MAGNETIC-PROPERTIES OF HIGHLY DILUTED PDFEX AND PTFEX-ALLOYS .2. SUSCEPTIBILITY AT MICRO-KELVIN AND MILLI-KELVIN TEMPERATURES

We have measured the 16 Hz susceptibility of the giant magnetic moment s induced by Fe impurities in highly diluted PdFex and PtFex samples w ith 2.5 ppm less than or equal to x less than or equal to 75 ppm in a wide temperature range, 30 mu K less than or equal to T less than or e qual to 300 mK, and at static magnetic fields 0,01 mT less than or equ al to B less than or equal to 25 mT. We find spin glass freezing at T- f(x)/x congruent to 0,19 mK/ppm Fe for PdFex and the larger value 0.26 mK/ppm Fe for PtFex. This is the first observation of spin glass free zing in PtFex. In the low-temperature range T less than or similar to 0.5T(f)(x), the susceptibilities follow chi-chi(0) similar to T with s mall zero-temperature chi(0), values for PdFex and vanishing chi(0) va lues for PtFex. ln the paramagnetic high-temperature range, we find ch i similar to (T - theta)(-1) at T greater than or similar to 10 mK ind ependent of x for PdFex, and at T greater than or similar to 2T(f)(x) dependent of x for PtFex with vanishing theta values for both systems. The data compare well to the predictions of the Thouless-Anderson-Pal mer ''TAP'' approach of the Sherrington-Kirkpatrick ''SK'' model for s pin glasses.