Interplay of lattice-spin-orbital coupling and Jahn-Teller effect in -noncollinear spinel Ti_xMn_1-x(FeyCo_1-y)₂O₄: A neutron diffraction study

Abstract Local magnetostructural changes and dynamical spin fluctuations in doubly diluted spinel Mn1-xTix(Co1-yFey)2O4 has been reported by means of neutron diffraction and magnetization studies. Two distinct set of compositions (i) x = 0.8 and y = 0.18 and (ii) x = 0.6 and y = 0.435 have been considered for the analysis. The first set of equivalent stoichiometry (Mn0.80Ti0.20Fe0.36Co1.64O4) exhibits enhanced tetragonal distortion across the ferrimagnetic Néel temperatures (TFN as high as 298 K) in comparison to the end compound MnCo2O4 (TFN ~180 K) with a characteristic ratio ct/√t of 0.99795(8). However, in the second case with higher B-site compositions, the presence of Jahn-Teller ions with distinct behavior appears to counterbalance the strong tetragonal distortion. Both the investigated systems show the coexistence of noncollinear antiferromagnetic and ferrimagnetic components in cubic and tetragonal settings. On the other hand, the dynamical ac-susceptibility, χac(T) reveals a cluster spin-glass state with Gaby-Toulouse (GT) like mixed phases behavior below TFN. Such dispersive behavior appears to be sensitive to the level of octahedral substitution. Further, the field dependence of χac (T) follows the weak anisotropic GT-line behavior with crossover exponent Φ lies in the range 1.38 - 1.52 on the H-T plane which is in contrast to the B-site Ti substituted MnCo2O4 spinel that appears to follow irreversible non-mean-field AT-line behavior (Φ ~ 3 + δ). Finally, the Arrott plots analysis indicates the presence of a pseudo first-order like transition (T < 20 K) which is in consonance with and zero crossover of the magnetic entropy change within the frozen spin-glass regime.