Cobalt Curie temperature

For alloys of iron, cobalt, nickel, and copper the calculated values of saturation magnetic moments agree closely with the observed values in particular, the maximum value of about 2.48 magnetons at electron number about 26.3 is reproduced by the theory. There is, however, only rough agreement between the observed and calculated values of the Curie temperature. 

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. 

The spinel ferrites were fabricated by solid state reaction technique. Cobalt and Zinc ferrites CoxZnyFe204,(x=0.7,0.3,0.4,0.2 and y=0.3,0.7,0.6,0.8) were prepared by solid state reaction technique. The crystalline structure of the sample was investigated by X-ray diffraction(XRD). All samples show cubic spinel structure. The lattice parameter decreases with increasing cobalt content. Magnetic properties shows that the prepared sample exhibit ferromagnetic behaviour at room temperature. The saturation magnetization increases with increasing cobalt content. Curie temperature... 

By increasing the temperature of a ferromagnetic you can reach a point at which the ferromagnetic character disappears and the material becomes paramagnetic. This is called the Curie temperature. Curie temperatures of some ferromagnetic sustances are iron 770 °C, nickel 358 °C and cobalt 1123 °C. 

Cobalt is a hard, bluish-white metal (mp 1493°C, bp 3100°C). It is ferromagnetic with a Curie temperature of 1121°C. It dissolves slowly in dilute mineral acids, the Co2+/Co potential being -0.227 V, but it is relatively unreactive. While it does not... 

The Fe resonance shows no magnetic hyperfine splitting below the Curie temperature for x = 0 01, 0-25, 0-50, and 0-75. One can therefore conclude that the iron atoms do not participate in the magnetic order, which is consistent with a proposed model of localised 3rf-electrons on the cobalt ions. 

For raising the Curie temperature, Co is added to substitute partially for Fe (Sagawa et al. 1984b). Cobalt, however, reacts with Nd to form a paramagnetic Nd-Co (NdsCo) phase at grain boimdaries, which deteriorates the obtainable maximum flux density. However, the addition of Co does increase the corrosion resistance of the magnets (Fidler et al. 1991, 1994). 

Ohashi et al. (1987) studied the addition of Co to improve the corrosion resistance. As mentioned above, cobalt substitution was also known to increase the Curie temperature. Even though the anisotropy field of materials doped with less than 3 at.% Co is almost constant, the coercivity of the doped magnets decreases drastically (Grossinger et al. 1987). 

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