Magnetocrystalline anisotropy nickel - vanadium alloys

Single crystals of 5N and 4N pure Ni and a series of NiV alloys up to 6.72 at % V were grown and cut into spheres and blocks for anisotropy, magnetization and resistivity measurements. Measurements of the first anisotropy constant of these crystals were made between 4.2 and 300K using a torque magnetometer. All the measurements were performed when the magnetic field of up to 11 k0e could rotate in a (001) plane. Corrections for the effect of the higher order constant K(_3) on the torque curves were found to be necessary in the case of pure Ni and 0.98% alloy. Using a Faraday balance the magnetizations of the crystals of higher vanadium content were measured from 77K to room temperature. Values of M at 4.2K were measured to check the validity of the extrapolation of these results to OK. Using a D.C. method it was possible to measure the values of the resistivity of these samples from 4.2K to room temperature. In addition crystals of Ni Mo with 1 at % Mo and of NiV with 12.5 at % V were grown and their resistivities were measured from 4.2K to room temperature. Using the results from anisotropy measurements it was possible to show that variations of temperature or of concentration affect the first anisotropy constant in a similar manner. This is in good agreement with the results on Ni Mo of Hausmann and Wolf (1971). The results from anisotropy and resistivity measurements were combined to check whether the hypothesis suggested by Hausmann (1970) were true. This was found not to be so even though the relationship was examined for a wide range of temperature. Combining the results of anisotropy and resistivity measurements it has been found that there is further support for the suggestion by Franse et al. (1973) of a link between temperature variation of anisotropy and the minority spin resistivity in accord with the work of Furey. There remains some doubt about the correctness of the method of distinguishing between majority and minority spin resistivities. The temperature variation of K(_1) and M was also examined and the value of n found in equation K(T,C) = K(O,C) [ M(T)/M(O) ](^n) in the case of NiV crystals is less than that for pure Ni and it decreases as the concentration is increased

Ac-Susceptibility of Granular Superconductors

The real and imaginary parts of ac-susceptibility of sintered Y Ba2 CU3 Ox and (BiJ.6 PbO.2 SbO.2) Sr2 Ca2 CU3 Ox superconductors were measured before and after powdering. The temperature-dependent susceptibility may be separated into two contributions, one sensitive and the other relatively insensitive to the magnitude of the measuring field. The former is partially suppressed by coarsely crushing the sample. It is completely suppressed after finely powdering. Some of the models apparently consistent with the results are discussed

Magnetic studies of Bi x Y3-x Fe5O12 fabricated using conventional method

A series of Bi substituted yttrium iron garnet (Bi-YIG) nanoparticles with nominal formula of BixY3 − xFe5O12 in which x varied in steps of 0.0, 0.25 and 0.5 are prepared by conventional method. Vibration sample magnetometer (VSM) at Room temperature (RT) shows saturation magnetization decreases from 27.4 to 25.2 (emu/g) as x value increases from 0.0 to 0.5. Room temperature 57Fe Mössbauer spectra are recorded for these series. The hyperfine field value for octahedral and tetrahedral of samples increases from 484 and 390 kOe to 491 and 397 kOe respectability, as Bi replaces Y in (BixY3 − xFe5O12) atom with increasing x value. The effect of Bi3 +  substitution for Y3 +  on lattice constants, morphology and magnetic properties of pure YIG has been investigated

Preparation and Characterization of Manganese FerriteNanoparticles via Co-precipitation Method forHyperthermia: Mn ferrite nanoparticles preparation

In this work, Mn ferrite nanopowders were prepared by co-precipitation method and were characterized. Phase identification of the nanopowders was performed by X-ray diffraction method and the mean particle size of the nanopowders was calculated by Scherrer's formula, using necessary corrections. Magnetic parameters of the prepared nanopowders were measured by a vibrating sample magnetometer .Asensitive thermometer was used to measure the increase in temperature due to application of an alternating magnetic field on suspended magnetic nanopowders in water. Transmission electron microscope investigations showed that the particle size distribution was homogeneous and their size was in a good agreement with those obtained by Scherrer's formula. The results show that a single phase Mn ferrite can be obtained by co-precipitation method at 70 °C with a mean particle size of 5 nm and a 5 °C temperature increase is achievable in an AC magnetic field

The correlation of lattice constant with superexchange interaction in Bi-YIG fabricated by mechanochemical processing

Magnetic and structural properties of Bi substituted YIG with nominal formula of Bi x Y3 − x Fe5O12 (x = 0.0, 0.25, 0.5, 0.75, 1.00) prepared via Mechanochemical Processing (MCP) have been studied with Mossbauer spectroscopy, X-ray diffraction (XRD). The temperature dependence of sublattice magnetic hyperfine field for samples is analyzed. The a–d intersublattice superexchange found to be antiferromagnetic and increases from − 21.97 to − 25.79 kB as Bi increases from 0.0 to 0.25. The a–a and d–d intrasublattice exchanges for sample x = 0.0 are 13.18 and 10.55 kB respectively while for sample x = 0.25 a–a and d–d intrasublattice exchanges are 7.7 and 8.9 kB respectively. The correlation of lattice constant and superexchange interaction are discussed

Anisotropy and interface structure in sputtered Co/Pt multilayers on Si

The inter-relation between magnetic and structural properties of a series of Co/Pt sputtered multilayer films of constant period but differing number of repeats has been investigated. Independent measurements of the perpendicular anisotropy using vibrating sample, alternating gradient field and torque magnetometry were in excellent agreement. Previous measurements showing a large increase in effective anisotropy at about 15 bilayers were confirmed. Low and high angle X-ray scattering showed that the roughness of the interfaces was correlated in all samples and that the interfaces were sharp with no detectable interdiffusion. No systematic trends in roughness, in-plane correlation length or crystallographic texture could be detected with increasing bilayer repeat. The samples with higher perpendicular anisotropy had both lower Co and Pt thickness than the other samples, although this enhancement does not seem to be associated with the thickness variation. The interfaces in these samples had a fractal parameter h of unity, compared with 0.5 for the other samples