Veeturi Srinivas

Low temperature magnetic properties of binary CoxGa100-x alloy with Co concentration in the range 54 ≤ x ≤; 61.5 at% have been investigated. From the temperature and magnetic field dependent magnetization measurements magnetic phase diagram has been identified. Cluster spin glass like features are noticed in x = 54, 55 compositions, while the compositions x > 57 exhibit double magnetic transition i.e., at higher temperatures paramagnetic (PM) - ferromagnetic (FM) and at lower temperatures FM-SG like transition. The critical concentration is identified to be near x = 57 composition where discernible spontaneous magnetization emerges and the long range ferromagnetic order develops above this composition in addition to the spin glass transition (or mixed magnetic phase). Analysis of temperature dependence magnetization data in the different temperature ranges for the compositions x = 60 and 61.5 indicate that the mean field models are not suitable to understand the phase transition. Magnetic isotherms in the critical region were analyzed using non-mean-field approach and the critical exponents (γ = 1.31 and β = 0.337) found to be close to 3D Heisenberg model suggesting the importance of short range magnetic order. The data satisfies magnetic equation of state characteristic of a second order phase transition. The results obtained from the present study corroborate well with the phenomenological interacting spin cluster model.

Low temperature magnetic properties of binary CoxGa100−x (x=54–57) alloy have been investigated. Analysis of frequency dependence of ac susceptibility provided a conclusive evidence for the existence of cluster spin glass like behavior with the freezing temperature ~8, 14 K for x=54, 55.5 respectively. The parameters for conventional ‘slowing down’ of the spin dynamics have been extracted from the acs data, which confirm the presence of glassy phase. The magnitude of Mydosh parameter obtained from the fits is larger than that reported for typical canonical spin glasses and smaller than those for non-interacting ideal superparamagnetic systems but comparable to those of known cluster-glass systems. Memory phenomena using specific cooling protocols also support the spin-glass features in Co55.5Ga44.5 composition. Further the development of ferromagnetic clusters from the cluster spin glass state has been observed in x=57 composition.