Large Isothermal Entropy Change Research Articles

Effect of Ni substitution on the magnetic and magnetocaloric properties of the Dy(Co1−xNix)2 Laves phase

Structural, magnetic and magnetocaloric properties of Dy(Co1−xNix)2 (x = 0, 0.02, 0.04, 0.06 and 0.1) alloys were studied by x-ray diffraction (XRD) and magnetic measurements. The XRD analysis shows that all samples crystallize in the cubic MgCu2-type structure. The ordering temperature TC decreases from 143 to 92 K with increasing Ni content up to 0.1, which is attributed to the decrease in the exchange interactions. The isothermal entropy changes ΔS as a function of temperature in different magnetic fields were determined. All samples show a large isothermal entropy change and ΔSmax remains approximately constant over the temperature range limited by the Curie temperatures of the Dy(Co1−xNix)2 series (92–143 K). The relative cooling power increases with the Ni content; it passes from 287 to 344 J kg−1 for x varying from 0 to 0.1 under 5 T. The origin of the magnetocaloric effect in Dy(Co1−xNix)2 alloys is discussed.

Application of Large Magnetocaloric Effects in Itinerant-Electron Metamagnets to Cooling Systems

The La(FexSi1-x)13 compounds exhibit large magnetocaloric effects (MCEs) due to the itinerant-electron metamagnetic (IEM) transition. By hydrogen absorption, the Curie temperature TC increases up to room temperature with retaining the IEM transition. The La(Fe0.90Si0.10)13H1.1 compound indicates a large isothermal magnetic entropy change of ∆Sm = - 28 J/kg K at 287 K in the magnetic field change from 0 to 2 T (∆B = 2 T). In addition, the MCEs are enhanced by partial substitution of Ce for La. The value of TC for La(FexSi1-x)13 is decreased by partial substitution of Mn for Fe, keeping excellent MCEs. Consequently, the La(FexSi1-x)13 and their modified compounds are promising as magnetic refrigerants working at a wide range of temperature covering room temperature.

Enhancement of isothermal entropy change due to spin fluctuations in itinerant-electron metamagnetic La(Fe 0.88Si 0.12) 13 compound

A large isothermal entropy change in La(Fe 0.88Si 0.12) 13 itinerant-electron metamagnetic (IEM) compound has been investigated by using the Maxwell and Clausius–Clapeyron relations. The entropy change obtained from the Clausius–Clapeyron relation Δ S m CC gradually decreases with increasing temperature, while that from the Maxwell relation Δ S m Mx in the magnetic field of 2 T shows a plateau-like behavior in 195–203 K. The difference between Δ S m Mx and Δ S m CC is mainly explained by the entropy change in the paramagnetic (P) state below the critical magnetic field of the IEM transition B C. In the P state, the temperature dependence of susceptibility χ p is enhanced by spin fluctuations. The thermal variation of Δ S m Mx − Δ S m CC is well represented by taking that of χ p as well as B C into account. Therefore, the plateau-like behavior of Δ S m Mx comes from the enhancement of the entropy change in the P state, which cancels the decrease of Δ S m CC due to the decrease of latent heat of the IEM transition with increasing temperature.