ANALYSIS OF TBZN RESISTIVITY TEMPERATURE DERIVATIVE ABOVE THE CURIE-POINT USING SINGULAR FITTING EQUATIONS

New analyses were carried out of previously published TbZn resistivity temperature-derivative data just above the Curie temperature, T-c. Fi tting was accomplished using a weighted nonlinear least-squares progra m, GENLS, which allows one to take proper account of errors present in both the independent and the dependent variables. The utility of fitt ing with equations of either logarithmic or power-law form (involving a critical exponent lambda), both with a pole at the Curie point, was investigated in detail, Fitting results were uncertain for the four-pa rameter power-law choice but, with one parameter fixed, led to estimat es of T, of 199.61 +/- 0.02 K and of lambda of 0.16 +/- 0.01. The latt er value is rather far removed from the value of 0.104 which is expect ed for a three-dimensional (n = 1) Ising model and from the value of 0 .014 for a three-dimensional (n = 2) XY model, By contrast, fitting wi th a three-parameter logarithmic law, corresponding to a three-dimensi onal (n = 2) XY model, led to estimated standard deviations of all thr ee free parameters much smaller than the corresponding ones of the fou r-parameter power-law fit and to a T-c estimate of 199.56 +/- 0.03 K. The present results thus indicate the presence of marked XY or even Is ing anisotropy. Quadrupolar effects seem irrelevant.