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Articles you may be interested inLarge reversible magnetocaloric effect due to a rather unstable antiferromagnetic ground state in Er 4 NiCd

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A spin glass state is observed in the double perovskite oxide Sr 2 FeCoO 6 prepared through sol-gel technique. Initial structural studies using x rays reveal that the compound crystallizes in tetragonal I4/m structure with lattice parameters, a ¼ 5.4609(2) Å and c ¼ 7.7113(7) Å . The temperature dependent powder x ray diffraction data reveal no structural phase transition in the temperature range 10-300 K. However, the unit cell volume shows an anomaly coinciding with the magnetic transition temperature thereby suggesting a close connection between lattice and magnetism. Neutron diffraction studies and subsequent bond valence sums analysis show that in Sr 2 FeCoO 6 , the B site is randomly occupied by Fe and Co in the mixed valence states of Fe 3 þ /Fe 4þ and Co 3þ /Co 4þ . The random occupancy and mixed valence sets the stage for inhomogeneous magnetic exchange interactions and in turn, for the spin glass state in this double perovskite, which is observed as an irreversibility in temperature dependent dc magnetization at T f $ 75 K. Dynamical scaling analysis of v 0 (T) yields a critical temperature T ct ¼ 75.14(8) K and an exponent z ¼ 6.2(2) typical for spin glasses. The signature of presence of mixed magnetic interactions is obtained from the thermal hysteresis in magnetization of Sr 2 FeCoO 6 . Combining the neutron and magnetization results of Sr 2 FeCoO 6 , we deduce that Fe is in low spin state while Co is in both low spin and intermediate spin states. V

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