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Magnetic properties of Ni3C nanoparticles, about 40 nm in diameter, have been investigated. The sample exhibits weak ferromagnetic (FM), spin-glass (SG), and paramagnetic (PM) properties by alternating current susceptibility and direct current magnetization measurements. The freezing temperature of the SG phase at zero applied field is determined as TF0∼11.0 K. At T>TF0, a very weak ferromagnetism has been observed over a strong PM background. The Curie temperature TC is shown to exceed 300 K, and the ferromagnetism at 300 K is determined as about 0.02 emu/g∼6.7×10-4 μB per Ni3C formula unit. An anomalous dip appears in the temperature dependent coercivity HC(T) near the freezing temperature TF0. It reflects the distortedly reduced coercivity in the M(H) hysteresis loop measured at T∼TF0 with the applied sweeping field approaching H=0. This is attributable to the interaction between the SG and the weak FM phases. The possible origin of the magnetic moments that account for the observed FM, SG, and PM properties is discussed. [ABSTRACT FROM AUTHOR]

A practical approach is theoretically proposed for the formation and manipulation of the chirality of a magnetization flux closure (MFC) state. It is realizable over a circular array consisting of a few single-domained (SD) nanomagnets. The entire array size is smaller than 100 nm. The investigation is performed by numerical calculations based on the Landau–Lifshitz–Gilbert equation. Parameters concerning the formation and stability of the MFC state are obtained for the circular arrays of five and six nanomagnets. The effect of the applied field orientation on the manipulation of the chirality is investigated. In addition, the critical distance LC is determined, beyond which the effect of magnetic coupling between adjacent arrays becomes negligible. The corresponding maximum density of arrays without the magnetic coupling effect is thus estimated. Our work makes the application of the collective MFC state in the ultrahigh density magnetic storage possible, exceeding 200 Gbits/in2. [ABSTRACT FROM AUTHOR]

The finite size effect on the antiferromagnetic transition temperature, TN, has been investigated with Co3O4 nanoparticles of 75, 35, and 16 nm in diameter. Along with the results from the previous experiments on the Co3O4 nanoparticles with average diameter of 8 and 4.3 nm, the variation of TN with the particle diameter, d, appears to follow the finite size scaling relation. The shift exponent is determined as λ=1.1±0.2 and the correlation length ξ0=2.8±0.3 nm. The value of the shift exponent is consistent with the description by the mean field theory. [ABSTRACT FROM AUTHOR]

The magnetization ground states (MGSs) for a nanosized Co hollow sphere, with the outer radius, R<50 nm, have been studied numerically by micromagnetic simulation using object oriented micromagnetic framework (OOMMF). In addition to the originally known single domain and vortex-curling states, a three dimensional “onion” state with a corresponding analytical expression is proposed and confirmed as one of the ground states. Two phase diagrams, one for a single crystalline and the other for a polycrystalline nanosphere, are obtained for the three MGSs. The result reveals that the magnetic anisotropy has a significant effect on the phase line in the diagrams. The finite temperature effect and the blocking properties of the nanosphere for the magnetization reversal are discussed. [ABSTRACT FROM AUTHOR]

The thermoelectric power (TEP) and the electrical resistivity of the intergranular magnetoresistance composite (1-x)La[sub 2/3]Ca[sub 1/3]MnO[sub 3]/(x)yttria-stabilized zirconia (YSZ) (LCMO/YSZ) with x=0%, 0.75%, 1.25%, 4.5%, 13%, 15%, and 80% of YSZ have been measured from 300 down to 77 K. A pronounced TEP peak appears during phase transition for samples with x>0, while it is not observed for x=0. We suggest that this is due to the magnetic structure variation induced by lattice strain which is a result of the LCMO/YSZ boundary layers. The transition width in the temperature derived from dχ/dT, with χ the ac magnetic susceptibility, supports this interpretation. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetoresistance (MR) of a nanostructured material, monodisperse Fe3O4 nanospheres of about 200 nm coated with thin SiO2 and compactly cold pressed and sintered, has been investigated. A high MR, up to 10.8% at 1 T and 17% at 8 T, has been observed at 100 K. This enhanced MR is likely arising from the spin-polarized tunneling of conducting electrons through the insulating SiO2 boundaries. The decrease of the MR with the temperature increasing was attributed to the existence of the local spins in the grain boundaries. In addition, the MR ratio decreases with the SiO2 thickness increasing and sintering temperature decreasing. It suggests that the magnetic property of the insulating barrier is crucial for enhancing the low-field MR at a high temperature. [ABSTRACT FROM AUTHOR]

Using a one-step solution phase approach, the authors have synthesized uniform jingle bell-shaped cobalt mesopheres (550–750 nm) and assembled the mesospheres into long magnetic chains (20–30 μm). All of the cobalt spheres are hollow with ∼40 nm thick shells but each contains an ∼200 nm diameter solid ball. The nano- to mesoscale structures were realized via reaction of CoCl2·6H2O and N2H4·H2O in the presence of polyvinylpyrrolidone (PVP) in an ethylene glycol solution. Magnetic measurements show a coercivity of about 75 Oe with a remnance of 9.6 emu/g at 300 K. We propose a possible mechanism for the formation of the nanoto mesoscale structures. [ABSTRACT FROM AUTHOR]

TbMnO3 thin films with different crystallographic orientations were deposited epitaxially on LaAlO3 [100] and SrTiO3 [100] single crystal substrates by using pulsed laser deposition. Magnetization measurements were performed along the [110], [-110], and [001] directions of the films. Obvious magnetic anisotropy and low temperature ferromagnetism were found. Transitions at T ∼ 10, 32, 120, and 125 K along different directions are observed. The susceptibility anomalies, remarkably anisotropic, are discussed on the frame of the domain wall and strain-induced distortion. Particularly, the lattice mismatch and the anisotropic thermal expansion between the films and substrates are likely responsible for the distortion behaviors. [ABSTRACT FROM AUTHOR]