Magnetovolume and magnetocaloric effects in Er_{2}Fe_{17} (original) (raw)
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Magnetocaloric and magnetovolume effects in Er2Fe17
Physical Review B, 2012
Combining different experimental techniques, investigations in hexagonal P63/mmc Er2Fe17 show remarkable magnetovolume anomalies below the Curie temperature, TC. In particular, the spontaneous magnetostriction reaches 1.6×10−2 at 5 K and falls to zero well above TC, owing to short-range magnetic correlations. Moreover, Er2Fe17 exhibits direct and inverse mag-netocaloric effects (MCE) with moderate isothermal magnetic entropy ΔSM, and adiabatic tem-perature ΔTad changes [ΔSM∼ −4.7 J(kgK)−1 and ΔTad∼2.5 K near the TC, and ΔSM∼1.3 J(kgK)−1 and ΔTad ∼ −0.6 K at 40 K for ΔH= 80 kOe, respectively, determined from magnetization measurements]. The existence of an inverse MCE seems to be related to a crystalline electric field-level crossover in the Er-sublattice and the ferrimagnetic arrangement between the magnetic moments of the Er and Fe-sublattice. The main trends found experimentally for the temperature dependence of ΔSMand ΔTadas well as for the atomic magnetic moments are qualitatively well- described considering a mean-field Hamiltonian that incorporates both crystalline electric field and exchange interactions. ΔSM(T) and ΔTad(T) curves are essentially zero at∼150 K, the temperature where the transition from direct to inverse MCE occurs. A possible interplay between the MCE and the magnetovolume anomalies is also discussed.
Magnetic structure and magneto-volume anomalies in Er2Fe17 compound
Journal of Physics: …, 2011
Neutron powder diffraction shows that the intermetallic Er2Fe17 compound with hexagonal crystal structure has a ferrimagnetic ground state (TC = 303 K). At T = 5 K the magnetic moments of Fe sublattice (μ ~ 2 μB) are therefore antiparalell to those of the Er one (μ ~ 9 μB), all of them lying on the basal plane. This compound exhibits strong magneto-volume effects up to temperatures in the vicinity of TC. Neutron thermo-diffraction experiments also show an anomalous temperature dependence of the cell volume, including a negative thermal expansion coefficient below 300 K. In addition, a positive spontaneous volume magnetostriction is observed up to T ~ 400 K, with a maximum (ωS ~ 0.02) located at T = 5 K.
The magnetocaloric effect in Er2Fe17 near the magnetic phase transition
Journal of Physics: Condensed Matter
Recent investigations in R2Fe17 intermetallic compounds have evidenced that these materials present a moderate magnetocaloric effect (MCE) near room temperature. A series of accurate magnetization measurements was carried out to show that the value of the demagnetizing factor has a significant influence on the absolute MCE value of Er2Fe17. In addition, the critical exponents determined from heat capacity and magnetization measurements allow us to describe the field dependence of the observed MCE around the Curie temperature.
Intermetallics, 2011
We have synthesized three pseudo-binary (Ce,R)2Fe17 intermetallic alloys, where cerium has been partially substituted by R = Y, Pr and Dy, with the aim of tuning the Curie temperature (between 253 and 273 K) for obtaining the maximum magneto-caloric response of the alloys just below room temperature. The analysis of the x-ray powder diffraction patterns show that the three samples crystallize in the rhombohedral Th2Zn17-type crystal structure (space group View the MathML source). We report the temperature dependence of the isothermal magnetic entropy change, |ΔSM|(T), the magnetic field dependence of its maximum value, |ΔSMmax|(H), and the relative cooling power around the second-order magnetic transition for magnetic field changes μ0ΔHmax = 5 T. The collapse of the normalized ΔSM(θ)/ΔSMmax vs. temperature (where θ is a rescaled temperature) into a single master curve allows the extrapolation of |ΔSM|(T) curves for higher magnetic field changes, and/or the estimation of the temperature dependence of the magnetic entropy for other 2:17 pseudo-binary compounds. The lower values of |ΔSMmax| compared with those of the R2Fe17 compounds with R = Pr or Nd are explained in terms of the decrease of the saturation magnetization. The magnetic field dependence of the |ΔSMmax| indicates that only Pr1.5Ce0.5Fe17 alloy roughly follows a mean-field behaviour.