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Magnetic studies in bulk 57% CuxZn1-xO/43% CuO composite prepared chemically with x=0.10 (0.03) are reported. Temperature dependence of the magnetic susceptibility shows clear signature of the Néel temperature TN≃230 K for pure CuO. Hysteresis loop studies in the zero-field-cooled sample show room-temperature ferromagnetism with coercivity Hc≃50 Oe at 300 K with strong temperature dependence for T<300 K. A negative exchange bias He at 5 K is observed when the sample is cooled from RT in H=20 kOe, and its temperature dependence yields He→0 at TN=230 K of CuO. These results and the temperature dependence of remanence Mr provide strong evidence that the CuxZn1-xO phase with x≃0.10 is a ferromagnet with Tc≃400 K. An electron magnetic resonance signal due to Cu2+ substituting for Zn2+ in CuxZn1-xO is also observed. [ABSTRACT FROM AUTHOR]

Experimental investigations of the magnetic dead layer in 7.6 nm thick film of La0.7Sr0.3MnO3 (LSMO) are reported. The dc magnetization (M) measurements for a sample cooled to T = 5 K in applied field H = 0 reveal the presence of negative remanent magnetization (NRM) in the M vs. H (magnetic field) measurements as well as in the M vs. T measurements in H = 50 Oe and 100 Oe. The M vs. T data in ZFC (zero-field-cooled) and FC (field-cooled) protocols are used to determine the blocking temperature TB in different H. Isothermal hysteresis loops at different T are used to determine the temperature dependence of saturation magnetization (MS), remanence (MR) and coercivity HC. The MS vs. T data are fit to the Bloch law, MS(T) = M0(1 – BT3/2), showing a good fit for T < 100 K and yielding the nearest-neighbor exchange constant J/kB ≅ 18 K. The variations of TB vs. H and HC vs. T are well described by the model often used for randomly oriented magnetic nanoparticles with magnetic domain diameter ≈ 9 nm present in the dead-layer of thickness d =1.4 nm. Finally, the data available from literature on the thickness (D) variation of Curie temperature (TC) and MS of LSMO films grown under 200, 150, and 0.38 mTorr pressures of O2 are analyzed in terms of the finite-size scaling, with MS vs. D data fit to MS(D) = MS(b)(1-d/D) yielding the dead layer thickness d = 1.1 nm, 1.4 nm and 2.4 nm respectively. Brief discussion on the significance of these results is presented. [ABSTRACT FROM AUTHOR]

In the present work we report multiferroic behavior in lead zirconate titanate (PZT)–cobalt iron oxide (CFO) composite thin films. It is found that upon annealing, the multilayered structures are intermixed at least partially, and CFO is phase separated into PZT matrix to form a composite film. The phase separation behavior has been characterized by x-ray photoelectron spectroscopy depth profiling of the constituent elements in conjunction with dielectric spectroscopy measurements. The composite films exhibited ferroelectric as well as ferromagnetic characteristics at room temperature. The coupling between the ferroelectric and the ferromagnetic order parameters has been demonstrated through the reduction of ferroelectric polarization when measured under an applied magnetic field. [ABSTRACT FROM AUTHOR]

Magnetic properties of sol-gel-prepared bulk samples of Co0.05Zn0.95O and Mn0.05Zn0.95O are reported before and after annealing in 5%H2/95%Ar at 573 K for 6 h. The as-prepared samples are paramagnetic with the magnetic susceptibility χ following the Curie-Weiss law: χ=χ0+C/(T-θ). The magnitudes of C are consistent with the magnetic moments expected for the Co2+ and Mn2+ states. After hydrogenation, the magnetism of Mn/ZnO is unchanged but Co/ZnO acquires room-temperature ferromagnetism (RTFM) with a magnetic moment of 0.35μB/Co site and hysteresis loop with coercivity Hc≃600 Oe, remanence Mr≃0.45 emu/g, and saturation magnetization Ms≃1.2 emu/g. Electron magnetic-resonance spectroscopy at 9.28 GHz gives signals corresponding to the Co2+ and Mn2+ states for the paramagnetic states and a broad FM signal for the hydrogenated Co/ZnO. This difference under hydrogenation between Co/ZnO and Mn/ZnO suggests that n-type doping leads to stabilizing of RTFM in Co/ZnO but not in Mn/ZnO, the latter perhaps requiring p-type doping. [ABSTRACT FROM AUTHOR]

Temperature variation (5 K–300 K) of the AC magnetic susceptibilities (χ′ and χ″) at frequency f=0.1, 1, 50, 100, 500, 1000, 2000, 5000, and 10, 000 Hz are reported in 5 nm diameter nanorods of NiO, with and without oleic acid (OA) coating. Using the peak in χ′ as the blocking temperature TB, it is observed that TB increases with increasing f. The data for the two samples fit the Vogel-Fulcher law: f=f0 exp[-Ea/k(TB-T0)], with f0=9.2×1011 Hz, Ea/k=1085 K, and T0=165 K (0 K) for the uncoated (coated) particles. This shows that T0 provides a good measure of the effects of interparticle interactions on magnetic relaxation and that these interactions are essentially eliminated with the OA coating. [ABSTRACT FROM AUTHOR]

Starting with 7 nm γFe2O3 nanoparticles, synthesis of DNA-γFe2O3 nanocomposite and its structural/magnetic properties vis-a-vis the parent γFe2O3 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-γFe2O3 nanocomposite. Transmission electron microscopy also shows an increase in size and a considerably wider size distribution. Temperature (5–300 K) variation of the magnetization (M) shows a wider distribution of the blocking temperatures (TB), as expected from the wider size distribution. Above TB, the data of M vs H fit the modified Langevin function with magnetic moment/particle μp≈11 000μB, somewhat larger than μp≈8000μB for the parent γFe2O3. However, M/g(γFe2O3) is not significantly affected. In electron magnetic-resonance spectroscopy at 9.28 GHz, only a single line is observed in DNA-γFe2O3 nanocomposite compared to two lines in γFe2O3. These effects are discussed in terms of the above structural differences. [ABSTRACT FROM AUTHOR]

We report that Co0.1Ti0.9O2-δ prepared by the sol-gel technique is a paramagnet following the Curie-Weiss law: x =x0+C/(T+θ) with θ≃5 K. However, hydrogenation at 673 K in H2/Ar (5%/95%) gas converts a part of the paramagnetic (P) sample to room temperature ferromagnet (RTFM) and reheating the sample at 573 K in air converts it back to a paramagnet completely. This reversible P⇄RTFM transition has been observed for additional cycles by alternately heating in air and H2/Ar. It is argued that this RTFM is intrinsic and it is due to Co2+-Co2+ exchange interaction mediated by oxygen holes which are produced by hydrogenation but eliminated by oxidation. [ABSTRACT FROM AUTHOR]

Samples of Co[sub 0.1]Ti[sub 0.9]O[sub 2-δ] (anatase) prepared by the sol–gel technique are found to be paramagnetic at room temperature, with the magnetic susceptibility following Curie–Weiss law in the investigated range of 2–370 K. However, transformation from paramagnetism to room-temperature ferromagnetism (RTFM) is observed by hydrogenation of the sample at 573 K. The increase in the hydrogenation time from 1 to 6 h increases the remanance, and the Curie temperature ≃470 K is determined by extrapolation. 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. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report detailed studies of magnetization (M) as a function of magnetic field H (up to 50 kOe) and temperature T (5-380 K) in x% (Co/TiO[SUB2] (rutile) films for x=1, 4, 6, 10, and 12. These films, prepared by sputtering, show room temperature ferromagnetism (RTFM). Measurements of M vs T at H=50 Oe reported here in zero-field-cooled (ZFC) and field-cooled (FC) cases show M peaking at T[SUBp] ≃ 30 K for 1% Co to T[SUBp] ≃ 125 K for 12% Co doped films whereas bifurcation of the FC and ZFC data is observed near 300 K. For T

The in-plane angular variation of hysteretic ferromagnetic resonance (HFMR) at 9.57 GHz, in increasing and decreasing field sweeps, is used to determine both coercivity H[sub C] and exchange bias H[sub E], in a ferromagnetic/antiferromagnetic Co/MnPt bilayer. The angular dependence of H[sub C] and H[sub E], is in excellent agreement with micromagnetic models in which the interfacial exchange energy is approximately equal to the domain-wall energy in the antiferromagnet. The HFMR linewidths show a systematic angular variation, indicating that domain formation is important. [ABSTRACT FROM AUTHOR]

In the 6.6 nm particles of CuO with Néel temperature T[sub N]...40 K, hysteresis loops are observed up to 330 K. With decrease in temperature, the coercivity H[sub c] increases slowly up to T[sub N] below which rapid increases in H[sub c] and exchange bias He are observed. At 5 K, the ratio H[sub e]/H[sub c]...2, decreasing to zero as T → T[sub N]. At 10 K, the variation of H[sub e], H[sub c], and the ratio H[sub e]/H[sub c] with the cooling field show behavior similar to that of the weak ferromagnetic moment resulting from the uncompensated surface spins. [ABSTRACT FROM AUTHOR]

We have investigated Co-doped TiO[sub 2] thin films grown by reactive co-sputtering. X-ray diffraction showed a single phase polycrystalline rutile structure, without any segregation of Co into particulates within the instrumental resolution limit. The atomic content of Co ranged from 1% to 12%. The temperature dependence of resistivity showed an extrinsic semiconducting behavior. From optical absorption measurements, the band gap E[sub g] ≈ 3.2 5 ± 0.0 5 eV was found, independent of the Co concentration, and in agreement with a literature value. Room temperature M-H loops showed a ferromagnetic behavior for Co content higher than 3%. The magnetic moment per Co atom was estimated to be about 0.94 µ[sub B], suggesting a low spin configuration of Co ions. The temperature dependence of remanent magnetization revealed a Curie temperature higher than 400 K for Co content of 12%. [ABSTRACT FROM AUTHOR]

Presents observations on magnetization reversal and superparamagnetic behavior for films of copper ferrite sputtered in an oxygen atmosphere. Composition of nanocrystals found after x-ray diffraction studies; Analysis of the temperature dependence of the film magnetization for zero-field-cooled and field-cooled; Static magnetic field dependence of the magnetization for CuFe[sub2]O[sub4] films at 5 and 300 Kelvin.

Discusses a study on amorphous thin films of bismuth-iron-oxygen-lead-zirconium-oxygen. Techniques used to prepare the films; Effects of sputtering conditions and annealing at high temperature on magnetic properties of such films; Analysis of the room-temperature magnetization.

Deals with a study on the magnetic properties of an intermetallic when mischmetal is used as the rare-earth component for both a hydrided and unhydrided compound in the case of mischmetal nickel-iron intermetallic. Mössbauer effect measurements; Findings of scanning electron microscopy; Assessment of the hybriding process of iron.

Details a study which analyzed the structural and magnetic characteristics of radio frequency sputtered thin films of La[sub0.74]Pb[sub0.26]MnO[subz] on silicon. Methodology of the study; Measurement of magnetization properties; Temperature dependence of magnetization.

Provides information on a study that investigated the nature of magnetism and electron paramagnetic resonance spin dynamics in iron oxyhydroxide particles. Experimental procedures; Results and discussion.