This book contains the unfinished manuscript and working notes of the book Merleau-Ponty was writing when he died.

The use of electric arc furnace and DyGa1.8Cu0.2 prepared DyGa2 alloy samples. By X-ray powder diffraction and magnetic measurements of the two alloys studied crystal structure and magnetic properties. The results show that: DyGa2 and DyGa1.8Cu0.2 The crystal structure P6/mmm hexagonal structure, with a small amount of Cu Ga can substitute smaller cell volume. DyGa2 and DyGa1.8Cu0.2 Nair temperature alloys, respectively 16K and 113K, occur at temperatures below the temperature Nair paramagnetic - antiferromagnetic phase transition, and phase transitions of type (...) two phase transition. DyGa2 in the 8K near metamagnetic transition temperature for a phase transition. DyGa2 maximum magnetic entropy change is 7.3J /, with a strong magnetic refrigeration capacity of about 131J/kg, in the 5K near-14.9J / of the abnormal negative magnetic entropy change so DyGa2 with self-regulating function of temperature. A small amount of Cu-doped alloy magnetic refrigeration temperature will increase to near 100K, magnetic refrigeration has a good potential for application development. The crystal structures and magnetocaloric effect of DyGa2 and DyGa1.8Cu0.2 compounds were studied by X-ray powder diffraction and magnetic measurements. The main results show that the crystal structures of compounds are hexangular structure with space group of P6/mmm, and the cell volume decreases when Ga atoms are substituted by Cu atoms. The Neel temperatures of DyGa2 and DyGa1.8Cu0.2 are 16 and 113 K, respectively. They are anti-ferromagnetic below Neel temperature, which become paramagnetic near Neel temperature. The kind of this phase transiton is second order phase transition. The M vs. H curves for T ≤ 8 K exhibit features that resemble those of a metamagnetic transformation which is first order phase transition. For a magnetic field change of 50 kOe, the maximum values ​​of - ΔS for DyGa2 is 7.3 J • kg ^ • K ^, and cooling power is 131 J • kg ^. The values ​​of-ΔS for DyGa2 is unconventionally negative • K ^ ) at about 5 K. The phenomenon can be used in temperature control. A small amount of Cu doping makes the magnetic refrigeration temperatures to about 100 K. They are potential candidates for the practical magnetic refrigeration. (shrink)