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Structural and magnetic properties of Fe/Pt core-shell nanostructure prepared by a sequential reduction process are reported. Transmission electron microscopy shows nearly spherical particles fitting a lognormal size distribution with Do=3.0 nm and distribution width λD=0.31. In x-ray diffraction, Bragg lines only from the Pt shell are clearly identified with line-widths yielding crystallite size=3.1 nm. Measurements of magnetization M vs. T (2K-350K) in magnetic fields up to 90 kOe show a blocking temperature TB=13K below which hysteresis loops are observed with coercivity HC increasing with decreasing T reaching HC=750Oe at 2 K. Temperature dependence of the ac susceptibilities at frequencies fm=10 Hz-5 kHz is measured to determine the change in TB with fm using the Vogel-Fulcher law. This analysis shows the presence of significant interparticle interaction, the Neel-Brown relaxation frequency fo=5.3×1010Hz and anisotropy constant Ka=3.6×106 ergs/ cm3. A fit of the M vs. H data up to H=90 kOe for T>TB to the modified Langevin function taking particle size distribution into account yields magnetic moment per particle consistent with the proposed core-shell structure; Fe core of 2.2 nm diameter and Pt shell of 0.4 nm thickness. [ABSTRACT FROM AUTHOR]

The optoelectronic and piezoelectric properties of AlN:Er thin films have been of great recent interest for potential device applications. In this work, the focus is on the electronic state of Er in AlN:Er thin films prepared by reactive magnetron sputtering on (001) p-type Si substrate. X-ray diffraction shows that Er doping expands the lattice and the AlN:Er film has preferential c-plane orientation. To determine whether Er in AlN:Er is present as Er metal, Er2O3, or Er3+ substituting for Al3+, detailed measurements and analysis of the temperature dependence (2 K-300 K) of the magnetization M at a fixed magnetic field H along with the M vs. H data at 2K up to H=90 kOe are presented. The presence of Er2O3 and Er metal is ruled out since their characteristic magnetic transitions are not observed in the AlN:Er sample. Instead, the observed M vs. T and M vs. H variations are consistent with Er present as Er3+ substituting for Al3+ in AlN:Er at a concentration x=1.08% in agreement with x=0.94%60.20% determined using x-ray photoelectron spectroscopy (XPS). The larger size of Er3+ vs. Al3+explains the observed lattice expansion of AlN:Er. [ABSTRACT FROM AUTHOR]

Photoluminescence spectra of YVO4:Eu3+ nanoparticles are presented, with and without the attachment of organic molecules that are proposed for linking to biomolecules. YVO4:Eu3+ nanoparticles with 5% dopant concentration were synthesized via wet chemical synthesis. X-ray diffraction and transmission electron microscopy show the expected wakefieldite structure of tetragonal particles with an average size of 17 nm. Fourier-transform infrared spectroscopy determines that metal-carboxylate coordination is successful in replacing native metal-hydroxyl bonds with three organic linkers, namely, benzoic acid, 3-nitro 4-chloro-benzoic acid, and 3,4-dihydroxybenzoic acid, in separate treatments. UV-excitation photoluminescence spectra show that the position and intensity of the dominant 5D0 - 7F2 electric-dipole transition at 619 nm are unaffected by the benzoic acid and 3-nitro 4-chloro-benzoic acid treatments. Attachment of 3,4-dihydroxybenzoic acid produces an order-of-magnitude quenching in the photoluminescence, due to the presence of high-frequency vibrational modes in the linker. Ratios of the dominant electric- and magnetic-dipole transitions confirm infrared measurements, which indicate that the bulk crystal of the nanoparticle is unchanged by all three treatments. [ABSTRACT FROM AUTHOR]

Bulk NiO is a well-known antiferromagnet with Neel temperature TN(∞) = 524 K and an optical band-gap Eg = 4.3 eV. With decrease in particle size D from 40 nm to 4 nm of NiO, systematic changes of TN and Eg are observed and discussed here. From magnetic measurements, the changes in TN with D are found to fit finite-size scaling equation TN(D) = TN(∞) [1 - (ξo/D)λ] with λ = 3.2 ± 0.5 and ξo = 3.2 ± 0.2 nm, in good agreement with the predictions for a Heisenberg system. The observed blue shifts of Eg with decrease in D reaching Eg = 5.12 eV for D ∼ 4 nm are likely due to quantum confinement and non-stoichiometry. [ABSTRACT FROM AUTHOR]

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]

Magnetic properties of bulk MgMnO3, a cubic defect spinel with the structure 4MgMnO3=3[Mg2+][Mg+2 1/3Mn4+ 4/3□1/3]O4, are reported. For T > 150 K, magnetization M vs T data fits the Curie-Weiss law with μ ≃ 4μB expected for Mn4+ and θ ≃ -40 K indicating antiferromagnetic Mn4+-Mn4+coupling. For T < 150 K, a blocking temperature TB ≃ 15 K is observed below which coercivity increases with decreasing T. The electron magnetic resonance spectra yield a single broad line with g ≃ 1.9 whose linewidth increases with decreasing T leading to a peak at TB. As predicted in spinels with magnetic ions only on the B-sites, these observations suggest a magnetically frustrated state with short-range order only. [ABSTRACT FROM AUTHOR]

The coexistence of the magnetic and the electrical properties in lanthanum (La)-modified bismuth ferrite (Bi1-xLaxFeO3, x=0.05, 0.1, 0.15, and 0.2) ceramics was studied and compared with those of bismuth ferrite (BiFeO3). The presence of a small secondary phase of BiFeO3 (arises due to excess Bi2O3) was removed on La substitution at the Bi site, as observed in x-ray diffraction (XRD). The effect of La substitution on dielectric constant, loss tangent, and remnant polarization of the samples was studied in a wide range of temperature (77–400 K) and frequency (1 kHz–1 MHz). The variation of magnetization, coercive field, and exchange bias with temperature (2–300 K) and La concentration were investigated. These changes in the magnetic parameters with La doping along with those of the electron magnetic resonance parameters measured at 300 K and 9.28 GHz are understood in terms of increase in the magnetic anisotropy and magnetization. These results also show that stabilization of crystal structure and nonuniformity in spin cycloid structure by La substitution enhances the multiferroic properties of BiFeO3. [ABSTRACT FROM AUTHOR]

In this work, we report the synthesis of sol-gel-derived lead iron niobate [Pb1.10(Fe0.5Nb0.5)O3] (PFN) powders and sintered ceramics. The PFN powders were calcined at (Ta), 973, 1073, 1173, 1273, and 1373 K for 3 h in air. As envisaged from x-ray-diffraction analyses, PFN powder calcined at 1173 K was crystallized into pure monoclinic perovskite phase whereas powders calcined at all other temperatures had varied amounts of retained pyrochlore (Pb3Nb4O13) phase coexisted with dominant monoclinic perovskite phase. The PFN pellet (prepared using the phase pure powder calcined at 1173 K) sintered at 1373 K for 4 h in air also had a minute quantity of retained pyrochlore phase coexisting with desired perovskite phase. From the temperature dependence of measured capacitance and loss tangent at different frequencies, the ferroelectric to paraelectric phase-transition temperature of PFN ceramics was observed at Tc≈370 K. The diffused nature of this transition and high dielectric constant of PFN is related to the cation disorder at the B site of A(BI+3BII+5)O3 lattice. For PFN powders, calcined at different temperatures, the temperature dependence of the magnetic susceptibility (χ) was measured in a temperature range of 2–360 K, whereas the magnetic hysteresis loops and electron magnetic resonance (EMR) spectra were measured at room temperature. Room-temperature ferromagnetism is observed in all the calcined powder samples and it was found that the magnetization increases with the increase in calcination temperature (Ta). The symmetric EMR line shape with g≈2.01 observed in all calcined samples was identified to be due to Fe3+ ions. It is suggested that the observed weak ferromagnetism, which increases with an increase in Ta, may be due to canting of the Fe3+ spins. These observations suggest PFN to be a very attractive single-phase ferroelectric/ferromagnetic material for room-temperature applications. [ABSTRACT FROM AUTHOR]

For the two stable phases of Ni(OH)2, viz. α-Ni(OH)2 and β-Ni(OH)2, structural and magnetic properties are compared employing x-ray diffraction (XRD), scanning electron microscopy/transmission electron microscopy (TEM/SEM), and variation of the magnetization (M) with temperatures (2-350 K) and magnetic fields (up to ≈65 kOe). Both phases crystallize in the layered hexagonal structure with a=3.04 Å (3.12 Å) and c=23.6 Å (4.67 Å) for the α(β) phase with clear evidence for turbostraticity in the α-phase. From TEM/SEM, the β-phase consists of nanoplates of dimensions 30(10)×3(1) nm, whereas the α-phase has flowerlike morphology with petal thickness ≈5(1) nm. The low-field M versus T data for the zero-field-cooled/field cooled cases bifurcates at Tp=25 K (13 K) for the β(α) phase. For T>Tp, Curie-Weiss variation of M versus T is observed yielding positive θ=20.6 K (32 K) with μ=2.95 μB (3.13 μB) for the Ni2+ ions in the β(α) phase. The M versus H data at 2 K shows antiferromagnetic (ferromagnetic) like variation for the β(α) phase with dM/dH showing peaks at Hc1=28 kOe and Hc2=55 kOe for the β-phase. It is concluded that β-Ni(OH)2 is a metamagnet for T

For the two stable phases of Ni(OH)2, viz. α-Ni(OH)2 and β-Ni(OH)2, structural and magnetic properties are compared employing x-ray diffraction (XRD), scanning electron microscopy/transmission electron microscopy (TEM/SEM), and variation of the magnetization (M) with temperatures (2-350 K) and magnetic fields (up to ≈65 kOe). Both phases crystallize in the layered hexagonal structure with a=3.04 Å (3.12 Å) and c=23.6 Å (4.67 Å) for the α(β) phase with clear evidence for turbostraticity in the α-phase. From TEM/SEM, the β-phase consists of nanoplates of dimensions 30(10)×3(1) nm, whereas the α-phase has flowerlike morphology with petal thickness ≈5(1) nm. The low-field M versus T data for the zero-field-cooled/field cooled cases bifurcates at Tp=25 K (13 K) for the β(α) phase. For T>Tp, Curie-Weiss variation of M versus T is observed yielding positive θ=20.6 K (32 K) with μ=2.95 μB (3.13 μB) for the Ni2+ ions in the β(α) phase. The M versus H data at 2 K shows antiferromagnetic (ferromagnetic) like variation for the β(α) phase with dM/dH showing peaks at Hc1=28 kOe and Hc2=55 kOe for the β-phase. It is concluded that β-Ni(OH)2 is a metamagnet for T2 is a hard ferromagnet with Tc=13 K and domain structure for H<5 kOe. [ABSTRACT FROM AUTHOR]

Temperature dependence of ac susceptibilities χ′ and χ″ are reported using frequencies fm=0.1, 1, 99, 499, and 997 Hz for nanoparticles of Ni dispersed in silica (Ni/SiO2:15/85) with the mean sizes D=3.8, 11.7, 15, and 21 nm (σ≃0.2 nm), as determined by transmission electron microscopy. The blocking temperatures TB, as determined by peaks in χ″ versus T data, are fit to the Vogel–Fulcher law based on the following equation: TB=To+Ta/ln(fo/fm). Using the attempt frequency fo=1.82×1010 Hz, Ta (K)=310 (21), 954(17), 1334(14), and 1405(47) are determined for D=3.8, 11.7, 15, and 21 nm, respectively, along with To (representing the interparticle interaction)=0, 0, 6.6(0.7), and 12.5(2.5) K respectively. The magnitudes of Ta=KaV/k yield the anisotropy constant Ka increasing with decreasing D (or volume V) due to contributions from surface anisotropy. The validity of the theoretical result χ″=C∂(χ′T)/∂T with C≃π/[2 ln(fo/2πfm)] is checked and the calculated values of fo are consistent with experimental value of fo=1.82×1010 Hz. [ABSTRACT FROM AUTHOR]

Magnetic properties of oleic acid/oleylamine coated magnetite nanoparticles of average diameter D=4, 6, 8, 10, and 12 nm are reported. The samples were characterized by transmission electron microscopy and x-ray diffraction (XRD) with XRD showing increasing disorder with decreasing D. Magnetization M vs temperature T data show the blocking temperature TB decreasing with decreasing D from TB=38 K for 12 nm to TB=6.5 K for D=4 nm. The saturation magnetization Ms at 2 K also decreases from Ms=62 emu/g for 12 nm to Ms=17 emu/g for 4 nm but the coercivity at 2 K increases with a decrease in D. It is shown that Ms fits Ms=92(1-2d/D)3 with d=0.68 nm for D>4 nm and d=0.86 for D=4 nm. This equation is derived assuming a core-shell model with shell of thickness d consisting of disordered spins not contributing to Ms. [ABSTRACT FROM AUTHOR]

The nature of magnetism in 10% Cu-doped ZrO2, TiO2, MgO, SiO2, and Al2O3 is investigated using superconducting quantum interference device magnetometry and electron magnetic resonance (EMR). The doping was done by the incipient wetness impregnation technique. X-ray diffraction studies showed the presence of some CuO notably in TiO2, SiO2, and Al2O3. However, EMR yielded typical Cu2+ spectra in all the samples, resulting from some doping. Magnetic field (H) and temperature (T) dependences of the magnetization (M) show only paramagnetism in these oxides in contrast to ferromagnetism with Tc=380 K observed in Cu/ZnO. Concentrations x of Cu2+ doped into the oxides are determined from the M vs T and M vs H data, showing Cu/ZrO2 with the largest x and hence largest magnetization. [ABSTRACT FROM AUTHOR]

The variations of the blocking temperature TB with measuring frequency fm and applied field H are reported for Ni nanoparticles (NPs) embedded in SiO2 matrix with the nominal composition Ni/SiO2 (15/85). Transmission electron microscopy of the sol-gel prepared NPs yielded a log-normal distribution with diameter D=3.8(0.2) nm whereas x-ray diffraction data yielded D≃3.3 nm. The TB versus fm variation for fm=0.1–1000 Hz fits the equation TB=Ta/ln(f0/fm) with f0=2.6×109 Hz and Ta=270 K whereas TB versus H data follows the equation TB(H)=33(1-H/H0)m with H0=3200 Oe and m=2(3/2) for lower (higher) H. These results are compared with the predictions of the Néel-Brown model of magnetic relaxation in noninteracting NPs. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

Magnetic properties of nanorods of NiO (diameter ≈5 nm and average aspect ratio ≈12), with and without oleic acid coating, are reported. Temperature variations (5 to 300 K) of the magnetization and electron magnetic resonance (EMR) spectra were measured to determine the respective blocking temperatures Tb(m) and Tb(EMR). The following differences are noted: (1) Tb(m) is reduced from 230 K suncoatedd to 85 K scoatedd for H=25 Oe (2.5 mT); (2d) Decrease of Tb(m) with H is weaker and the ratio Tb(EMR) /Tb(m) is smaller for the uncoated particles. These differences are due to stronger interparticle interaction present in the uncoated particles. [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]

In magnetic nanoparticles (NPs), the observed increase in the effective magnetic anisotropy Keff with the decrease in particle size D is often interpreted, sometimes unsuccessfully, using the equation Keff=Kb+(6KS/D), where Kb is the bulk-like anisotropy of the core spins and KS is the anisotropy of spins in the surface layer. Here, we test the validity of this relation in c-Fe2O3 NPs for sizes D from 15 nm to 2.5 nm. The samples include oleic acid-coated NPs with D=2.5, 3.4, 6.3, and 7.0 nm investigated here, with results on 14 other sizes taken from literature. Keff is determined from the analysis of the frequency dependence of the blocking temperature TB after considering the effects of interparticle interactions on TB. For the c-Fe2O3 NPs with D<5 nm, an unusual enhancement of Keff with decreasing D, well above the magnitudes predicted by the above equation, is observed. Instead the variation of Keff vs. D is best described by an extension of the above equation by including Ksh term from spins in a shell of thickness d. Based on this core-shell-surface layer model, the data are fit to the equation Keff=Kb+(6SS/D)+Ksh{[1-(2d/D)]-3-1} with Kb=1.9x105 ergs/cm3, KS=0.035 ergs/cm2, and Ksh = 1.057x104 ergs/cm3 as the contribution of spins in the shell of thickness d=1.1 nm. Significance of this result is discussed. [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.

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.

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.

Anisotropic diamagnetism of pristine graphite and graphene is well known. Here, evidence of significant induced ferromagnetism in multilayer graphene (MLG) decorated with ferrimagnetic Fe3O4 particles is reported. This MLG-Fe3O4 nano-composite was prepared by a one-step ultrasonic treatment at 75 ℃ in the surfactant sodium dodecyl-benzene-sulfonate. To verify the phase structure and morphology of the composite, X-ray diffraction, scanning and transmission electron microscopy, scanning tunneling electron microscopy, and Raman spectroscopy were employed. Room temperature data of magnetization versus magnetic field showed that the saturation magnetization MS=58.6 emu/gm for pristine Fe3O4 increased to MS=158.4 emu/gm for a 1:1 composite of Fe3O4 to MLG. These results lead to induced MS=253 emu/gm in MLG resulting from its proximity to Fe3O4. Similar experiments on Fe3O4 to single walled carbon nanotubes (SWNT) composite did not show any induced magnetism in SWNT. [ABSTRACT FROM AUTHOR]

A correction to the article "Co-existence of ferrimagnetism and spin-glass state in the spinel Co2SnO4" that was published in the 2013 issue is presented.

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]

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]

In gold nanoparticles (Au NPs) capped with dodecanethiol (DT), the authors report the observation of superparamagnetic blocking temperature TB≃50 K in D≃5 nm NPs but only diamagnetism in 12 nm NPs. For TB=50 K, the strong temperature dependence of coercivity Hc, saturation magnetization Ms, and exchange bias He (in the field-cooled sample) confirm the blocked state resembling ferromagnetism with Hc≃250 Oe, He≃-40 Oe, and Ms≃10-2 emu/g at 5 K. The observed electron magnetic resonance line shows expected shift, broadening, and reduced intensity below TB. A magnetic moment μ≃0.006μB per Au atom attached to DT is determined using a model which yields Ms varying as 1/D, with its source being holes in the 5d band of Au produced by charge transfer from Au to S atoms in DT [ABSTRACT FROM AUTHOR]

The authors report on carbon-assisted water electrolysis at 300 K which only consumes 9.6 kcal/mol H2O (compared to 56.7 kcal/mol H2O for ordinary electrolysis) using the net reaction C(s)+2H2O(ℓ)→CO2(g)+2H2(g). Carbon-assisted H2 production and its kinetics/energetics are measured at applied potential |E0| between 0.1 and 1.8 V (compared to |E0| >1.25 V required for water electrolysis). Surprisingly, H2 produced per W h is higher at the lower voltages, but longer times are required to produce the same amount of H2 The suggested practical conditions are |E0|≃0.5 V and carbon concentration of 0.08 g/cm3. [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]

With the discovery of magnetic ordering in RbMnF3, this unique antiferromagnetic system was recognized as a prime case for a test of conventional spin-wave theory (CSWT) because of its negligibly small anisotropy and its simple, cubic structure. CSWT predicts a simple T2 power-law fall-off of the sublattice magnetization. Yet to this day, no stringent tests have been made of this prediction. Seiden [(Phys. Lett. 28 A, 239 (1968)] deduced a T3 low-temperature behavior on the basis of antiferromagnetic resonance measurements, concluding that CSWT was not supported. We have recently carried out neutron scattering measurements of both single-crystal and powdered samples of RbMnF3 in order to test for CSWT, Seiden's result, and two other more recent semiempirical spin-wave schemes, and we present an analysis of the results. Measurements in the critical regime gave values of the critical exponent β and of TN that are in agreement with previous measurements. [ABSTRACT FROM AUTHOR]

Co-doped TiO[SUB2] (anatase) films prepared by spray pyrolysis at 500°C are investigated for the possible existence of room temperature ferromagnetism (RTF). These films were characterized by x-ray diffraction, Raman spectroscopy, and x-ray photoelectron spectroscopy at room temperature, followed by studies of the temperature and magnetic field dependence of the magnetization by squid magnetometry. For Co doping of upto 10 at. %, no phase other than anatase could be detected, and there is no RTF in these films. Instead, the magnetic susceptibility χ fits the modified Curie-Weiss law χ=χ[SUB0]+C/(T+θ), with θ≃5 K and magnitude of C consistent with Co[SUP2+] paramagnetism in Ti[SUB1-x]Co[SUBx]O[SUB2-x]. Only for T≤5 K, a hysteresis loop with coercivity H[SUBc]=200 Oe is observed. These observations suggest Co[SUP2+] paramagnetism, with exchange interaction becoming important for T ≤5 K in the case of 10% Co/TiO[SUB2] films. [ABSTRACT FROM AUTHOR]

Temperature dependence (5 K to 300 K) of the magnetic properties of two Fe/SiO2 (15/85) nanocomposites with Fe particle size D ≃ 17 nm and 30 nm is reported using magnetometry and electron magnetic resonance (EMR) spectroscopy. Structural characterization of the samples, done by X-ray diffraction, TEM, and Mössbauer spectroscopy shows the presence of α-Fe, amorphous SiO2, and some nanosize Fe3+ oxides. Both samples are ferromagnets in the 5 K to 370 K range with coercivity HC(30 nm) > HC(17 nm). In EMR studies, a single resonance line near g = 2.2 characteristic of α-Fe is observed in both samples at 300 K, with linewidth ΔH(30 nm) > ΔH(17 nm). With decreasing temperature, the EMR line shifts to lower fields and broadens, which is similar to observations in other nanoparticle systems. [ABSTRACT FROM AUTHOR]

Presents an abstract of the study 'Evidence of Clustering of Magnetic Ions in Weakly Doped MgO Crystals,' by M.S. Seehra and J.C. Dean.