13 research outputs found
Strongly anisotropic magnetocaloric effect in a dipolar magnet LiGdF
We report the detailed study of the magnetocaloric effect (MCE) in a
dipolar-Heisenberg magnet LiGdF using magnetization measurements performed
on a single crystal sample. Entropy variation on isothermal demagnetization
from the magnetic field up to 3 T is determined in the temperature range 2-10 K
for two principal directions of the applied field (parallel and perpendicular
to the tetragonal -axis of the crystal). The MCE is found to be highly
anisotropic, with the cooling efficiency being up to twice higher at
. The results are nicely interpreted in the frame of a
conventional molecular field approach taking into account considerable
anisotropy of the paramagnetic Curie-Weiss temperature. These results are
compared to earlier studies of MCE in powder samples of LiGdF [T. Numazawa
et al., AIP Conf. Proc. 850, 1579 (2006)] as well as with analogous data for
other well known magnetocaloric materials. Our findings may open new
possibilities to enhance the efficiency of magnetic refrigeration in the liquid
helium-4 temperature range.Comment: 4 pages, 3 figure
Magnetic and spectral properties of multi-sublattice oxides SrY2O4:Er3+ and SrEr2O4
SrEr2O4 is a geometrically frustrated magnet which demonstrates rather
unusual properties at low temperatures including a coexistence of long- and
short-range magnetic order, characterized by two different propagation vectors.
In the present work, the effects of crystal fields (CF) in this compound
containing four magnetically inequivalent erbium sublattices are investigated
experimentally and theoretically. We combine the measurements of the CF levels
of the Er3+ ions made on a powder sample of SrEr2O4 using neutron spectroscopy
with site-selective optical and electron paramagnetic resonance measurements
performed on single crystal samples of the lightly Er-doped nonmagnetic
analogue, SrY2O4. Two sets of CF parameters corresponding to the Er3+ ions at
the crystallographically inequivalent lattice sites are derived which fit all
the available experimental data well, including the magnetization and dc
susceptibility data for both lightly doped and concentrated samples.Comment: 14 pages, 9 figure
Microscopic spin Hamiltonian for a dipolar-Heisenberg magnet LiGdF4 from EPR measurements
Low-temperature electron paramagnetic resonance measurements are performed on
single crystals of LiY_{1-x}Gd_xF_4 with weak x=0.005 and moderate x=0.05
concentration of Gd ions. Modeling of the experimental spectra allows us to
precisely determine microscopic parameters of the spin Hamiltonian of the
parent LiGdF4 material, including the nearest-neighbor exchange constant. The
obtained parameters are further tested by comparing a strongly anisotropic
Curie-Weiss temperature obtained for LiGdF4 in our static magnetization
measurements with theoretically computed values. We find a fine balance between
principal magnetic interactions in LiGdF4, which results in a hidden magnetic
frustration presumably leading to a delayed magnetic ordering and an enhanced
magnetocaloric effect at low temperatures.Comment: 6 pages, 6 figure