Cluster spin-glass behavior and memory effect in Cr0.5Fe0.5Ga

We report the structural, static, and dynamic properties of Cr0.5Fe0.5Ga by means of powder x-ray diffraction, dc magnetization, heat capacity, ac susceptibility, magnetic relaxation, and magnetic memory effect measurements. The dc magnetization and ac susceptibility studies reveal a spin-glass transition at around T-f similar or equal to 22 K. An intermediate value of the relative shift in freezing temperature delta T-f similar or equal to 0.017, obtained from the ac susceptibility data reflects the formation of cluster spin-glass states. The frequency dependence of T-f is also analyzed within the framework of dynamic scaling laws such as power law and Vogel-Fulcher law. The analysis using power law yields a characteristic time constant for a single spin flip tau* 1.1 x 10(-10) s and critical exponent z nu' = 4.2 +/- 0.2. On the other hand, the Vogel-Fulcher law yields the characteristic time constant for a single spin flip tau(0) similar or equal to 6.6 x 10(-9) s, Vogel-Fulcher temperature T-0 = 21.1 +/- 0.1 K, and an activation energy E-a/k(B) similar or equal to 16 K. The value of tau* and tau(0) along with a nonzero value of T-0 provide further evidence for the cluster spin-glass behavior. The magnetic field dependent T-f follows the de Almeida-Thouless (AT) line with a non-mean-field type instability, reflecting either a different universality class or strong anisotropy in the spin system. A detailed nonequilibrium dynamics study via relaxation and memory effect experiments demonstrates the evolution of the system through a number of intermediate metastable states and striking memory effects. All the above observations render a cluster spin-glass behavior in Cr0.5Fe0.5Ga, which is triggered by magnetic frustration due to competing antiferromagnetic and ferromagnetic interactions and magnetic site disorder. Moreover, the asymmetric response of magnetic relaxation with respect to the change in temperature, below the freezing temperature can be explained by the hierarchical model.