310 research outputs found
Magnetic properties of EuPtSi single crystals
Single crystals of EuPtSi, which crystallize in the BaNiSn-type
crystal structure, have been grown by high temperature solution growth method
using molten Sn as the solvent. EuPtSi which lacks the inversion symmetry
and has only one Eu site in the unit cell is found to be an antiferromagnet
with two successive magnetic transitions at = 17 K and = 16 K, as inferred from magnetic susceptibility, heat capacity and
Eu M\"ossbauer measurements. The isothermal magnetization data for [001] reveal a metamagnetic transition at a critical field = 1 T. The magnetization saturates to a moment value of 6.43 /Eu above 5.9 T (9.2 T) for [001] ([100]), indicating that
these fields are spin-flip fields for the divalent Eu moments along the two
axes. The origin of this anisotropic behaviour is discussed. A magnetic (H, T)
phase diagram has been constructed from the temperature dependence of
isothermal magnetization data. The reduced jump in the heat capacity at indicates a transition to an incommensurate, amplitude modulated
antiferromagnetic structure. The shape of the hyperfine field split M\"ossbauer
spectrum at provides additional support for the proposed nature of
this magnetic transition.Comment: 6 pages, 6 figures. Submitted to Phys. Rev.
Non-Langevin behaviour of the uncompensated magnetisation in nanoparticles of artificial ferritin
The magnetic behaviour of nanoparticles of antiferromagnetic ferritin has
been investigated by 57Fe Mossbauer absorption spectroscopy and magnetisation
measurements, in the temperature range 2.5K-250K and with magnetic fields up to
7T. Samples containing nanoparticles with an average number of Fe atoms ranging
from 400 to 2500 were studied. The value of the anisotropy energy per unit
volume was determined and found to be in the range 3-6 10**5 ergs/cm3, which is
a value typical for ferric oxides. By comparing the results of the two
experimental methods at large field, we show that, contratry to what is
currently assumed, the uncompensated magnetisation of the feritin cores in the
superparamagnetic regime does not follow a Langevin law. For magnetic fields
below the spin-flop field, we propose an approximate law for the field and
temperature variation of the uncompensated magnetisation which has so far never
been applied in antiferromagnetic systems. This approach should more generally
hold for randomly oriented antiferro- magnetic nanoparticles systems with weak
uncompensated moments.Comment: 11 pages, 11 figure
Enhanced conduction band density of states in intermetallic EuTSi (T=Rh, Ir)
We report on the physical properties of single crystalline EuRhSi and
polycrystalline EuIrSi, inferred from magnetisation, electrical transport,
heat capacity and Eu M\"ossbauer spectroscopy. These previously known
compounds crystallise in the tetragonal BaNiSn-type structure. The single
crystal magnetisation in EuRhSi has a strongly anisotropic behaviour at 2 K
with a spin-flop field of 13 T, and we present a model of these magnetic
properties which allows the exchange constants to be determined. In both
compounds, specific heat shows the presence of a cascade of two close
transitions near 50 K, and the Eu M\"ossbauer spectra demonstrate that
the intermediate phase has an incommensurate amplitude modulated structure. We
find anomalously large values, with respect to other members of the series, for
the RKKY N\'eel temperature, for the spin-flop field (13 T), for the spin-wave
gap ( 20-25 K) inferred from both resistivity and specific heat data,
for the spin-disorder resistivity in EuRhSi ( Ohm.cm) and
for the saturated hyperfine field (52 T). We show that all these quantities
depend on the electronic density of states at the Fermi level, implying that
the latter must be strongly enhanced in these two materials. EuIrSi
exhibits a giant magnetoresistance ratio, with values exceeding 600 % at 2 K in
a field of 14 T.Comment: 6 pages, 8 figure
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