Chin Lin

Magnetic properties of

and samples were prepared by arc melting and then annealed in vacuum. For the Nd-rich samples, type structure was obtained by a long annealing (, 48 d); for the Sm-rich samples, it was obtained by a short annealing (750 - , 1 d). With increasing Sm content, the easy magnetization direction converts from the basal plane to the c-axis. An easy-c-axis anisotropy is observed at room temperature for . A small amount of Ti favours the formation of type structure only in the Sm-rich samples. It destroys this structure in the Nd-rich samples.

Fulleride superconductors and orientational order: Tc vs lattice constant in Na2RbxCs1−xC60

Abstract The effect of orientational order on fulleride superconductivity was studied by performing DC SQUID magnetometry and high-resolution x-ray diffraction on the title quaternary phases. These are all simple cubic, Pa3space group, with the same molecular orientational order as occurs in pure C60. The Tc vs. lattice constant correlation is much steeper than is found for the merohedrally-disordered Fm3m phases, implying the possibility of large Tc enhancements with only minor additional dilation of the sc lattice. The effect of orientational order can be rationalized as primarily due to a density of states effect.

Neutron diffraction study of hard magnetic alloy MnAlC

The crystal and magnetic structure of the hard magnetic alloy Mn1.074Al0.871C0.005, which has a body centered tetragonal structure, has been investigated. Neutron diffraction data shows that Mn0.992, C0.008 occupy the (0,0,0) site and Mn0.082, Al0.871, C0.047 occupy the ( 1/2 , 1/2 , 1/2 ) site. The magnetic moments of manganese atoms are along the c axis, pointing in opposite directions for the two sites. Comparing these results with those of Mn1.09Al0.91, the significant improvement of magnetic and mechanical properties in the ternary alloy MnAlC is explained.

Neutron diffraction study of YFe10−xCoxMo2

YFe{sub 10{minus}{ital x}}Co{sub {ital x}}Mo{sub 2}(0 {le} {ital x} {le} 10) compounds were synthesized and studied by x-ray and neutron diffraction. Single phase samples with ThMn{sub 12}-type structure can be formed in the entire range of composition. Magnetic properties were studied at fields up to 70 kOe in the temperature range of 1.5 K to room temperature. X-ray diffraction analyses of aligned powders indicate that the easy magnetization direction is parallel to the {ital c} axis when {ital x}{le}6, and deviates from the {ital c} axis when {ital x}{ge}8. Neutron diffraction experiments show that the molybdenum atoms exhibit a strong preference for occupying the 8{ital i} sites, and cobalt atoms prefer to occupy the 8{ital f} and 8{ital j} sites.YFe10−xCoxMo2(0 ≤ x ≤ 10) compounds were synthesized and studied by x‐ray and neutron diffraction. Single phase samples with ThMn12‐type structure can be formed in the entire range of composition. Magnetic properties were studied at fields up to 70 kOe in the temperature range of 1.5 K to room temperature. X‐ray diffraction analyses of aligned powders indicate that the easy magnetization direction is parallel to the c axis when x≤6, and deviates from the c axis when x≥8. Neutron diffraction experiments show that the molybdenum atoms exhibit a strong preference for occupying the 8i sites, and cobalt atoms prefer to occupy the 8f and 8j sites.

Magnetic properties of Si-substituted Y2Fe17

Abstract Magnetic properties of the Si-substituted Y 2 Fe 17 have been investigated. The Curie temperature increases with increasing Si content although the unit cell volume decreases. The average Fe magnetic moment decreases with Si substitution, and the easy magnetization direction does not change. Neutron-diffraction showed that the Si atoms do not preferentially occupy the dumbbell site. The occupancy of Si atoms is very small for the 6g site, and almost statistical for the other three sites.

Permanent magnetic properties of nano-composite Sm2Fe15Si2C/α-Fe with Cu additive

The ribbons of nano-composite Sm2Fe15Si2C/α-Fe with Cu additive were prepared by melt spinning at substrate velocity v=20 m/s. The analysis of x-ray diffraction patterns shows that the relative content of α-Fe phase increases with increasing Fe percent in samples, and the average grain size of 2:17 carbides and α-Fe in the ribbons determined by the Scherrer method is about 50 and 30 nm, respectively. The ribbons exhibit a single hard magnetic phase behavior and remanence enhancement, due to inter-grain exchange coupling between hard and soft magnetic phases. The remanence increases with the increase of iron content in samples, while the coercivity decreases rapidly. The highest maximum energy product around 10.7 MGOe was obtained for Sm8Fe76Cu4Si8C4 ribbons. The reversible and irreversible magnetization portions were analyzed from the recoil loops, and an irreversible nucleation field around 4.8 kOe for hard magnetic phase was observed in Sm8Fe76Cu4Si8C4 ribbons.

Superconductivity and structural transformation in HfV2 and Nb‐doped HfV2

The temperature dependence of the specific heat shows that the strong electron‐phonon coupling system HfV2 undergoes a structural transformation at 116 K and becomes superconducting around 9 K. The structural instability can be interpreted in terms of a strong electron‐phonon coupling and Fermi surface nesting. The structural transformation shifts to lower temperatures with very dilute Nb substitution in HfV2, and completely disappears with only 5 at. % Nb. The low‐temperature specific heat of HfV2 shows a large density of states at the Fermi level. These experimental results are consistent with predictions from band‐structure calculations.

Neutron diffraction study of Nd5Fe17

Abstract Nd 5 Fe 17 is a new stable phase in the binary Nd–Fe system. X-ray diffraction of single crystals revealed a complex structure belonging to the hexagonal space group P6 3 /mcm. We perform a neutron diffraction study of Nd 5 Fe 17 powders. Position parameters, occupation of atoms, magnetic moment, coordination number, and average bond length in the hexagonal structure are reported.

From heavy fermion to mixed valence, a study of Ce(Pb1−xSnx)3

CePb3 has been shown to be a heavy‐fermion antiferromagnetic system with a Neel temperature, TN=1.1 K, and CeSn3 is a mixed valent system with considerable  f‐spd hybridization. Studies of pseudobinary alloys from CePb3 to CeSn3 provide an excellent opportunity to examine systematically the evolution of physical properties as the  f‐spd hybridization increases and the heavy‐fermion state is suppressed. Measurements of the temperature dependence of the resistivity, magnetic susceptibility, and specific heat for the pseudobinary alloy Ce(Pb1−xSnx)3 are presented and discussed. Some features obtained from this study are that, upon substitution of Sn for Pb in CePb3, the electronic specific‐heat coefficient and low‐temperature magnetic susceptibility display a monotonic variation with increasing x and TN is rapidly suppressed.

Anomalous thermodynamic, transport and Mössbauer properties of UNiSn: A half-metallic system

Abstract Of the ternary actinide compounds UTX where T is a transition metal and X is a group III, IV or V element, UNiSn is one of the more interesting, displaying anomalous behavior in the resistivity in the form of a pronounced maximum. In this paper, we present precision measurements of the electrical resistivity, low-field magnetization and specific heat which indicate that the system is paramagnetic at high temperatures and undergoes a second-order transition to a magnetically ordered state at 43 K. 119Sn Mossbauer spectroscopy shows that the hyperfine field seen at the Sn sites does not decrease to zero as T = 43 K is approached from below but continues to be detectable to temperatures approaching 55 K suggesting that the magnetic correlations persist well above the transition temperature. However, the percentage of Sn nuclei that see the hyperfine field decreases dramatically at 43 K. This data is consistent with recent neutron-scattering data that indicate that the system orders antiferromagnetically.