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Composites of NiFe2O4 (NFO)–BaTiO3 (BTO) and NiGd0.01Fe1.99O4 (G0.01)–BTO were investigated by x-ray diffraction, magnetization, transmission electron microscopy, magnetocapacitance, and ferroelectric studies. NFO and G0.01 nanoparticles were synthesized by the sol-gel method. The crystallite size of the nanoparticles estimated from the x-ray diffraction patterns is 20–22 nm. The average crystallite sizes of NFO and G0.01 nanoparticles were estimated from the transmission electron micrographs as 26 (1) nm and 22.3 (0.3) nm, respectively. These nanoparticles were encapsulated in a BTO shell, resulting in the formation of nanocomposites. Room temperature magnetization (at 60 kOe) of G0.01 nanoparticles was found to be slightly higher than that of NFO nanoparticles, due to the larger moment of Gd3+ than that of Fe3+. Also, the magnetization of G0.01–BTO is more than that of NFO–BTO nanocomposites. The magnetoelectric effect was observed with a magnetocapacitance value of approximately −10% at 10 kHz in both the composites. [ABSTRACT FROM AUTHOR]

Magnetic and electrical transport studies have been carried out on [Ho.sub.0.85][Tb.sub.0.15][Fe.sub.2-x][Mn.sub.x] [x = 0-2] in the temperature range 5-300 K. The saturation magnetization at 5 K is found to increase with increasing Mn content due to the absence of Mn moments. The temperature variation of magnetization reveals several spin reorientation transitions and these are compared with the ac susceptibility results. Electrical resisitvity reveals the dominance of electron magnon scattering at low temperatures and electron-phonon scattering at high temperatures. Index Terms--Electrical resistivity, magnetic materials, magnetization process, rare-earth iron compounds.

The structural and magnetic properties of Co substituted [([Sm.sub.0.4][Pr.sub.0.6]).sub.3] [([Fe.sub.1-x][Co.sub.x]).sub.27.5[Ti.sub.1.5] [x = 0.1, 0.2, 0.3, 0.4] compounds have been studied through powder X-ray diffraction (XRD) and magnetization measurements. All the compounds have formed in monoclinic [Ra.sub.3][(Fe,M).sub.29] phase with A2/m space group. The unit cell volume decreases with Co concentration in accordance with its size. The magnetization at room temperature increases with Co substitution and is qualitatively explained on the basis of rigid band approximation. Curie temperature is also found to increase with Co concentration. XRD patterns on the magnetically oriented samples reveal that nearly axial anisotropy is obtained for the x = 0.4 compound and that the easy magnetization direction (EMD) is along [2 0 4]. Index Terms--Axial anisotropy, cobalt substituted R-TM intermetallics, permanent magnet materials.

The structural and magnetic properties of YGd[Fe.sub.17-x][Co.sub.x] Ga (x = 0, 1, 2 and 3) have been investigated through X-ray diffraction and magnetization studies. All the compounds up to x = 0.2 are formed in a single-phase, hexagonal structure. The unit cell volume decreased with the addition of Co due to the smaller size of Co than that of Fe. The magnetization and Curie-temperature values are found to increase with the addition of x and could be due to the additional Co-Co, Fe-Co exchange whose magnitude is larger compared to that of Fe-Fe exchange. Magnetically aligned sample powders indicate the presence of planar anisotropy for all the compounds. Index Terms--Curie temperature, intermetallics, magnetization.

The structural and magnetic properties of [Gd.sub.3][([Fe.sub.-x][Al.sub.x]).sub.27.5][Ti.1.5] (0.1-0.4) have been investigated by X-ray diffraction (XRD), magnetization and Curie temperature ([T.sub.c]) measurements. All the compounds have formed in [Nd.sub.3] [(Fe,Ti).sub.29] (3:29) type structure with Gd[(Fe,Ti).sub.12] (1:12) phase as the secondary phase and traces of [alpha]-Fe. The unit cell parameters increase anisotropically with the Al content. The saturation magnetization decreases with increasing Al and is attributed to the magntovolume effect and the modification of the density of states (DOS). The increase of Curie temperature up to x = 0.3 and subsequent decrease is explained on the basis of band narrowing. The easy direction of magnetization (EMD) is away from the ab-plane up to x = 0.3 changes to along ab-plane for x = 0.4. Index Terms--3:29 compounds, anisotropy, Curie temperature, magnetization.