Lattice dynamics and phase transitions

Anomalies in thermal expansion of rare-earth diborides in the temperature range of magnetic phase transformations

V. V. Novikov^a, T. A. Chukina^a, A. A. Verevkin<sup>b

a</sup> I. G. Petrovsky Bryansk State University
^b Electrical Engineering Department, University at Buffalo, SUNY, Amherst, N.Y., USA

Abstract: The variations with temperature of the lattice parameters $a(T)$ and $c(T)$ and the thermal expansion coefficients of rare-earth diborides RB$_2$ (R = Tb, Dy, Ho, Er, Tm, Lu) have been investigated in the temperature range 4.2–300 K. It has been revealed that the dependences $a(T)$ and $c(T)$ exhibit an anomalous behavior in the vicinity of the ferromagnetic transformation temperatures $T_c$ which correlates with the temperature dependences of the heat capacity. It has been established that the magnetic contributions to the thermal expansion of the diborides $\Delta a_m(T)$ increase with increasing temperature and tend to constant values at $T\gg T_c$ and that the magnetic components $\Delta c_m(T)$ decrease for all the diborides studied, also tending to constant values at elevated temperatures. The exchange integrals $Y_a$ and $Y_c$ for the paramagnetic metal ions in the rare-earth diborides are determined from the dependences $\Delta a_m(T)$ and $\Delta c_m(T)$.

Received: 15.01.2009
Accepted: 23.04.2009

 English version: Physics of the Solid State, 2010, 52:2, 364–369

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