Temperature Versus Composition Phase Diagrams and Spin Glass Behavior in Low Dimensional, Mixed Magnetic Systems.

The temperature versus composition phase diagrams for several low dimensional, mixed magnetic systems have been investigated. The magnetic behavior of the pseudo -one-dimensional mixed systems ((CH_3)_3 NH) A_{rm (1-x)} B_{rm x}Cl _{3} cdot 2H _2O where A and B are Co, Ni, and Mn, was investigated as a function of x. The mixture with Co and Ni was found to exhibit spin glass behavior below a characteristic temperature T_{rm g} as evidenced by the onset of time dependent thermoremanent magnetization. The phase diagram of temperature versus x showed a very broad and deep spin glass region with unusually thin antiferromagnetic phase regions above it. A tetracritical point near x = 0.58 was indicated. Thermoremanent magnetization versus time below T_{ rm g} was fit to a stretched exponential function plus a constant offset term. Mixtures of Mn with Co and Mn with Ni showed no spin glass behavior above 2 K and had a deep depression in the center of their temperature versus x phase diagrams. The pseudo-two-dimensional mixed systems, (NH_3(CH_2) _{rm n}NH_3 ) CuCl_{rm 4x}Br _{rm 4(1-x)} for n = 5 and 7 were also investigated. The temperature versus x phase diagrams for these systems also showed evidence of tetracritical points but with mixed phase regions rather than spin glass phases. From an examination of the differences in these systems, criteria for development of mixed phases and spin glass phases were discussed.