Electronic structure and magnetic exchange interactions in Zn diluted CuFe2O4 magneto-ceramics

Abstract

We report a detailed study on the electronic structure and temperature (1.9K≤T≤900K) dependence of magnetization in Zn diluted cuprospinel [Cu1−xZnxFe2O4 (0≤x≤0.6)]. The electronic structure determined from the x-ray photoelectron spectroscopy and Rietveld analysis of the x-ray diffraction patterns reveals the structure to be (Cu(1−x)/5ZnxFe4(1−x)/5)A [Cu4(1−x)/5Fe2−4(1−x)/5]BO4. Beyond a specific dilution limit (0.05≤xp≤0.1), a sudden phase-change from tetragonal (I41/amd) to cubic (Fd3m) is noticed with an alteration in the A–O–A (3.29%) bond angle and A–O bond length (0.67%). Our analysis shows that all these compounds order ferrimagnetically below the Néel temperature (TFN) due to dissimilar site-specific magnitudes of spins, yet, they undergo a second transition at low temperatures T1∼66K with asymptotic Curie temperature TA(=C/χ0) as high as −547.2K for the undoped case. Dilution with Zn cause quadratic decay (b2x2+b1x+yo) of the ferrimagnetic ordering temperature from 743 K to 370.5 K for x=0 and 0.6, respectively. On the contrary, a significant increase in the saturation magnetization (MS) was observed with increasing x until the critical composition xc∼0.4 beyond which MS decreases continuously (MS=1.64μB and 4.73μB for x=0 and 0.4, respectively). From the temperature dependence of inverse paramagnetic susceptibility [χ−1(T>TFN)] data and Néel’s expression for ferrimagnets, we evaluated the molecular field constants and exchange interactions (J) between the tetrahedral A- and octahedral B-sites. A systematic compositional dependence of this analysis yields that JAB (∼25kB for x=0) is the dominant exchange interaction in comparison to JBB and JAA; however, JAB decreases significantly with increasing the composition (JAB∼−5.5kB for x=0.6). The isothermal magnetization data and law of approach to saturation analysis reveals that the investigated system possesses very high anisotropy field HK ≥5.5kOe with cubic anisotropy constant K1≥1.6×106erg/cc at xc.

Spin-liquid state with precursor ferromagnetic clusters interacting antiferromagnetically in frustrated glassy tetragonal spinel Zn0.8Cu0.2FeMnO4

“…Figure 2(a) shows the core level spectrum of Zn-2p which exhibits two sharp cusps centered across 1021 eV (2p 3/2 ) and 1044 eV (2p 1/2 ) with no signatures of additional satellite peaks. The energy difference between these two cusps (∆Zn-2p (1/2−3/2) ∼ 23 eV) confirms the divalent character of Zn in ZCFMO [27,28]. Further, two humps are noticed in the core level XPS spectrum of Mn-2p (figure 2(b)) around 641.2 eV and 653.25 eV, associated with the 2p 3/2 and 2p 1/2 , respectively, confirms the trivalent electronic state of Mn [23].…”

Anisotropic Ferromagnetic Organic Nanoflowers

“…A similar trend has been noticed in case of M max ( T ) as well, except for reaching a peak at low temperatures, which shows a maximum value of 116 emu/mol at 2 K. Interestingly, the temperature variation of the differential magnetic moment, d M max /d T (shown on the right-hand-side panel), is consistent with the peak-zone of the H C ( T ). To understand the role of the magnetocrystalline anisotropy on the domain orientation of the investigated system, we employed the law of approach to saturation (LAS) technique assuming the system is having the highest symmetry. − Accordingly, the virgin magnetization isotherm obtained from the SQUID magnetometer is fitted with the mathematical expression corresponding to LAS eq (as given below).…”

Determination of the tricritical point, H–T phase diagram and exchange interactions in the antiferromagnet MnTa2O6

“…The plot indicates a clear change in the slope near 6 K marked by arrow which indicated onset of magnetic ordering from the paramagnetic (PM) to antiferromagnetic (AFM) state. However, the position of the Néel temperature T N is accurately determined by ∂(χT)/∂T vs T plots because χT represent the magnetic energy and so peaks in both ∂(χT)/∂T vs T and C P vs T plots have the same physical meaning [18,[30][31][32][33]. In AFM systems, the position of the maximum in the magnetic susceptibility (peak T P in the χ vs T plot) usually occurs above T N [33], which in this case occurs at T P ∼ 10.5 K as evident in inset of figure 7(a).…”