Abstract
R. S. Manna, P. Das, M. de Souza, F. Schnelle, M. Lang, J. Müller, S. von Molnár, Z. Fisk
The coupling of magnetic and electronic degrees of freedom to the crystal lattice in the ferromagnetic
semimetal EuB6, which exhibits a complex ferromagnetic order and a colossal magnetoresistance effect, is
studied by high-resolution thermal expansion and magnetostriction experiments. EuB6 may be viewed as a
model system, where pure magnetism-tuned transport and the response of the crystal lattice can be studied
in a comparatively simple environment, i.e., not influenced by strong crystal-electric field effects and Jahn-
Teller distortions.We find a very large lattice response, quantified by (i) the magnetic Grüneisen parameter,
(ii) the spontaneous strain when entering the ferromagnetic region, and (iii) the magnetostriction in the
paramagnetic temperature regime. Our analysis reveals that a significant part of the lattice effects originates
in the magnetically driven delocalization of charge carriers, consistent with the scenario of percolating
magnetic polarons. A strong effect of the formation and dynamics of local magnetic clusters on the lattice
parameters is suggested to be a general feature of colossal magnetoresistance materials.