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The influence of the lanthanum (La) substitution on structural, electrical and magnetic properties of bismuth ferrite ceramics in a wide range of temperature and frequency is investigated. The results reveal that the changes in the magnetic factors with La doping and the electron magnetic resonance parameters are measured at 300 K and 9.28 GHz with respect to increase in the magnetic anisotropy and magnetization.

SQUID magnetometry and electron magnetic resonance (EMR) spectroscopy at 9.28 GHz were employed to probe magnetism and surface spin disorder in nanoparticles. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis showed magnetite particles with size [??]8 nm. Magnetization (M) versus temperature studies yielded blocking temperature [T.sub.B] [??] 170 K in H = 50 Oe. For T > [T.sub.B], M scales approximately as H/T with [??] 5400/[[micro].sub.B] as the magnetic moment/particle. At 5 K, the magnitudes of hysteresis loop parameters viz. coercivity [H.sub.c][??]37 Oe and saturation magnetization [M.sub.s] = 62 emu/g are considerably smaller than the reported values for larger 150 nm [Fe.sub.3][O.sub.4] particles. In EMR studies, a single symmetric line at g [??]2.11 with linewidth [DELTA]H = 850 Oe is observed at 300 K with the g-value and AH increasing with decreasing T. These results are interpreted in terms of a disordered surface spin layer of 0.5 nm thickness. Index Terms--Electron magnetic resonance, magnetic nanoparticles, magnetometry, superparamagnetism.

In this paper, we compare the magnetic relaxation of DNA-coated [gamma][Fe.sub.2][O.sub.3] with that of parent 7-nm [gamma][Fe.sub.2][O.sub.3] particles by measuring the temperature dependence of AC susceptibilities (X' and X') at frequency f = 0.1, 1, 10, 100, and 1000 Hz and electron magnetic resonance (EMR) at 9.28 GHz. Changes in the blocking temperature [T.sub.B] (where X' peaks) with frequency are analyzed using the relation: [T.sub.B] = [T.sub.o] + [[T.sub.a]/ln(fo/f)] derived from Vogel-Fulcher relaxation, where [T.sub.a]([T.sub.o]) measures the effective energy barrier (interparticle interaction). The fit to the data yields fo = 1.3 x [10.sup.16] Hz, [T.sub.a] = 2760 K(2960 K), and [T.sub.o] = 40 K(20 K) for the uncoated (DNA-coated) [gamma][Fe.sub.2][O.sub.3]. From the relative shift [DELTA][T.sub.m] of [T.sub.m] (the temperature where X' peaks) with change [DELTA] log f in frequency, the parameter[PHI] = [DELTA][T.sub.m]/([T.sub.m] [DELTA]log f) is determined to be 0.04(0.06) for the uncoated (coated) [gamma][Fe.sub.2][O.sub.3]. These results show only minimal changes in the magnetic dynamics of [gamma][Fe.sub.2][O.sub.3] upon DNA coating. Index Terms--Biocompatibility, electron magnetic resonance, magnetic nanoparticles, magnetic relaxation.

Transformation from paramagnetism to room-temperature ferromagnetism (RTFM) is observed by hydrogenation of the samples at 573 K. X-ray photoelectron spectroscopy and transmission electron microscopy of the hydrogenated samples failed to detect Co nanoparticles, suggesting that the observed RTFM in the hydrogenated samples may be intrinsic.

The Co-doped TiO2 films grown by reactive co-sputtering are examined. A magnetic moment of 0.94 mu B per Co atom and a ferromagnetic behavior above 400 K is observed in the Co-doped TiO2 films.

Copper ferrite films subjected to sputtering in an oxygen atmosphere reveal magnetization reversal and superparamagnetic behavior. The zero-field cooled and field-cooled curves are inversely proportional to static field strength. Copper ferrite films contain 14-nanometer nanoscale CuFe2O4 crystals.

A study of the magnetism and spin dynamics of nanoscale FeOOH particles, that were not based on either alpha-FeOOH or alpha-Fe2O3, revealed that the particles were transformed to Fe3O4 (alpha-Fe2O3) on heating in vacuum at 800 K. These superparamagnetic nanoscale particles, which were studied at various temperatures, revealed thermal motion.

The article presents a comparative analysis of the structural, as well as the magnetic properties of the [alpha]-Ni[(OH).sub.2] and [beta]-Ni[(OH).sub.2] compounds. The magnetism of these compounds is shown to be completely dependent on the temperatures, as well as the magnetic fields.

Temperature dependence of ac susceptibilities [[zeta].sup.I] and [[zeta].sup.II] are described by using frequencies for nanoparticles of Ni dispersed in silica (Ni/Si[O.sub.2]) with the mean sizes, as determined by transmission electron microscopy. The blocking temperatures [T.sub.B] are fit to the Vogel-Fulcher law and the validity of result is checked and the calculated values are consistent with experimental values.

The magnetic properties of oleic acid/oleylamine coated magnetite nanoparticles of average diameter (D = 4, 6, 8, 10 and 12) are analyzed. These samples are characterized by using x-ray diffraction (XRD) and transmission electron microscopy with XRD showing increasing disorder with decreasing D.

The variations of the blocking temperature [T.sub.B] with measuring frequency [f.sub.m] and applied field H are described for Ni nanoparticles (NPs) embedded in Si[O.sub.2] matrix with the nominal composition Ni/Si[O.sub.2]. The obtained results are compared with the predictions of the Neel-Brown model of magnetic relaxation in noninteracting NPs.

The nature of magnetism in Cu-doped Zr[O.sub.2], Ti[O.sub.2], MgO, Si[O.sub.2] and [Al.sub.2][O.sub.3] is examined by using superconducting quantum interference device magnetometry and electron magnetic resonance (EMR). Magnetic field and temperature dependences of the magnetization have shown only paramagnetism in these oxides in contrast to ferromagnetism seen in Cu/ZnO.

A bulk [Cu.sub.x][Zn.sub.1-x]O/CuO composite prepared by the gel-coprecipitation method is studied for testing room temperature ferromagnetism (RTFM) in a bulk sample sample of a [Zn.sub.1-x][Cu.sub.x]O. The temperature dependence of remanence has shown that the [Cu.sub.x][Zn.sub.1-x]O phase is a ferromagnet.

The multiferroic behavior of the lead zirconate titanate (PZT)-cobalt iron oxide (CFO) composite thin films, which are formed by annealing the multilayered structures, is analyzed. The films exhibit a reduction in the ferroelectric polarization on being subjected to a magnetic field and hence demonstrate the coupling between the ferroelectric and ferromagnetic order parameters of the materials.

Starting with 7 nm gammaFe2O3 nanoparticles, synthesis of DNA-gammaFe2O3 nanocomposite and its structural/magnetic properties are reported. Analysis of the x-ray diffraction shows an increase in the particle strain and average particle size (to 9.7 nm) in DNA-gammaFe2O3 nanocomposite.

Temperature variation (5 Kelvin-300K) of the AC magnetic susceptibilities (X' and X'') at frequency f =0.1. 1.50, 100, 500, 1000, 2000, 5000, and 10,000 Hz are studied in 5 nm diameter nanorods of NiO, with and without oleic acid coating. [T.sub.B] is observed to vary directly with f, when the peak in X' is used as the blocking temperature.

[Co.sub.0.05][Zn.sub.0.95]O and [Mn.sub.0.05][Zn.sub.0.95]O were prepared by the technique of sol-gel synthesis, which allows mixing of the chemicals at atomic level thus reducing the possibility of undetectable impurity phases. Magnetic studies of the annealed samples reveal that they are paramagnetic with their magnetic susceptibility chi following the Curie-Weiss law.

A report is presented on the synthesis of sol-gel derived lead iron niobate (Pb1.10(Fe0.5Nb0.5)O3)(PFN) powders and their characteristics in terms of their dielectric and magnetic properties to establish their multiferroic nature. It is identified that a very narrow process window exists to yield calcined phase pure perovskite PFN powder of monoclinic structure.

A report that room temperature ferromagnet (RFTM) in the hydrogenated sample is reversible to paramagnetism if the sample is reheated in air at 573 K and subsequent hydrogenation at 673 K produces RFTM again, is presented. It is argued that this RTFM is intrinsic and it is due to Co9super 2+)-Co(super 2+) exchange interaction mediated by oxygen holes which are produced by hydrogenation but eliminated by oxidation.

The room temperature ferromagnetism (RFTM) was seen in the Co/TiO2 (rutile) films, which was prepared by sputtering, and the magnetism (M) as a magnetic field H and temperature T in x% Co/TiO2 (rutile) films for x=1, 4, 6, 10 and 12 is studied. The x-ray diffraction (XRD) studies show that a fraction of Co does substitute for Ti in Co(sub x)Ti(sub 1-x)O(sub 2) and due to the interference from Co nanoparticles, the RFTM of Co(sub x)Ti(sub 1-x)O(sub 2) could not be established for the lightly doped samples.

The in-plane angular variation of hysteretic ferromagnetic resonance (HFMR) is used to determine both coercivity H(sub C) and exchange bias H(sub E) in a ferromagnetic/antiferromagnetic Co/MnPt bilayer. Application of HFMR technique to other F/AF systems and interpretation of the angular variation of the line width could yield further information on the nature of interface magnetic interactions.