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At least 937 records · Page 52Linked to original sources
PubMed1977

Surface, catalytic, and magnetic properties of small iron particles: The effect of chemisorption of hydrogen on magnetic anisotropy.

The superparamagnetic behavior of very small particles of metallic iron (ca 1.5 nm), with about half of their atoms at the surface, is changed reversibly by adsorption and desorption of hydrogen below the superparamagnetic transition temperature. The change after adsorption implies a lowering of the anisotropy energy barrier for the magnetic relaxation of iron and is ascribed to a change in crystalline shape. No such changes are observed for larger particles of iron (ca 8 nm) with about 10% of their atoms at the surface.

Journal Article↗
PubMed2001

Magnetic spin ladder (C5H12N)2CuBr4: high-field magnetization and scaling near quantum criticality.

The magnetization, M(H< or =30 T,0.7< or =T< or =300 K), of (C5H12N)2CuBr4 has been used to identify this system as an S = 1/2 Heisenberg two-leg ladder in the strong-coupling limit, J( perpendicular) = 13.3 K and J( parallel) = 3.8 K, with H(c1) = 6.6 T and H(c2) = 14.6 T. An inflection point in M(H,T = 0.7 K) at half saturation, M(s)/2, is described by an effective XXZ chain. The data exhibit universal scaling behavior in the vicinity of H(c1) and H(c2), indicating that the system is near a quantum critical point.

Journal Article↗
PubMed2002

Quantitative study of magnetization reversal by spin-polarized current in magnetic multilayer nanopillars.

We have studied magnetic switching by spin-polarized currents and also the magnetoresistance in sub-100-nm-diam thin-film Co/Cu/Co nanostructures, with the current flowing perpendicular to the plane of the films. By independently varying the thickness of all three layers and measuring the change of the switching currents, we test the theoretical models for spin-transfer switching. In addition, the changes in the switching current and magnetoresistance as a function of the Cu layer thickness give two independent measurements of the room-temperature spin-diffusion length in Cu.

Journal Article↗
PubMed2004

Controlled normal and inverse current-induced magnetization switching and magnetoresistance in magnetic nanopillars.

By combining pairs of ferromagnetic metals with the same or different signs of scattering anisotropies in ferromagnetic-nonmagnetic-ferromagnetic metal nanopillars, we independently invert just the magnetoresistance, just the direction of current-induced magnetization switching, or both together, at room temperature (295 K) and at 4.2 K. In all cases studied, the switching direction is correctly predicted from the net scattering anisotropy of the fixed ferromagnet, including both bulk and interfacial contributions.

Journal Article↗
PubMed2005

Magnetic form factor of alpha-Ce: towards understanding the magnetism of cerium.

A favored interpretation of the gamma <--> alpha phase transition in cerium postulates the transformation of the localized 4f state in gamma-Ce to a weakly correlated itinerant 4f band in alpha-Ce. However, results of high-energy neutron inelastic scattering measurements, presented here, show clearly that the magnetic susceptibility response from alpha-Ce follows the Ce3+ form factor despite the large, 30-fold, increase in its spectral width relative to that in gamma-Ce. This observation provides, for the first time, indisputable evidence for the localized character of the 4f state in the alpha phase. The present findings appear consistent with recent calculations combining dynamical mean-field theory with the local density approximation that indicate a strongly correlated 4f state in alpha-Ce. The localized 4f state is also fundamental to the Kondo volume collapse theories for the gamma <--> alpha phase transition in cerium.

Journal Article↗
PubMed2001

Magnetic X-ray circular dichroism on in situ grown 3d magnetic thin films on surfaces.

Epitaxic thin and ultrathin films on surfaces allow crystallographic phases that do not occur naturally in the bulk to be stabilized. They also offer new possibilities for an improved understanding of soft X-ray photoabsorption in magnetic systems. Data collected using the Elliptically Polarizing Undulator at BL 5.2 of the Stanford Synchrotron Radiation Laboratory are presented herein. Fe, Co and Ni films were prepared on Cu(100) surfaces. L2,3-edge spectra were recorded with circular and linear light. Fresnel diffractometry was used to quantify the degree of transverse beam coherence. A quantitative analysis of the spectral features indicates a correlation of the spectral intensities and the transverse beam coherence. Resonant reflectivity spectra for Co ultrathin films that exhibit strong dichroism are presented. The reflectivity data indicate that interference effects of the reflected beams at the two interfaces are of importance, even for ultrathin films.

Journal Article↗
PubMedDate not supplied

[Molecular mechanisms of the biological effects of weak magnetic fields. V. Inactivation in vitro of recombinant Rous sarcoma virus reverse transcriptase under the combined action of weak direct and low-frequency alternating magnetic fields, adjusted to the cyclotron resonance of polar amino acid ions].

The effect of weak direct and alternative magnetic fields adjusted to cyclotron frequencies of ions of polar amino acids leads to a functional inactivation of the recombinant reverse transcriptase of Rous sarcoma virus, which is coupled with the proteolysis of this enzyme.

Amino Acids↗
PubMed2004

[Superposition of noise magnetic fields inhibits clustering of fibroblast membrane surface receptors induced by 50 Hz magnetic fields in Chinese hamster lungs].

OBJECTIVE: To study the possible induction effect of exposure to 50 Hz magnetic field (MF) on clustering of cell membrane surface receptors for epidermal growth factor (EGF) and tumor necrosis factor (TNF), the starting site of signals of biological effects, and its possible intervention effect. METHODS: Lung fibroblasts of Chinese hamster (CHL) were exposed to EGF, TNF, 0.4 mT 50 Hz MF, 0.4 mT noise MF, and 0.4 mT 50 Hz MF combined with 0.4 mT noise MF. Respectively, for different durations, following the treatment, EGF and TNF receptors on the cell membrane were marked by corresponding antibodies with immunohistochemical method, then observed under a confocal microscope. RESULTS: Clustering of cell membrane receptors could be induced 5 min after treatment with EGF and TNF, as well as with 50 Hz MF at 0.4 mT, which reached the peak in 15 min. While noise MF with the same intensity did not induce clustering of cell membrane receptors. Superposition of noise MF with the same intensity could inhibit clustering of cell membrane receptors induced by 50 Hz MF. CONCLUSION: Clustering of EGF and TNF receptors on the cell membrane could be induced by 50 Hz MF, suggesting that membrane receptors would be one of the sites where MF signals coupled, and noise MF with the same intensity could inhibit these effects.

Animals↗
PubMedDate not supplied

[Molecular mechanisms of biological action of low magnetic fields. IV. Proteolysis of protein-DNAse 1 inhibitor in water phase under combined action of low constant and alternating magnetic fields adjusted to cyclotron resonance of polar amino acid ions].

It was shown that combined action of weak magnetic fields adjusted to cyclotronic frequencies of polar amino acids ions, on aqueous solutions of acidic non-histone protein-inhibitor of DNAase 1 led to proteolysis of this inhibitor. The fragments obtained as a result of proteolysis differ from the whole molecule by amino acid composition and the time of elution from column in case of HPLC.

Animals↗
PubMed1999

Experimentally verified, theoretical design of dual-tuned, low-pass birdcage radiofrequency resonators for magnetic resonance imaging and magnetic resonance spectroscopy of human brain at 3.0 Tesla.

A new theoretical method is presented for designing frequency responses of double-tuned, low-pass birdcage coils. This method is based on Kirchhoff's equations through a nonsymmetric matrix algorithm and extended through a modification of the corresponding eigenvalue system from a single-tuned mode. Designs from this method are verified for sodium/proton, dual-tuned, double-quadrature, low-pass birdcage coils at 1.5 Tesla and 3.0 Tesla and then are used to design dual-tuned, double-quadrature, lithium/proton and phosphorus/proton birdcage coils for 3.0 Tesla. All frequencies show experimental deviations of less than 3% from theory under unloaded conditions. The frequency shifts caused by loading and radiofrequency shielding are less than 1 MHz and can be compensated readily by adjustment of variable capacitors. Applications to human neuroimaging and spectroscopy are demonstrated.

Brain↗