Abstract
The magnetic ordering structure of GdPO4 is determined at T = 60 mK by diffraction of hot
neutrons with wavelength λ = 0.4696 ˚A. It corresponds to a non-collinear antiferromagnetic arrangement
of the Gd moments with propagation vector k = (1/2, 0, 1/2). This arrangement is
found to minimize the dipole-dipole interaction and the crystal field anisotropy energy, the magnetic
superexchange being much smaller. The intensity of the magnetic reflections decreases with
increasing temperature and vanishes at T 0.8 K, in agreement with the magnetic ordering temperature
TN = 0.77 K, as reported in previous works based on heat capacity and magnetic susceptibility
measurements. The magnetocaloric parameters have been determined from heat capacity data at
constant applied fields up to 7 T, as well as from isothermal magnetization data. The magnetocaloric
effect reaches ΔST = 375.8 mJ cm3 K
1 at T = 2.1 K, largely exceeding the maximum values
reported to date for Gd-based magnetic refrigerants.