ANOMALOUS THERMAL-EXPANSION IN YMN2, Y6MN23 AND YMN12

The thermal expansion coefficient alpha(T) of YMn2, Y6Mn23 and YMn12 i s presented in the temperature range 4.2-1000 K together with alpha(T) of YCo2 and YNi2. The strong variation of alpha(T) of the Y-Mn compou nds in their paramagnetic state is discussed under the assumption that there exist Mn atoms with different electronic configurations and the refore with different atomic volumes. Changes of the concentration of these different Mn atoms with temperature reveal this anomalous therma l expansion.