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 MnCo 2 O 4 diluted with Zn. The cationic distribution for tetrahedral A-site dilution is (Co 2þ 1ÀyA Zn 2þ yA ) A [Mn 3þ Co 3þ ] B O 4+δ , whereas B-site dilution results in (Co 2þ ) A [Mn 3þ 1ÀxB Zn 2þ xB Co 3þ ] B O 4Àδ . The strength of exchange interaction J ij 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 J ij by 17%. The frequency and temperature dependence of dynamic-susceptibility [χ ac (f , T)] studies of nanostructured compounds reveals the existence of spin-glass like behavior below the freezing temperature T F 125:7 K (for x B ¼ 0:2) and 154.3 K (y A ¼ 0:1). Relaxation time τ follows the Power-Law variation with a dynamical critical exponent zν ¼ 6:17 and microscopic spin relaxation time τ o ¼ 4:4 Â 10 À15 s for x B ¼ 0:2 (for y A ¼ 0:1, zν ¼ 5:2 and τ o ¼ 5:4 Â 10 À13 s). The amplitude and peak position in χ ac (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 T F in these Zn diluted spinels.

Reentrant canonical spin-glass dynamics and tunable field-induced transitions in (GeMn)Co2O4 Kagomé lattice

“…Consequently, the parameters obtained from the maximum value of adjusted R 2 can be considered as the optimum values for the investigated system. Utilising the parameters obtained from the Vogel-Fulcher law we have back calculated the magnitude of zν as 6.7 by means of the relationship ln 40kBT0 Ea ∼ 25 zν between Power law and Vogel-Fulcher law which matches well with the zν value obtained solely from the Power law fitting, corresponding to the canonical spin-glass systems. A systematic comparison of these magnitudes along with the values of similar type of spinel systems are listed in table 3 like as for spinglass systems e.g.…”

“…Here χ N and σ being the additional constants extracted from the equation (7) χ −1 analysis, and the difference arises due to the orbital contribution of 20 at.% of Mn 3d 3 (t 3 2g e 0 g ) spins in the Kagomé matrix. The remaining parameters for the investigated system are nearly of the same order with σ 0 and χ N being 156 Oe mol K emu −1 and 0.2123 emu mol −1 Oe −1 , respectively, while Θ = 175 K and C = 7.33 emu K mol −1 Oe −1 with the positive value of Θ representing the FiM behaviour of the system which is similar to its sister system MCO [23,25]. Nevertheless, the µ eff obtained for GMCO is significantly smaller than that of the second end compound MCO whose cationic distribution is: (Co 2+ ) A [Mn 3+ Co 3+ ] B O 4 [22].…”

“…Usually, T a represents the measure of the AFM exchange interaction which occurs between the A site Mn 4+ ions and the B site Co 2+ cations. For the case of GMCO bulk polycrystals, T a = 34.5 K, which is smaller than the magnitude of the same obtained for the end compound MCO (T a = 496.8 K) and its derivatives like Cu/Zn substituted MCO (487.9-681.1 K) [23,25]. The solid lines represent the best fits of the experimental data with equation (7).…”

“…On the other hand, the end compound MnCo 2 O 4 (MCO) shows very weak tetragonal distortion and exhibits ferrimagnetic (FiM) behaviour below ∼185 K due to the imbalance in the magnetic moments of Mn and Co ions in the spinel lattice ((Co 2+ ) A [Mn 3+ Co 3+ ] B O 4 ) [19][20][21]. With the appropriate substitution of either magnetic or non-magnetic elements at B-sites one can tune the magnetic exchange interactions (8 ⩽ J eff ⩽ 22) as well as the FiM Néel temperature (T FN ) over a wide temperature window [22][23][24][25]. Several remarkable magnetic features such as compensation phenomena, reentrant spin-glass characteristics and exchange bias has been observed in the solid-solutions of B-site diluted MCO [22,23].…”

Symbiotic, low-temperature, and scalable synthesis of bi-magnetic complex oxide nanocomposites

“…The effects of size reduction on the properties of strongly correlated electron oxides have been studied extensively over the last two decades, and are relatively well-established. [7][8][9][10][11][12][13] More importantly, this family of oxides is interesting not only from the point of fundamental studies, but also due to potential applications in different areas of technology. 14,15 In the quest for new systems with tunable properties, an alternative route that is being increasingly explored in recent years is to make nanocomposites of functional oxides, 16 where the properties of the individual components can be modied by an appropriate choice of the two phases.…”