Cationic distribution, exchange interactions, and relaxation dynamics in Zn-diluted MnCo2O4 nanostructures

Abstract

We report an experimental investigation of the electronic structure and magnetic properties of bulk and nanosized MnCo2O4 diluted with Zn. The cationic distribution for tetrahedral A-site dilution is (Co1−yA2+ZnyA2+)A[Mn3+Co3+]BO4±δ, whereas B-site dilution results in (Co2+)A[Mn1−xB3+ZnxB2+Co3+]BO4−δ. The strength of exchange interaction Jij between the magnetic ions in a bulk spinel lattice decreases by ∼15% for A-site dilution relative to the undiluted compound; however, B-site dilution results in an enhancement in Jij by 17%. The frequency and temperature dependence of dynamic-susceptibility [χac(f,T)] studies of nanostructured compounds reveals the existence of spin-glass like behavior below the freezing temperature TF∼125.7K (for xB=0.2) and 154.3 K (yA=0.1). Relaxation time τ follows the Power-Law variation with a dynamical critical exponent zν=6.17 and microscopic spin relaxation time τo=4.4×10−15s for xB=0.2 (for yA=0.1, zν=5.2 and τo=5.4×10−13s). The amplitude and peak position in χac(T) decreases with an increase in the DC bias field, which indicates that the spin-glass phase can survive in the presence of low fields forming a critical line with an exponent 2/3. This behavior is similar to the de Almeida-Thouless (AT-line) analysis in the T-H phase diagram which supports the existence of spin-glass like behavior below TF in these Zn diluted spinels.