  Using the experimental capability of the novel X-ray diffraction instrument
available at the 25 Tesla Florida Split Coil Magnet at the NHMFL, Tallahassee
we present an extensive investigation on the magnetostriction of
polycrystalline AlFe2B2. The magnetostriction was measured near the
ferromagnetic transition temperature (Curie temperature TC = 280 K, determined
via DC magnetization measurements), namely, at 250, 290, and 300 K. AlFe2B2
exhibits an anisotropic change in lattice parameters as a function of magnetic
field near the Curie temperature, and a monotonic variation as a function of
applied field has been observed, i.e., the c-axis increases significantly while
the a- and b-axes decrease with the increasing field in the vicinity of TC,
irrespective of the measurement temperature. The volume magnetostriction
decreases with decreasing temperature and changes its sign across TC. Density
functional theory calculations for the non-polarized and spin-polarized
(ferromagnetic) models confirm that the observed changes in lattice parameters
due to spin polarization are consistent with the experiment. The relationships
for magnetostriction are estimated based on a simplified Landau model that
agrees well with the experimental results.
