A.K. Bhatnagar

The effect of simple metal (Al, Ga) addition on the crystallisation and density of amorphous Zr-Ni alloys

Amorphous metal ribbons of (Zr0.64Ni0.36)1-xMx where M=Al, Ga and (Zr0.5Ni0.5)1-xAlx for values of x between 0 and 0.25 have been prepared by a rapid quenching technique of melt spinning. The effect of adding Al or Ga to Zr0.64Ni0.36 and Zr0.5Ni0.5 is to increase the crystallisation temperature of both host alloys. The effect of Al or Ga substitution on the thermal stability of (Zr0.64Ni0.36)1-xMx is very similar. At a composition between x=0.05 and 0.10, the M component completely suppresses the transformation to intermediate phases that has been observed in the crystallisation process for amorphous Zr-Ni alloys in a small composition range near 64 at.% Zr. The density of (Zr0.64Ni0.36)1-xAlx and of (Zr0.5Ni0.5)1-xAlx decreases linearly while that of (Zr0.64Ni0.36)1-xGax remains almost constant with x. An extension to ternary and higher order alloys of the Buschow kinetic model predicting the crystallisation temperature of binary alloys is proposed.

The Hall effect in amorphous (Zr0.64Ni0.36)1−xM x alloys (M=Al, Ga)

Values of the room temperature Hall coefficients and electrical resistivity of amorphous melt spun (Zr0.64Ni0.36)1−xAlx and (Zr0.64Ni0.36)1−xGax alloys forx=0–0.25 are reported. Addition of Al or Ga to Zr0.64Ni0.36 dramatically increases the already positive Hall coefficient of this alloy and also increases the electrical resistivity and crystallization temperature.

Low-temperature enhancement of the thermopower of amorphous (Zr0.64Ni0.36)1-xAlx alloys

Enhancements of the low-temperature thermopower of amorphous melt-quenched (Zr0.64Ni0.36)1-xAlx alloys with x=0, 0.05 , 0.10, 0.15, 0.20 and 0.25 are shown to be in good agreement with the predictions for the electron-phonon enhancement. The results imply that the low-frequency part of the Eliashberg function alpha 2( omega ) F( omega ) is proportional to omega n with n>1 for these alloys. These alloys are weak-coupling superconductors, and the addition of Al reduces the electron-phonon coupling constant lambda despite the tendency to strong coupling in simple amorphous metals.

Growth of oriented, single phase La1−xCaxMnO3 thin films by physical vapor codeposition

La1−xCaxMnO3 thin films with varying compositions (0.65>x>0.20) have been grown by codeposition of La, Ca and Mn onto single crystal LaAlO3 substrates heated to about 600°C in 10−5 Torr of oxygen. Post-deposition anneals of the films at about 900°C in pure flowing oxygen improve the magnetoresistive behavior of the films which show changes of resistance characteristic of colossal magnetoresistance between fields of 5 T and 0 with temperatures for the resistance peeks near room temperature. The annealed films have been characterized by resistance, magnetoresistance and thermopower measurements.

Superconductivity in amorphous ZrNisimple-metal ternary alloys

Abstract Values of the superconducting transition temperature T c for amorphous (Zr 0.64 Ni 0.36 ) 1− x M x and amorphous (Zr 0.5 Ni 0.5 ) 1− x M x melt-quenched alloys are reported. For the Zr-rich alloys M=Al, Ga while for the 50-50 alloy M=Al. Addition of the simple metal component rapidly depresses the transition temperature of these glassy metals.