Structural, Magnetic, Electrical, and Magnetoelectric Properties of Sm- and Ho-Substituted Nickel Ferrites

Abstract

Sm-and Ho-substituted and pure nickel ferrite materials, namely, NiFe 1.925 Sm 0.075 O 4 , NiFe 1.925 Ho 0.075 O 4 , and NiFe 2 O 4 , have been synthesized by the solid-state chemical reaction, and their structural, magnetic, dc electrical conductivity, ferromagnetic, ferroelectric, and dielectric properties have been evaluated. Sm-and Ho-substituted nickel ferrites crystallize in the cubic inverse spinel phase with a very small amount of SmFeO 3 and HoFeO 3 as the additional phase, respectively. X-ray diffraction studies indicate rhombohedral distortion in NiFe 1.925 Sm 0.075 O 4 and NiFe 1.925 Ho 0.075 O 4 compounds. The existence of ferroelectricity in NiFe 1.925 Sm 0.075 O 4 and NiFe 1.925 Ho 0.075 O 4 has been confirmed from the ferroelectric loops, and the respective transition temperatures are 543 and 677 K. The respective magnetocapacitance values are -1.8% and -1.2%. Magnetoelectric coefficients observed at 500 Oe in the NiFe 1.925 Sm 0.075 O 4 and NiFe 1.925 Ho 0.075 O 4 compounds are 1.82 and 1.84 mV cm -1 Oe -1 , respectively. A considerable increase in the saturation magnetostriction value has been observed upon the substitution of Sm. Substitution of Sm and Ho for Fe at the B site increases the dielectric constant compared to that of pure nickel ferrite. Frequency variation of the dielectric constant shows a dispersion that can be modeled with a modified Debye function, which considers the possibility of more than one ion contributing to the relaxation. Electrical conductivity curves confirm the improved resistivity of the NiFe 1.925 Sm 0.075 O 4 and NiFe 1.925 Ho 0.075 O 4 compounds compared to that of pure nickel ferrite. Analysis of the temperature-dependent conductivity indicates that the small polaron and variable-range-hopping mechanisms are operative in the 220-300 and 160-220 K temperature regions, respectively.

Effect of frustrated exchange interactions and spin-half-impurity on the electronic structure of strongly correlated NiFe2O4

“…phase fractions of different phases present in the compound) of inverse spinel phase and the secondary phase respectively are found to be 0.95 and 0.05 for x = 0.05 and 0.91 and 0.09 for x = 0.075. Table I shows that, in agreement with earlier reports [7][8][9][10], an increment in the lattice constant was observed for the doped compounds which is attributed to the larger ionic radius of Yb 3+ (0.86Å) compared to that of Fe…”

“…In the present study, the electronic structure of NFO is revisited in order to examine the effect of substitution of Yb as well as to explain the insulating mechanism of the parent compound. Table III), which is in agreement with those reported in literature [7,8,12,14,35]. In order to examine the role of strong correlation effect on the insulating behavior, the partial densities of states obtained using GGA and GGA+U are shown in Fig.…”

“…A decrease in T C upon the partial substitution of R 3+ for Fe 3+ in NFO has been reported from our lab [7,8]. In Ni 2 Fe 1.925 R 0.075 O 4 compounds, the T C decreases to 775 K, 812 K and 839 K respectively for Dy 3+ [7], Ho 3+ and Sm 3+ substitutions [8]. However, there are no concrete mechanisms and evidences to explain the decrease in magnetization and Curie temperature, even though qualitatively it has been attributed to weaker R-Fe exchange coupling replacing the stronger Fe-Fe exchange coupling [12,13].…”

“…The octahedra containing Fe 3+ ions in NFO, when partially substituted by rare-earth (R 3+ ), become non-centrosymmetric to make the compound ferroelectric. Experimentally it has been shown that, substituents like Sm 3+ and Ho 3+ induce magnetoelectric effect in NFO [8].…”

Microstructure, AC impedance and DC electrical conductivity characteristics of NiFe2-xGdxO4 (x = 0, 0.05 and 0.075)

“…[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] However, the efforts towards understanding the effect of the substitution of rare earth (R) ions in spinel oxides are meager. Engineering the materials and development of devices for high frequency applications based on nickel ferrites is clearly dependent upon the fundamental knowledge of electrical behavior of these materials.…”