Temperature ordering

AHoy Crystal stmcture Critical ordering temperature, T °C °F Mp, °C Material density, g/em Young s modulus, GPa... 

Response of a Second-Order Temperature Measuring Element... 

It is known that below the ordering temperature, the — ASM of a paramagnet will quickly reduce to zero, thus defining the temperature range in which the material can be usefully employed. Note that gadolinium metal works best at room temperature, which constitutes a separate and productive area of research with... 

The low-temperature limit of magnetic thermometry with paramagnetic salts (see Section 9.9) is given by the ordering temperature of the electronic magnetic moments. Such ordering temperature is around 1 mK (example the CMN thermometer). 

The complexity of the crystal structure of the [M(Cp )2][M (bdt)2] salts and the large number of intermolecular contacts in this series of complexes prevents a clear interpretation of the magnetic behavior and a correlation between the crystal structures and the magnetic properties. However, the saturation magnetization value in the case of the compounds [Mn(Cp )2][M (bdt)2] (M = Ni and Pt) is consistent with a D+A- AF coupling. A similar coupling is expected to occur in [Fe(Cp )2][M (bdt)2] (M = Ni and Pt), where %T shows a similar behavior, typical of a FIM above the ordering temperature. 

As far as the size of the exchange integral J between the two open-shell centres is concerned, it can become as high as a few tenths of an eV in diradicals (see Section 3). The /-values between radicals are usually smaller than 0.01 eV. Therefore, we cannot readily expect spin-ordering temperatures higher than a few to 20 K for intermolecular spin alignment. 

By contrast, if the two sub-lattices are totally occupied by different species the structure exhibits full long-range order, (Iro). In the binary case, and for the equiatomic composition, this is then represented by a separate symbol, B2 (Fig. 7.1). Between 0 K and the ordering temperature there is a finite degree of order expressed in terms of the occupation probabilities (tj) of the two sub-lattices a and /3... 

Approximate derivation o Tobwg)- Given values of and the basic BWG treatment also leads to explicit equations for the ordering temperature, T ", but the omission of sro inevitably leads to calculated values that are appreciably higher than shown by experiment. If the simplicity of the BWG method is to be retained, an empirical correction factor (x) has to be included, where X = Typical equations for various structural transitions are given... 

Integration of experimental Cp data with temperature can be used to bypass the plethora of models described in the previous sections, as it provides both the critical ordering temperature and the ratio of sro to Iro. This route has been extensively used to describe magnetic transformations (Inden 1977a, Hillert and Jarl 1978, Nishizawa et al. 1979) and generalised through the develq)ment of a series of approximate... 

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