Reentrant spin-glass behavior and bipolar exchange-bias effect in "Sn" substituted cobalt-orthotitanate

We report the co-existence of longitudinal ferrimagnetic behavior with Néel temperature T_N ∼ 46.1 K and reentrant transverse spin-glass state at 44.05 K in Tin (Sn) doped cobalt-orthotitanate (Co₂TiO₄). The ferrimagnetic ordering is resulting from different magnetic moments of Co²⁺ on the A-sites (3.87 μ_B) and B-sites (5.069 μ_B). The magnetic compensation temperature (T_COMP) shifts from 31.74 K to 27.1 K when 40 at. % of "Sn⁴⁺" substitutes "Ti⁴⁺" at B-sites where the bulk-magnetization of two-sublattices balance each other. For T > T_N, the dc-magnetic susceptibility (χ_dc = M/H_dc) fits well with the Néel's expression for the two-sublattice model with antiferromagnetic molecular field constants N_BB ∼ 15.44, N_AB ∼ 32.01, and N_AA ∼ 20.88. The frequency dependence of ac-magnetic susceptibility χ_ac data follows the Vogel-Fulcher law, and the power-law of critical slowing-down with "zν" = 6.01 suggests the existence of spin-clusters (where "z" and "ν" being dynamic critical-exponent and correlation length of critical-exponent, respectively). This system exhibits unusual hysteresis loops with large bipolar exchange-bias effect (H_EB ∼ 13.6 kOe at 7 K) after zero-field cooling process from an un-magnetized state, and a dramatic collapse of remanence (M_R) and coercive field (H_C) across T_COMP. The possible origins of such anomalous characteristics were discussed