Derivation of the Critical Point Scaling Hypothesis Using Thermodynamics Only

Based on the foundations of thermodynamics and the equilibrium conditions for the coexistence of two phases in a magnetic Ising-like system, we show, first, that there is a critical point where the isothermal susceptibility diverges and the specific heat may remain finite, and second, that near the critical point the entropy of the system, and therefore all free energies, do obey scaling. Although we limit ourselves to such a system, we elaborate about the possibilities of finding universality, as well as the precise values of the critical exponents using thermodynamics only.

Point Defects Characterization in Quenched δ-Ni2Si as Deduced from Isothermal Magnetic Susceptibility Measurements

The behaviour of quenched defects in Ni2Si compound is studied by isothermal susceptibility magnetic measurements. In the range of temperature 553-593K, where an enhancement of susceptibility has been previously detected by isochronal measurements, an activation energy (EA=2.5 ± 0.2 eV) is determined. This value is in agreement with the break-up of 3D nickel vacancy clusters, formed at lower temperatures, and the subsequent formation of nickel rich defects via the released vacancies.

Calculation of the isothermal susceptibility by the Kubo formula

The relation between the zero frequency limit of the frequency-dependent susceptibility and the isothermal susceptibility is made clearer by expressing them in terms of the spectral density function. The general formulas are illustrated for the perpendicular susceptibilities of the Ising model.