Nickel 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. 

Figure 6.57 Schematic relationship of outer-sheU energy bands in nickel over the Curie temperature.

It is believed that palladinm may have a distribntion of electrons similar to that of nickel. At room temperatnre the picture for palladium is like Figure 6.57 for Ni above the Curie temperature, except that we now have to deal with a 5s band instead of 4, and 4d instead of 3d. The addition of hydrogen in solntion in metallic palladium reduces the susceptibility. The hydrogen is ionized, with the free electrons joining the palladium bands just as the valence electron of copper joins the bands of nickel. 

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. 

Figure 3.17 Heat-flux DSC trace at 10°C/min of the ferromagnetic to paramagnetic lambda transformation at 354°C in nickel (dotted line). The Curie temperature indicated by the DSC trace is 346°C (dot-dashed line).

Figure 5.6 Calibration of TG thermocouple using the Curie temperatures of ferromagnetic materials [8], Curie temperatures alumel 163°C, nickel 354°C, perkalloy 596°C, iron 780°C, hi sat 50 1000°C. Since Curie temperatures are temperatures at which all ferromagnetism ends (lambda transformation), the extrapolated end-points of weight loss are measured from the trace.

Saturation magnetization and Curie temperatures for nearly equiatomic Pq - Ni alloys compared with unalloyed nickel (Beille et al. 1978). 

Connelly et al. measured the specific heat of pure single-crystalline nickel near the Curie temperature using a calorimetric technique which permits direct observation of C° (T) as a continuous function of T, with a temperature resolution of about 10 K. Special attention has been devoted to the determination of the analytical form of the magnetic contribution to C" (7). 

Figure 16.5 The TGA Curie point method records for each standard an apparent sharp weight change at a well-defined temperature, which corresponds to a known transformation in the standard s ferromagnetic properties at that temperature. The figure shows the relative temperature precision from three replicate calibration runs using alumel and nickel Curie point standards. (Courtesy of TA Instruments, New Castle, DE, www.tainst.com.)...

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