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R. K. Dokala

Publications and source records attributed to R. K. Dokala.

2 recordsLinked to original sources

Switching magnetic spin-states using small magnetic fields in compositionally complex Sm(M7)O$_3$

High-entropy perovskites (HEPs) offer a unique platform for exploring magnetic phenomena arising from extreme B-site chemical disorder. In Sm(M7)O$_3$, where there are 7 cations in equal amounts at the B-site; M = Ti, Cr, Mn, Fe, Co, Ni, Cu), we observe long-range antiferromagnetic ordering near 105 K accompanied by a small but robust excess magnetic moment intrinsic to the chemically disordered lattice. This uncompensated moment is evident from ZFC-FC irreversibility, shifts in the isothermal M(H) loops, and discrete remanent states identified through direct-current-demagnetization measurements. Remarkably, cooling fields as small as $\pm$ 20 Oe are sufficient to select the direction of the excess moment, and the chosen magnetic state remains stable against applied fields up to 50 kOe. A low-temperature anomaly in the remanent magnetization further reveals a secondary contribution from the Sm$^{3+}$ sublattice, although the primary origin of the excess moment resides in the B-site AFM sublattice.

cond-mat.mtrl-sci

Temperature Dependent Magnetic and Structural Properties of Al Substituted Nanostructured Ferrites with Large Coercive Fields

We report a comprehensive study of the temperature-dependent structural, magnetic, vibrational, and dielectric properties of Al-substituted M-type hexaferrites SrFe$_{12-x}$Al$_x$O$_{19}$. Neutron powder diffraction and Mössbauer spectrometry show that Al$^{3+}$ preferentially replaces Fe$^{3+}$ at spin-up octahedral sites (2a, 12k), disrupting the exchange coupling with the spin-down 4f tetrahedral sites and leading to a progressive reduction of site-specific magnetic moments and a systematic decrease in the Curie temperature, supported by temperature dependent susceptibility measurements. Raman spectroscopy reveals pronounced phonon anomalies near $T_C$, particularly in modes associated with bipyramidal Fe-O vibrations, reflecting the weakening of both 4e-12k and 4e-4f exchange pathways. However, the coercive field exhibits a dramatic increase, reaching $μ_0H_C$ $\sim$ 1.2 T for SrFe$_{9.6}$Al$_{2.4}$O$_{19}$, among the largest values reported for this class. Susceptibility measurements suggest that Al substitution, while weakening the superexchange network, contributes to the stabilization of single-domain behavior.

cond-mat.mtrl-sci