Fourth International Conference on Liquid and Amorphous Metals

J. Phys. Colloques 41 (1980) C8-718-C8-722
DOI: 10.1051/jphyscol:19808181

SPIN GLASS - PARAMAGNETIC PHASE BOUNDARY IN AMORPHOUS MAGNETIC ALLOYS

K. Moorjani¹, S.K. Ghatak², K.V. Rao³, B. Kramer³ et H.S. Chen<sup>4

1</sup>  Johns Hopkins University, Applied Physics Laboratory Laurel, Maryland 20910, U.S.A.
²  Physics Department, Indian Institute of Technology, Kharagpur, W. Bengal, India
³  Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, U.S.A.
⁴  Bell Laboratories, Murray Hill, New Jersey 07973, U.S.A.

Abstract
A compositionally disordered magnetic alloy (A_xB_1-x)_cD_1-c where A and B are magnetic species while D represents the nonmagnetic atoms is considered. The competition among the exchange interactions J_AA, J_AB and J_BB in these alloys can lead to the disappearance of the ferromagnetism (for ferromagnetic J_AA) 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 (Fe_xNi_1-x)₇₅G₂₅, (Fe_xMn_1-x)₇₅G₂₅ and (Co_xMn_1-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.