SPIN GLASS - PARAMAGNETIC PHASE BOUNDARY IN AMORPHOUS MAGNETIC ALLOYS

A compositionally disordered magnetic alloy (AxB1-x)cD1-c where A and B are magnetic species while D represents the nonmagnetic atoms is considered. The competition among the exchange interactions JAA, JAB and JBB in these alloys can lead to the disappearance of the ferromagnetism (for ferromagnetic JAA) below a critical concentration x0. For x < x0, we show that while the appearance of the spin glass state at low temperatures is dependent on the relative signs of the exchange interaction, the details of the phase boundaries are controlled by the relative strength of the exchange interactions. These conclusions are borne out by our experimental results on the amorphous metal-metalloid alloys (FexNi1-x)75G25, (FexMn1-x)75G25 and (CoxMn1-x)75G25 where G25 ≡ P16B6Al3. The magnetic phase diagrams for the three alloy systems were obtained from the ac susceptibility measurements and while the slope of the spinglass paramagnetic phase boundary in the vicinity of the tricritical point is negative for the Fe-Ni alloy, it is almost zero for the Fe-Mn alloy and is positive for the Co based alloy