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The nature of magnetic ordering in the inverted spinel Co2SnO4 = [Co2+][Co2+Sn4+]O4 is investigated by measuring the temperature dependence of its magnetization (M) and ac-susceptibilities (χ′ and χ″) in different magnetic fields (H) using a superconducting quantum interference device magnetometer. The polycrystalline sample with a grain size of 3-5 μm was prepared by the solid-state route and characterized by x-ray diffraction and scanning electron microscopy. Above the ferrimagnetic Néel temperature TN = 41 K, χdc = M/H fits well with the Néel' expression for the two-sublattice model of ferrimagnetism. The ferrimagnetic ordering is suggested to result from different magnetic moments of Co2+ on the A sites (3.87 μB) and B sites (4.16 μB) and antiferromagnetic molecular field constants with magnitudes NAA = 13.6, NBB = 36.8, and NAB = 33.2. The temperature variations of χ′ and χ″ under various dc-bias fields suggest the existence of a spin-glass (SG) phase for T < TSG = 39.1 K in which only the transverse spin components are frozen below TSG. This co-existence of longitudinal ferrimagnetic order below TN = 41 K and transverse SG state below TSG = 39.1 K is suggested to result from the presence of non-magnetic Sn4+ ions on the B sites. [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]

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 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

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.

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.

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.

Synthesis and nature of magnetism in ZnMnO3 nanoparticles with cubic spinel structure (a = 8.369 Å and size D ≃ 25 nm) are reported. Magnetization M vs. H and M vs. T data yield ferrimagnetism with TN ≃ 20 K, μ/Mn = 4.46 μB, MS ≃ 18.5 emu/g, and a transition at TS ≃ 7 K. For T < TN, coercivity and exchange-bias approach zero at TN with anomaly at TS. Using magnetic data and simulations, structure of [Zn2+][1/3]O11/3 with antiparallel moments of Mn4+ and Mn3+ is proposed. [ABSTRACT FROM AUTHOR]

Results of the characterization of six Co-based Fischer–Tropsch (FT) catalysts, with 15% Co loading and supported on SiO2 and Al2O3, are presented. Room temperature X-ray diffraction (XRD), temperature and magnetic field (H) variation of the magnetization (M), and low-temperature (5 K) electron magnetic resonance (EMR) are used for determining the electronic states (Co0, CoO, Co3O4, Co2+) of cobalt. Performance of these catalysts for FT synthesis is tested at reaction temperature of 240 °C and pressure of 20 bars. Under these conditions, 15% Co/SiO2 catalysts yield higher CO and syngas conversions with higher methane selectivity than 15% Co/Al2O3 catalysts. Conversely the Al2O3 supported catalysts gave much higher selectivity towards olefins than Co/SiO2. These results yield the correlation that the presence of Co3O4 yield higher methane selectivity whereas the presence of Co2+ species yields lower methane selectivity but higher olefin selectivity. The activities and selectivities are found to be stable for 55 h on-stream. [ABSTRACT FROM AUTHOR]

Synthesis and magnetic properties of nanocrystals (size ≃22 nm) of cubic spinel MgMnO3 with the defect structure [Mg2+][Mg1/32+Mn4/34+□1/3]O4 are reported. Analysis of the magnetization M versus T (2–370 K) and M versus H (up to 65 kOe) data shows a blocking temperature TB≃11 K and an estimated Néel temperature TN∼150 K above which the Weiss temperature θ=-7 K and μ=3.91 μB/Mn4+. For TB

Synthesis and magnetic properties of nanocrystals (size ≃22 nm) of cubic spinel MgMnO3 with the defect structure [Mg2+][Mg1/32+Mn4/34+□1/3]O4 are reported. Analysis of the magnetization M versus T (2–370 K) and M versus H (up to 65 kOe) data shows a blocking temperature TB≃11 K and an estimated Néel temperature TN∼150 K above which the Weiss temperature θ=-7 K and μ=3.91 μB/Mn4+. For TBN, fit of the M versus H data to modified Langevin function yields 35 μB as magnetic moment/particle, resulting from the defect structure. [ABSTRACT FROM AUTHOR]

Magnetic properties of Li0.5Mg0.5MnO3-δ nanoparticles (size ≃ 20 nm) synthesized by the Pechini method are investigated using temperature dependence of its magnetization (M) and electron magnetic resonance (EMR) spectra at 9.286 GHz. Analysis of the x-ray diffraction spectra yields its structure to be a cubic defect spinel with the formula 4(Li0.5Mg0.5MnO2.75) = 3{[Li2/3Mg1/3][Mn4/3Mg1/3[larger_open_square]1/3]O11/3]} so that Mn occupies the octahedral B-sites only. The data of M versus T yields a blocking temperature TB ≃ 9 K above which the Curie-Weiss law variation with θ = 13 K and μ = 3.96μB characteristic of Mn4+ ions is established. For T < 9 K, temperature dependent coercivity and remanence are observed. The observed temperature dependence of the EMR parameters (linewidth ΔH, resonance field Hr, and intensity Io) for T < 30 K is interpreted in terms of TB (EMR) ≃ 30 K. Formation of ferromagnetic Mn4+ clusters, resulting from the co-presence of non-magnetic Mg2+ and vacancies on the B-sites, is inferred. [ABSTRACT FROM AUTHOR]

Magnetic properties of 5.5 nm CuxCe1-xO2 nanoparticles (NPs) with change in Cu doping (x = 0, 2.5, 5.0, 7.5, and 10%) are investigated to examine the controversial issue of room temperature ferromagnetism (FM) in this system. The data of magnetization M versus magnetic field H fit the equation: M = Mf + χpH with Mf (χp) being the FM (paramagnetic) part. The observed FM saturation magnetization MS = 8.5 × 10-5 emu/g for x = 0 is suggested to be due to Fe impurities detected in the samples at 20 ppm level. However, in the doped samples, both χp and MS increase nearly linearly with x with the FM magnetic moment μS ≈ 3 × 10-4μB/Cu atom. This magnitude of μS, although considerably smaller than μS ≈ 1 μB/Cu atom reported in thin films of CuxCe1-xO2, is argued to be an intrinsic effect due to Cu doping. Electron magnetic resonance studies show lines due to Cu2+ ions in the doped samples. [ABSTRACT FROM AUTHOR]