Magnetism and transport properties of Nd6Fe13-xAl1+x crystals

Nd6Fe13-xAl1+x (x=2.2 and 3.5) crystals were grown by the self-flux method, and their crystallographic, magnetic and electric properties were investig ated. Nd6Fe13-xAl1+x, which crystallizes in a tetragonal structure of space -group I4/mcm, shows peculiar successive magnetic transitions. In particula r, Nd6Fe9.5Al4.5 shows transitions at 20 K, 56 K and 128 K, and the spontan eous magnetization M-s at 5 K (87.5 emu/g) can be explained by assuming fer romagnetic Fe sublattices (4d up arrow 16k up arrow 16l, up arrow 16l(2)up arrow) and ferrimagnetic Nd sublattices (8f down arrow 16l up arrow). Nd6Fe 9.5Al4.5 seems to adopt ferrimagnetism in which the spontaneous magnetizati on is parallel to the [100] directions at temperatures below 20 K. A small ferromagnetic moment component, which is induced by canting of the antiferr omagnetically coupled spins along the [001] direction, exists in the [100] direction at temperatures of 20 K<T<56 K. At temperatures of 56 K<T<128 K, an antiferromagnetic spin configuration exists along the [001] direction. A first-order magnetization process was observed in the magnetization curve measured in the [001] direction in the temperature ranges 20 K<T<56 K. The electrical resistivity showed anomalies at the temperatures of each magneti c transition. Moreover, a remarkable hysteresis was observed in the field d ependence of resistivity. The magnetic phase transitions seem to have signi ficant effects on the transport properties. (C) 2000 Elsevier Science S.A. All rights reserved.