Anomalous Thermal Expansion and Spontaneous Magnetostriction of Gd2Fe16.5Cr0.5 Compound

The thermal expansion and magnetic properties of Gd2Fe16.5Cr0.5compound have been investigated by means of X-ray diffraction and magnetization measurements. The Gd2Fe16.5Cr0.5compound has a rhombohedral Th2Zn17-type structure. The Curie temperature of Gd2Fe16.5Cr0.5compound is about 560K. This value is about 50K higher than that value of the mother compound Gd2Fe17. A small average thermal expansion coefficient, = 1.65×10-6/K, and a negative average thermal expansion coefficient, = -1.46×10-5/K, were found in Gd2Fe16.5Cr0.5compound by X-ray diffraction in the temperature range 294 - 514K, and 514-613K, respectively. There exists anisotropic strong spontaneous magnetostriction in the magnetic state of Gd2Fe16.5Cr0.5compound.

Relationship between the Spontaneous Magnetization, Spontaneous Magnetostriction and Heat Capacity in the Compound Mn5Ge3

Spontaneous magnetization Ms of the ferromagnetic compound Mn5Ge3 with the Curie temperature TC=305 K has been studied in the temperature range from 2 to 400 K. The relationships between the magnetic part of the heat capacity (CMAG), the magnetic part of the volume thermal expansion coefficient (TEC) MAG, and the Ms for the compound Mn5Ge3 have been considered. It has been found that the magnetic part of the heat capacity can be well approximated by the dependence CMAG(T)=a×|dMs2/dT|–b×|dMs4/dT| with a>0 and b>0, and the magnetic part of the TEC, by the dependence  MAG=C1×dMs2/dT+C2×dMs4/dT with C1<0 and C2>0 in the whole temperature. It is assumed that the main sources in the formation of the observed CMAG(T) and MAG(T) dependences are the changes in the elastic, magnetoelastic, magnetovolume, and magnetostatic energies of the sample that appear as a result of the spontaneous magnetostrictive deformation with temperature changing.