Cobalt magnetization curves

The Akulov law corresponds magnetization saturation for polycrystals and nanoparticles without exchange interaction between them. In the system of exchange coupled particles the magnetization curve is described by another power low. Thus, the relation M observed in the experiment is indicative of the lack of exchange interaction between the cobalt nanoparticles. 

Fig. 54 Magnetization curve for easy [0001 — c axis] and hard [1010] axis for cobalt showing large magnetocrystalline anisotropy (from Ref. 122).

Fig.l. The influence of 7 layers of barium stearate (curve b) in reducing the frictional coefficient between a cobalt magnetic tape and a recording head. Curve (a) is for an unprotected metal surface. (See Reference 8)... 

Figure 16.8. ZFC-FC magnetization curves of the CoFe204-Si02 nanocomposite aerogel with 5 wt% loading of cobalt ferrite (reproduced from [28] by permission of American Chemical Society).

Figure 20.18 Magnetization curves for single crystals of cobalt. The curves were generated when the magnetic field was applied in [0001] and [1010]/[1120] crystallographic directions.

Fig. 13.30 Isothermal magnetization curves of LiCoo.75Bo.25O2 cathode material. The saturation moment is due to Ni clusters (60 ppm of Ni) that come from the Ni impurities in commercial cobalt oxide (<0.4 %)...

Cobalt magnetic nanocomposites - top curve RDF computed from a spherical model with bulk cobalt hep structure (320 atoms) middle cobalt nanoparticles in polyphenyloxide (PRO), 4.2nm in diameter (from HRTEM) bottom cobalt nanoparticles in polyvinylpyrrolidone (PVP), 1.4nm in diameter for the bigger size, particles are structurally close to bulk metal whereas the very small size induces both a lower symmetry structure (polytetrahedral) and a strong increase of magnetization. ... 

An obvious refinement of the simple theory for cobalt and nickel and their alloys can be made which leads to a significant increase in the calculated value of the Curie temperature. The foregoing calculation for nickel, for example, is based upon the assumption that the uncoupled valence electrons spend equal amounts of time on the nickel atoms with / = 1 and the nickel atoms with J = 0. However, the stabilizing interaction of the spins of the valence electrons and the parallel atomic moments would cause an increase in the wave function for the valence electrons in the neighborhood of the atoms with / = 1 and the parallel orientation. This effect also produces a change in the shape of the curve of saturation magnetization as a function of temperature. The details of this refined theory will be published later. 

JFiq. X-l.—Curves showing the reciprocal of molar magnetic susceptibility of compounds of cobalt(II) as a function of the absolute temperature. 

In a graph of 1/xmoiar against T, the points lie on a straight line if the Weiss equation is valid. Measurements for three salts of cobalt(II) are shown in Figure X-l. It is seen that the curves are straight lines except at very low temperatures. Their slopes are the same the slope is the reciprocal of the Curie constant, and accordingly the cobalt (II) atom has the same magnetic moment in the three substances. 

There has been a considerable effort in the physics and chemistry communities to use INS methods to study magnetic dynamics, which can often be described as spin waves. Measurements of spin wave dispersion curves can provide information about the interactions between atomic magnetic moments, the so-called exchange interactions. There have been comparatively few INS measurements on magnetic minerals. INS methods have been used to produce spin wave dispersion curves for hematite. Crystal field magnetic transitions in cobalt bearing cordierite, and spinel phases have also been studied by INS. ... 

The thermal decompositions of nickel(II)-cobalt(II) oxalate solid solutions were studied using TG and TM [103], A series of the mixed binary Ni(II)-Co(II) oxalate samples was prepared at 25% (atom) intervals across the system. Physical mixtures were also prepared by mixing the pure end members. The DTG and DTM curves showed that the decomposition proceeds to completion in two overlapping stages. The kinetics of the individual steps were not studied. From the DTG curves, the authors stated that the physical mixtures behaved as individual oxalates, while the coprecipitate decomposed as a single entity. The TM curves showed that the products formed from the physical mixture and the coprecipitate were distinctly different. The magnetic behaviour of the product from the coprecipitate was consistent with the behaviour predicted for a Ni-Co alloy, but the products from the physically mixed oxalate do not show the transition temperature predicted for an alloy. The kinetics of decomposition of iron-nickel mixed oxalates have been studied by Doremieux et al. [104]. 

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