Showing papers by "Hideya Onodera published in 2001"

Systematic Study on Crystal Structures in Tetragonal RB2C2 (R=Rare Earth) Compounds

Abstract: Detailed crystal structures of the tetragonal RB 2 C 2 (R=La, Ce, Pr, Nd, Tb, Dy, Ho, Er, Tm and Lu) compounds which include the antiferroquadrupolar ordering materials, DyB 2 C 2 and HoB 2 C 2 , h...

Anomalous Antiferromagnetic Properties of the Tetragonal Compound, TbB2C2

Abstract: Magnetic properties of the tetragonal compound TbB 2 C 2 were investigated by means of specific heat, magnetization and neutron diffraction measurements. TbB 2 C 2 is an antiferromagnet with T N = 21.7 K. However, the magnetic susceptibility exhibits no cusp-like anomaly but shows an increase below T N . In the ground state, the magnetic moments of Tb lie in the basal c -plane and the magnetic structure can be described with the propagation vectors of the dominant component of k =[0 1 1/2] with the weak components of k ′ =[0 0 1/2]. In addition, there also exists a weak longitudinal sinusoidal moment-modulation type component which is represented by k L =[1±δ ±δ 0], where δ=0.13. Although the fundamental magnetic correlation in RB 2 C 2 is [1 0 0]-type, the dominant component in the ground state of TbB 2 C 2 is k =[0 1 1/2]-type.

Antiferroquadrupolar Ordering in the Pseudo-Binary Tetragonal Compounds Ho1 - XDyxB2C2

Abstract: Antiferroquadrupolar (AFQ) and antiferromagnetic (AFM) transitions in Ho 1- x Dy x B 2 C 2 (0 ≤ x ≤1.0) have been investigated on the single-crystalline samples by magnetization and specific heat measurements. As the Dy concentration increases, the both transition temperatures increases from T Q =4.5 K and T N =5.9 K for x =0 to T Q =24.7 K and T N =15.3 K for x =1. For x =0.2 and 0.3, there appears a single transition at which the AFQ and AFM transitions occur simultaneously. For 0.4 ≤ x , the two transition temperatures are reversed. The temperature dependence of specific heat is interpreted well by assuming that the entropy of R ln 3 is released through the successive transitions in HoB 2 C 2 , that is, the 4 f ground state of Ho 3+ ion is a quasi-triplet. It is supposed that the Ho 3+ ion has a rather small quadrupolar moment compared with the Dy 3+ quadrupole.

Mössbauer Study on Crystallization Behavior of Glassy Fe58Co7Ni7ZrxB28-x (3 ≤x ≤18) Alloys with Variable Supercooled-Liquid Regions

Abstract: Crystallization behavior of glassy Fe58Co7Ni7ZrxB28-x (3 ≤x ≤18) alloys was examined by means of X-ray diffraction and 57Fe Mossbauer spectroscopy in order to clarify the reason for the thermal stability against crystallization, where the thermal stability correlates strongly to the width of the supercooled-liquid region. Various crystalline phases appear in the specimens quenched from and annealed at temperatures 50 K higher than the crystallization temperatures. Crystalline Fe3B and Fe2B phases characteristic of the B-rich alloys appear along with Fe2Zr and unidentified Fe–Zr–B phases characteristic of the Zr-rich alloys in the quenched Fe58Co7Ni7Zr8B20 specimen that originally has the widest supercooled-liquid region of 66 K. The competitive frustration in the forming ability of these compositional short-range order is one of the reasons for thermal stability against crystallization. Both the quenched and annealed Fe58Co7Ni7Zr3B25 specimens do not contain any phase with the Zr constituent, while the glassy Fe58Co7Ni7Zr3B25 alloy has the supercooled-liquid region of 34 K. This fact implies that the Zr impurities in Fe3B- and/or Fe2B-type compositional short-range order also play an important role in the thermal stability of these glassy alloys.