the latter structural transition had been attributed to a “charge ordering” transition, which would result in a charge disproportionation in the V 3 d orbitals with a period of 6 b , the 3 b periodicity in the amplitude of magnetic moments strongly suggests that the charge disproportionation occurs with a period of 3 b , not 6 b . The 6 b lattice modulation developing below 131 K is therefore attributed to an instability...

ANOMALOUS FERROMAGNETIC SPIN FLUCTUATIONS IN AN ANTIFERROMAGNETIC INSULATOR PR1-XCAXMNO3

The high temperature paramagnetic state in an antiferromagnetic (AFM) insulator Pr_{1-x}Ca_{x}MnO_{3} is characterized by the ferromagnetic (FM) spin fluctuations with an anomalously small energy scale. The FM fluctuations show a precipitous decrease of the intensity at the charge ordering temperature T_{CO}, but persist below T_{CO}, and vanish at the AFM transition temperature T_{N}. These results demonstrate the importance of the spin ordering for the complete switching of the FM fluctuation in doped manganites.

Pressure effects on crystal electric field excitations in ultra-low-carrier Kondo-lattice systems CeP and CeAs

Pressure effects on crystal electric field (CEF) excitations in ultra-low carrier systems CeP and CeAs have been studied up to 2.8 GPa. There are two critical pressures P c and P B : 0.25 GPa and 1.1 GPa for CeP, while 1.3 GPa and 2.5 GPa for CeAs, respectively. CEF excitations are well-defined for P < P B , and there is no anomaly at the onset pressure of the ferromagnetic order, P c . In contrast, striking anomalies have been observed around P B . For CeP, the CEF excitation decreases to 12 meV and a new CEF excitation appears at 9 meV near P B , then it gradually replaces the first one above P B . For CeAs, a CEF excitation exhibits strong softening as well as broadening near P B . Finally, the CEF spectra exhibit strong broadening around 40 K in the low tempe rature phase near and above P B .

Electronic structures and magnetic properties in Sr1-xLaxRuO3 (0.0 ≤ x ≤ 0.5)

In order to find out more about the suppression of ferromagnetic (FM) interactions in Sr1-xLaxRuO3, electronic structures and magnetic properties have been investigated upon changing x from 0.0 to 0.5, using an XRD method with Rietveld analysis, a SQUID magnetometer and a DV-Xα computational method. In comparison with magnetic properties in Sr1-xCaxRuO3, FM interactions in Sr1-xLaxRuO3 are found to be suppressed very rapidly against x. Neither structural distortion nor cation-size disorder can account for such rapid suppression. Instead, this may be attributed to the effect of La-O hybridization created by La substitution for Sr. This hybridization effect weakens the FM order around Ru ions and, as a result, the long-range FM states are suppressed even if x is small. The DV-Xα cluster method was employed to estimate the energy difference between the up and down spin density of states in SrRuO3 and Sr0.5La0.5RuO3. This calculation predicts that Sr1-xLaxRuO3 contains La-O hybridization which suppresses FM interaction even at small x.

Neutron scattering study of magnetic successive phase transitions in RbNiCl3

Neutron scattering shows that two magnetic phase transitions occur in the triangular lattice antiferromagnet RbNiCl 3 , in which only one phase transition has been observed. Ordering of magnetic mo...

Influence of Quasi-Bi-Stripe Charge Order on Resistivity and Magnetism in the Bilayer Manganite La2-2xSr1+2xMn2O7.

The charge ordering in the bilayer manganite system La

Neutron Diffraction Study of Distorted-Triangular-Lattice Ising-like Antiferromagnet RbCoBr3

_{2-2x}

Magnetic structure of antiferromagnetic PdCrO2 Possible degenerate helices on a rhombohedral lattice

Sr

Neutron Scattering Study on Phase Transition at 74 K in Rb2ZnCl4

_{1+2x}

Neutron scattering study of magnetic ordering in CuFe0.95Al0.05O2

Mn