MAGNETIC-PROPERTIES AND CRITICAL-BEHAVIOR OF GDAL2 - THERMAL-EXPANSION, MAGNETIZATION, MAGNETOSTRICTION AND MAGNETOCALORIC EFFECT

The magnetic properties of GdAl//2 have been revisited with emphasis on their critical behaviour. Thermal expansion measurement has confirmed the spontaneous volume magnetostriction to be negative ( DELTA V/V equals minus 11. 6 multiplied by 10** minus **4). The paramagnetic susceptibility has been fitted up to 2T//c by a modified Curie-Weiss law: chi equals chi //0 plus (C/T)(1 minus T//c/T)** minus ** gamma with a paramagnetic moment equal to the theoretical one for J equals 7/2 and a critical exponent gamma equals 1. 13 plus or minus 0. 01. At T equals T//c, sigma approx. H//i**1**/** delta with delta equals 3. 60 plus or minus 0. 05 and just below T//c, M//s approx. (T//c minus T)** beta with beta equals 0. 44 plus or minus 0. 015 in agreement with the scaling laws. Spontaneous and forced magnetostriction have been measured along left bracket 111 right bracket and left bracket 100 right bracket directions. lambda ** epsilon **,**2 is found to exhibit a sign opposite to the one previously given in the literature. The magnetocaloric effect has been deduced from the difference between adiabatic and isothermal strains, and derived exactly in terms of gamma above T//c.