Magnetocaloric effect ofEr5Si4under hydrostatic pressure

Abstract

The magnetocaloric effect ͑MCE͒ of the compound Er 5 Si 4 has been investigated as a function of the applied magnetic field ͑up to 50 kOe͒ and the hydrostatic pressure ͑from ambient pressure up to 9 kbar͒. At constant magnetic field change, increasing the pressure up to 1.4 kbar induces a global rise of the magnetic entropy change, ͉⌬S mag ͉, with the peak at T C Х 30 K growing from 14.9 to 20.1 J / kg K. Between 1.4 and 9 kbar, the size and shape of the ͉⌬S mag ͉ vs T curve remain nearly constant but the peak moves to higher temperatures and stabilizes above 3.5 kbar at T ϳ 36 K. Contrary to many other R 5 ͑Si x Ge 1−x ͒ 4 compounds, the magnetocaloric effect in Er 5 Si 4 does not originate from the simultaneous field-induced magnetic and structural transformations since previous studies of the compound have demonstrated that moderate steady magnetic fields are not strong enough to induce the M → O͑I͒ transformation at the atmospheric pressure. However, the pressure dependence of the MCE is associated with pressure-induced M → O͑I͒ structural transformation that takes place in Er 5 Si 4 . The increase in the magnetic entropy change occurs because of a modification of the magnetic coupling derived from the differences in the interlayer bonding in the M and O͑I͒ states. This gives rise to an enhancement of the ferromagnetic interactions in the O͑I͒ phase with respect to the ambient pressure M state, resulting in a stronger saturation magnetization and a higher Curie temperature, i.e., T C M = 30 K and T C O͑I͒ =36 K.

Magnetism and magnetocaloric effect of single-crystal Er5Si4under pressure

“…These changes can be understood assuming a change from the M-FM state present at ambient pressure to the O(I)-FM state at high enough pressure. As was already discussed in the Introduction, magnetic, linear thermal expansion measurements and neutron diffraction experiments have shown that the hydrostatic pressures stabilizes the O(I)-FM phase in polycrystalline samples 15,16 . High applied field measurements 14 also evidences that the effect of the magnetic field at low temperatures is to produce a mixture of both phases M-FM and O(I)-FM , the volume of the O(I)-FM phase growing at the expense of the M-FM phase as the magnetic field increases.…”

“…On the other hand, hydrostatic pressure not only induces the O (I) phase at low temperature, but also shifts the high-temperature crystallographic change at a very high rate of dT t /dP ∼ -30 K/kbar 15 . This causes both transitions (the hightemperature crystallographic and the low-temperature magnetic ordering) to collapse at high pressures (above 6 kbar), which stabilizes the O (I)-Er 5 Si 4 over the whole temperature range maximizing the magnetocaloric effect at low temperature 16 . This low-temperature O (I) crystal structure has a Curie temperature T O(I) C = 35 K, higher than that of the monoclinic phase T M C = 30 K. The studies mentioned above have been performed on polycrystalline samples where some aspects of the physical behaviour may be masked or averaged out, mainly those associated with anisotropic properties.…”

“…The study of other compounds of the family with non-zero rare earth orbital momentum is necessary to understand the origin of magnetocrystalline anisotropy in these compounds and its relevance in the magnetocaloric properties. The use of hydrostatic pressure in these materials has demonstrated to be an interesting approach to analyse the coupling between the crystal structure and the magnetism 1,15,16,20,[24][25][26][27] . Thus, the aim of the present work is to investigate the magnetic properties of single crystalline Er 5 Si 4 under hydrostatic pressure.…”

Identifying the critical point of the weakly first-order itinerant magnet DyCo2with complementary magnetization and calorimetric measurements

“…9 The choice of R affects the lattice parameter, and as a result the bulk magnetic behavior via 4f-3d exchange. 10 Furthermore, the lattice parameter, a, can be tuned such that a small change in applied field, temperature, and/or pressure can induce magnetic order (7.05 Å < a < 7.22 Å), 6,11 and an associated volume change (or distortion) occurs to reduce the increase in energy due to overlap of 3d bands. If that volume change is sufficiently large, the phase transition will be first order 12 and itinerant electron metamagnetism occurs.…”

Magnetic and structural properties of single-crystalline Er5Si4

“…Recent experimental results obtained at various pressures, temperatures, and applied magnetic fields 18,19,[25][26][27][28][29][30] showed that in Er 5 Si 4 the orthorhombic (O-I) ↔ monoclinic (M) structural transition takes place at about T s = 200 K on cooling, and contrary to most of the R 5 T 4 systems, where structural and magnetic transitions are either concomitant or close to one another on the temperature scale, 6 the magnetic ordering transition occurs here at a much lower temperature (T order. = 30 K).…”