High Temperature Thermal Expansion of RMn2 Intermetallic Compounds with Heavy Rare Earth Elements

The temperature variation of the thermal expansion coefficient, α, of cubic and hexagonal Laves phase compounds RMn2(R=Gd ÷ Lu and Y) was measured in a wide temperature range 5-900 K by the X-ray diffraction and dilatometric methods. The value of α is substantially enhanced, up to 55x10-6 K-1, in the paramagnetic region. At high temperatures, 600–800 K, α passes over a maximum and decreases with a further increase of temperature. Some change in α(T) depending on the type of the rare earth ion was discovered suggesting the instability of the Mn electronic structure related to the strong temperature dependence of the mean squared amplitude of spin fluctuations.