Field induced magnetic density in the paramagnetic compound LuCo2

The magnetization density induced in LuCo₂ by an applied magnetic field was measured by means of polarized neutron diffraction. The measurements were performed on a single crystal at 100 K in an applied field of 57.2 kOe. The observed density is localized on Co atoms with a form factor which is, within the experimental accuracy, similar to that of 3d electrons in Co metal. Weak additional magnetic amplitudes reveal a nonuniform polarization of the conduction band. Its mean value is opposite to the Co moment as in Co metal.     

Electrodeposition and characterization of Cu/Co multilayers: Effect of individual Co and Cu layers on GMR magnitude and behavior

The present work discusses the successful electrodeposition of Cu/Co multilayers, exhibiting appreciable GMR of 12-14% at room temperature. The effect of individual Cu and Co layers on the magnitude and behavior of GMR has been studied. By varying the thickness of individual layers the field at which saturation in GMR is observed can be controlled. It was observed that for lower thicknesses of Co layer, the saturation fields are reduced below 1 kOe. The Cu layer thickness seems to control the nature of magnetic coupling and the saturation field, with the two showing a correlation.     

Giant injection magnetoresistance in gallium arsenide/granulated film heterostructures with nanosize cobalt inclusions

Electron transport has been studied in the gallium arsenide/granulated SiO₂ film heterostructure with Co nanoparticles and in the gallium arsenide/TiO₂ film heterostructure with Co island sublayers. When electrons are injected from a film into a semiconductor, a new phenomenon is observed, which is called injection magnetoresistance. For the SiO₂(Co)/GaAs structure with 60 at. % Co in a magnetic field of 23 kOe at a voltage of 50 V, the injection magnetoresistance reaches 5200% at room temperature.     

Nuclear orientation of60Co in concentrated CoAu alloys

We report β-particle and γ-ray angular distribution measurements from⁶⁰Co oriented in CoAu at low temperatures in applied fields up to 72 kOe and Co concentrations of 0.95 to 11 at.%. The results are explained by assuming a random molecular field interaction between groups of Co impurities. The hyperfine field on Co nuclei in groups of three or more nearest neighbors is negative and has a value near ?180 kOe. The induced field on Co-pair nuclei is small and probably also negative. Complete polarization of the Co moments in the more concentrated alloys requires a very large applied field.     

Electrical relaxation induced by magnetostriction in a MEMS device

Electrical resistance relaxation measurements were performed on a regular array of Co magnetic antidots submitted to a magnetic field, using a thin Cu film with bone-like shape positioned across the pattern; the introduction of a thin resist layer spin-coated on the Cu bridge before the deposition of the external leads introduced a hopping-dominated path for injected currents, controlled by the barrier thickness. The in-plane magnetic field generated by an electromagnet was switched between 0 and 3.5 kOe (fully saturated Co) and kept constant while the resistance was continuously monitored under steady current injection. A strong, unsaturating resistance variation with time after field switching was measured, corresponding to a resistance decrease greater than 20% after tents of ks. When the field was switched from 3.5 kOe back to zero the measured resistance displayed a corresponding positive variation. The two effects were repeatedly observed by subsequently cycling the magnetic field. Electron microscopy analysis showed that a peculiar dendritic structure had developed in the polymeric resist, consisting of mass density oscillations whose principal arms were oriented roughly at 45° with respect to the current density vector, possibly because of the mechanical stress induced by magnetostriction of Co antidots. A detailed analysis showed that mass density fluctuations within dendritic structures may be correlated with specific perturbation events observed in the electrical resistance relaxation during the measurements.     

Co/Cu multilayers studied by using the119Sn probe

To observe spin polarization in nonmagnetic layers sandwiched by magnetic layers,¹¹⁹Sn Mössbauer spectra of [Co(20 Å)/Cu(20-x Å)/¹¹⁹Sn(1.5 Å)/Cu(x Å)] (x=0, 5 and 10) multilayers were measured. A magnetic fraction is observed in every spectrum, and the average hyperfine field ¯H _f at Sn nuclei in a Cu layer changes from 14 kOe (x=0) to 8 kOe (x=10). It was also observed that the polarization is greatly reduced by adding a Cr layer of only 2 Å to the Co/Cu interfaces. The spectrum of thex=10 film, measured under an external field of 30 kOe, cannot be interpreted without assuming magnetic fractions both in parallel and antiparallel to the external field, which indicates an oscillation of spin polarization in a Cu layer.     

Crystallization and magnetic properties of melt-spun neodymium-iron alloys

The magnetic and crystallization properties of melt-spun Nd_1?xFe_x alloys are reported. By using high purity constituents and an extremely fine orifice (100–150 μm), amorphous alloys were prepared over the interval 0.4 ? x ? 0.8. Their magnetic properties, taken between 20–850 K in fields up to 95 kOe, are interpreted on the basis of a sperimagnetic structure; at high field the alloys from collinear ferromagnetic structures. Room temperature coercivities of the amorphous alloys are relatively low (1.5–2.0 kOe) but increase substantially at reduced temperatures; at 20 K, a maximum coercivity of 52 kOe was found for a Nd_0.4Fe_0.6 alloy. X-ray diffraction indicates that the melt-spun alloys crystallize by the precipitation of Nd metal and an unidentified Nd-Fe phase. Changes in magnetization and coercivity during crystallization are reported.     

Effects of magnetic field on shape evolution of Fe–Co particles in a Cu matrix

The effects of magnetic field on the shape evolution of ferromagnetic fcc Fe–Co particles in Cu–0.83 at.% Fe–1.37 at.% Co alloy single crystals were examined using magnetic anisotropy measurements. The Cu–Fe–Co single crystals were aged at 993 K for 2 h to 24 h under a magnetic field of 10 T parallel to either the [001] or [011] direction. The magnetic anisotropy was examined by measuring magnetic torque around the (100) plane. It was found that the fcc Fe–Co particles are elongated in the direction parallel to the magnetic field. Furthermore, the elongation along [001] is more remarkable than that along [011]. The results are explained quantitatively by considering the minimization of the sum of the interface energy, elastic strain energy and magnetostatic energy of spheroidal particles.     

Electron scattering with spin flip in indium antimonide and indium arsenide

The longitudinal magnetoresistance has been investigated at temperatures in the range from 2.8 to 200 K in a magnetic field of up to 200 kOe with the aim of determining the temperature range and the magnetic field strength at which charge carrier scattering with spin flip occurs in n-type indium arsenide and n-type indium antimonide. It is established that quantum oscillations of the longitudinal magnetoresistance of indium arsenide exhibit weak zero maxima due to electron scattering with spin flip at temperatures in the range from 4 to 35 K in a magnetic field of 146 kOe. For the longitudinal magnetoresistance of indium antimonide, zero maxima caused by electron scattering with spin flip are revealed in the temperature range from 60 to 80 K in a magnetic field of 132 kOe.     

Absence of intrinsic ferromagnetic interactions of isolated and paired Co dopant atoms in Zn1-xCoxO with high structural perfection

We report element specific structural and magnetic investigations on Zn(1-x)Co(x)O epitaxial films using synchrotron radiation. Co dopants exclusively occupy Zn sites as revealed by x-ray linear dichroism having an unprecedented degree of structural perfection. Comparative magnetic field dependent measurements by x-ray magnetic circular dichroism and conventional magnetometry consistently show purely paramagnetic behavior for isolated Co dopant atoms with a magnetic moment of 4.8 (mu B). However, the total magnetization is reduced by approximately 30%, demonstrating that Co-O-Co pairs are antiferromagnetically coupled. We find no sign of intrinsic ferromagnetic interactions for isolated or paired Co dopant atoms in Co:ZnO films.     

Evolution of modulated structure in Fe–Cr–Co alloy during isothermal ageing with different external magnetic field conditions

The evolution of modulated structure in Fe–Cr–Co alloy during isothermal ageing with and without external magnetic field was investigated by using transmission electron microscopy (TEM) and phase-field simulation. The isotropic modulated structure in Fe–Cr–Co alloy formed during isothermal ageing without external magnetic field could be converted to be anisotropy during further isothermal ageing under an 8 kOe external magnetic (thermo-magnetic treatment), and the formation of anisotropy was slower than the direct formation from spinodal decomposition under external magnetic field and is time dependent. The anisotropy characteristic of modulated structure in Fe–Cr–Co alloy subjected to thermo-magnetic treatment for 1 h remained during further isothermal ageing without external magnetic field for up to 20 h. Novel modulated structure could be obtained through specific thermo-magnetic treatment processes, which was confirmed by phase-field simulation.     

Change in the Magnetocapacity in the Paramagnetic Region in a Cation-Substituted Manganese Selenide

The capacity and the dielectric loss tangent of a Gd _x Mn_1–xSe (x ≤ 0.2) solid solution have been measured in the frequency range 1–300 kHz without a magnetic field and in a magnetic field of 8 kOe in the temperature range 100–450 K, and the magnetic moment of the solid solution has been measured in a field of 8.6 kOe. The magnetocapacity effect and the change in the magnetocapacity sign have been observed in room temperature in the paramagnetic region. A correlation of the changes in the dielectric permittivity and the magnetic susceptibility with temperature has been revealed. The magnetocapacity is described using the model with orbital electron ordering and the Maxwell–Wagner model.     

Magnetic hysteresis in rapidly quenched rare-earth alloys

The magnetic and structural properties of rapidly quenched (Pr₈₀Ga₂₀)_100-xFe_x, RTbFe and RTbFe(Co)M alloys are examined over a wide range of chemical compositions, where R ≡ Pr, Sm, MM and M ≡ B and Si. The Ga-containing samples show relatively high coercive fields (up to 3 kOe) in the amorphous state which subsequently disappear after crystallization. On the other hand, the high coercive fields (≈5 kOe) of melt-spun RTbFe samples decrease slightly after crystallization but their magnetic moment increases substantially. Melt-spun RTbFe(Co)M samples are generally magnetically soft in the as-quenched state. Magnetic hardening is produced by annealing the samples around 750°C leading to coercive fields which could not be measured with an ordinary electromagnet (H_c #62; 23 kOe). The best properties have been obtained on a Pr₁₄Fe₇₁B₁₅ sample with a coercive field of 8 kOe and an energy product of 8.5 MGOe. Thermomagnetic data show that a structural transformation takes place upon heating the samples to 750°C. The Curie temperature of the precipitate phase is around 320°C while that of the as-quenched phase is around 160°C. Transmission electron microscope studies show a very fine precipitate structure with a precipitate size below 100 Å. The precipitate phase is believed to be highly anisotropic leading to the observed hard magnetic properties.     

Anisotropy of the Hall Effect in the Paramagnetic Phase of Ho0.8Lu0.2B12 Cage Glass

JETP Letters - Detailed measurements of the Hall effect in the paramagnetic phase of Ho0.8Lu0.2B12 antiferromagnet at the magnetic field up to 80 kOe in the temperature range of 1.9–300 K...     

Colossal Magnetoresistance of Layered Manganite La<Subscript>1.2</Subscript>Sr<Subscript>1.8</Subscript>Mn<Subscript>2</Subscript>O<Subscript>7</Subscript> and Its Description by a “Spin–Polaron” Conduction Mechanism

The resistance of a La_1.2Sr_1.8Mn_2(1–z)O₇ single crystal has been studied in magnetic fields from 0 to 90 kOe. The magnetoresistance at temperature T = 75 K, near which a colossal magnetoresistance maximum is observed, has been successfully described in terms of the “spin–polaron” electric conduction mechanism. This value of the colossal magnetoresistance is due to a three-fold increase in the polaron size. The method of separating contributions of various conduction mechanisms to the magnetoresistance developed for materials with activation type of conduction is generalized to compounds in which a metal–insulator transition is observed. It is found that, at a temperature of 75 K, the contribution of the “orientation” mechanism is maximum (≈20%) in a magnetic field of 5 kOe and almost disappears in fields higher than 50 kOe.     

Effect of field cooling on magnetic properties of ultrafine CoO/Co particles

In CoO-Ag granular films with small CoO contents, we have observed ultrafine Co particles inside or on the surface of the CoO particles. After field cooling under the external magnetic field of 50 kOe, a sustained magnetization (or vertical) shift and exchange field shift were observed. The magnetization shift and the exchange field shift increased as the cooling field is increased and temperature decreased, in correlation to each other. PACS 75.30.Et; 75.30.Gw; 75.75.+a     

Magnetoelectric Effect in a Paramagnetic Region in Gd0.15Mn0.85Se

Physics of the Solid State - The electric polarization in a zero magnetic field and in a magnetic field of 12 kOe is measured in a GdxMn1&nbsp;–&nbsp;xSe solid solution in the...     

A Mössbauer study of iron and iron–cobalt nanotubes in polymer ion-track membranes

Iron and iron–cobalt nanostructures that were synthesized in polymer ion-track membranes have been studied via Mössbauer spectroscopy combined with raster electron microscopy, energy-dispersion analysis, and X-ray diffraction data. The obtained nanostructures are single-phase bcc Fe_1–xCo_x nanotubes with a high degree of polycrystallinity, whose length is 12 μm; their diameter is 110 ± 3 nm and the wall thickness is 21 ± 2 nm. Fe²⁺ and Fe³⁺ cations were detected in the nanotubes, which belong to iron salts that were used and formed in the electrochemical deposition. The Fe nanotubes exhibit eventual magnetic moment direction distributions of Fe atoms, whereas Fe/Co nanotubes have a partial magnetic structure along the nanotube axis with a mean value of the angle between the magnetic moment and nanotube axis of 34° ± 2°. Substituting the Fe atom with Co in the nearest environment of the Fe atom within the Fe/Co structure of nanotubes leads to a noticeable increase in the hyperfine magnetic field at the ⁵⁷Fe nuclei (by 8.7 ± 0.4 kOe) and to a slight decrease in the shift of the Mössbauer line (by 0.005 ± 0.004 mm/s).     

Size effect of the longitudinal magnetoresistance of thin films of n- type Ge

In a study of the longitudinal magnetoresistance as a function of the magnetic field in samples of n-type Ge of various thicknesses at 300°K and 77°K, the surface of the samples was oriented parallel to the (001) plane. The directions of the current and the magnetic field were along either the <100> direction or the <110> direction. As the thickness of the samples was reduced, regardless of the orientation of the current and the magnetic field with respect to the crystallographic directions, a decrease was observed in the magnetoresistance over the entire range of magnetic fields studied, 1–280 kOe. The experimental results are attributed to a screening-length size effect and to “sliding” orbits in the enriched surface layers, which lead to an increase in the electron mobility in a strong magnetic field.     

Ultralow-frequency magnetoelectric effect in a multilayer ferrite-piezoelectric structure

The magnetoelectric effect is experimentally studied in a multilayer nickel zinc ferrite-lead zirconate titanate structure at frequencies of 10^?3–10 Hz that is placed in a harmonically modulated magnetic field of amplitude to 1 kOe. The nonlinearity of the ferrite magnetostriction and the conductivity of the films are shown to double the frequency and distort the shape of the magnetoelectric voltage. The magnetoelectric signal amplitude decreases linearly with decreasing field modulation frequency. The feasibility of using the magnetoelectric effect to detect ultralow-frequency magnetic fields is demonstrated.