Magnetic Cooling Page

Systematic study of the microstructure, entropy change and adiabatic temperature change in optimized LaFeSi alloys

A systematic study of microstructure and magnetocaloric effect in LaFe_11.8Si_1.2 and LaFe_11.6Si_1.4 alloys over a large range of annealing temperatures and times has been carried out. With the aim to obtain the pure 1:13 phase and maximum magnetic entropy change, the annealing temperature is optimized to 1373 K for LaFe_11.8Si_1.2 and 1323 K for LaFe_11.6Si_1.4. We found a unique morphology of eutectoid-type lamellae, which is suggested to be an intermediate phase upon formation of the 1:13 phase. Adiabatic temperature change ∆T_ad measurements were employed to assess directly the magnetocaloric effect. By application of a magnetic field of 1.9 T, large ∆T_ad values of 7.3 K and 7.0 K in the vicinity of the transition temperatures were found for LaFe_11.8Si_1.2 and LaFe_11.6Si_1.4, respectively, after optimized annealing. By considering the partial irreversibility of magnetostructural transition, the influence of thermal and magnetic hysteresis on magnetic entropy change and ∆Tad is also discussed.

J. Liu, M. Krautz, K. Skokov, T.G. Woodcock, O. Gutfleisch, Acta Mater. 59 (2011) 3602-3611, pdf

Peculiarities of the magnetocaloric properties in Ni-Mn-Sn ferromagnetic shape memory alloys

Magnetocaloric properties of a Ni₅₀Mn₃₆Co₁Sn₁₃ ferromagnetic shape memory alloy have been studied experimentally in the vicinity of a first-order magnetostructural phase-transition low-temperature paramagnetic martensite ↔ high-temperature ferromagnetic austenite. The magnetic entropy change ΔSm calculated from the magnetization M(T) data measured upon cooling is higher than that estimated from M(T) measured upon heating. Contrary to ΔSm, the adiabatic temperature change ΔTad measured upon cooling is significantly smaller than that measured upon heating.

V. V. Khovaylo et al., Phys. Rev. B 81 (2010) 214406, pdf

Contributions to the entropy change in melt-spun LaFe_11.6Si_1.4

Here we study the calorimetric and magnetic behaviour of melt-spun LaFe_11.6Si_1.4, a potential magnetic refrigerant material system that exhibits the rare combination of a large entropy change and low thermal and magnetic field hysteresis. We are able to separate the calorimetric contribution from latent heat and changes in equilibrium heat capacity explicitly by using two separate calorimetric probes. The heat capacity of this sample exhibits significant changes of the order of 500–1000 J K^–1 kg^–1 in response to magnetic field that results in large changes in entropy.

K. Morrison et al., J. Phys. D: Appl. Phys. 43 (2010) 132001, pdf

Magnetic and magnetocaloric effect in melt spun La_1−xR_xFe_13−yAl_yC_z (R = Pr and Nd) compounds

In this paper, we report the structural, magnetic and magnetocaloric effect (MCE) of La_1−xR_xFe_13−yAl_yC_z (R = Pr and Nd, x = 0.1 and 0.2, y = 1.5 and 1.6 and z = 0.02 and 0.04) compounds. Temperature dependence of magnetization data shows second order and ferromagnetic transition for all compounds. MCE has been calculated in terms of isothermal (ΔSM) using the magnetization isotherms obtained at transition temperature close to transition temperature. The maximum values of ΔSM vary between ~3 to ~5 and ~5.2 to ~8.3 J kg⁻¹K⁻¹ for a field change of 20 kOe and 50 kOe, respectively, whereas relative cooling power is ~140 to ~230 and ~396 to ~556 J kg⁻¹ for the same field change.

P. Kumar et al ., J. Phys. D: Appl. Phys. 42 (2009) 205003, pdf

La(Fe,Si)₁₃-based magnetic refrigerants obtained by novel processing routes

The structure and magnetic properties of LaFe_13−xSi_x and Co-substituted LaFe_11.8−xCo_xSi_1.2 alloys prepared by melt spinning, as well as of LaFe_11.57Si_1.43H_x hydrides prepared by reactive milling are investigated. The hysteresis in the temperature- and field-induced phase transitions is significantly reduced as compared with conventional bulk alloys, which makes these materials very attractive for magnetic refrigerant applications. The unusual combination of features characteristic of first- and second-order phase transitions in the La(Fe,Si)₁₃-based compounds is discussed on the basis of density-functional electronic structure calculations.

J. Lyubina et al., J. Magn. Magn. Mater. 320 (2008) 2252-2258, pdf

Effect of pressure on the magnetocaloric properties of nickel-rich Ni–Mn–Ga Heusler alloys

Nickel-rich Ni–Mn–Ga Heusler alloys were prepared by arc melting and subsequent homogenization by annealing. A large magnetic entropy change was observed around 291 K in the alloy where martensite-austenite structural and ferro-para magnetic transitions almost coincide with each other. The effect of hydrostatic pressure of up to 8 kbar on magneto-structural transitions, magnetocaloric effect, and magnetic hysteresis was studied.

K. Mandal et al., J. Appl. Phys. 105 (2009) 073509-073509-6, pdf

Magnetocaloric Effect in Ni–Mn–Ga Alloys

Heusler alloys with nickel rich nominal composition Ni_2+xMn_1-xGa (x = 0.16 - 0.26) were prepared by arc-melting and subsequent homogenization by annealing. A large magnetic entropy change around room temperature was observed in the alloy where martensite-austenite structural and ferro-para magnetic transition temperatures almost coincide with each other. It also shows large hysteresis in the magnetization isothermals. A sharp peak in the specific heat versus temperature curve indicates a first-order transition at the temperature of large entropy change.

K. Mandal et al., IEEE Trans. on Magnetics 44 (2008) 2993-2996, pdf

Multiple Metamagnetic Transitions in the Magnetic Refrigerant La(Fe,Si)₁₃H_x

The effect of hydrostatic pressure on thermally and field-induced first-order magnetic phase transitions is studied in the La(Fe,Si)₁₃-type compounds. A peculiar series of consecutive field-induced transitions is realized using a distinct combination of hydrostatic pressure and negative pressure created by the interstitial insertion of hydrogen. The pressure-induced discontinuous magnetization jumps result in an enhanced cooling power, thus opening up the possibility to exploit in full the magnetocaloric potential of this compound class.

J. Lyubina et al., Phys. Rev. Lett. 101 (2008) 177203, pdf

Reversibility of magnetostructural transition and associated magnetocaloric effect in Ni–Mn–In–Co

By analyzing isothermal magnetization curves under magnetic field cycling, the reversibility of the magnetostructural transition was investigated in Ni–Mn–In–Co in form of bulk sample and melt-spun ribbons. The hysteresis of thermally/magnetically induced martensitic transformation plays an important role in the reversibility of the magnetostructural transition. In ribbons with a large hysteresis of 18 K, residual field-induced austenite is present after removing the magnetic field, while, in the bulk sample, the magnetostructural transition is reversible at moderate temperatures due to a relatively smaller hysteresis of 8 K.

J. Liu et al., Appl. Phys. Lett. 93 (2008) 102512, pdf

Magnetocaloric effect in LaFe_11.8-xCo_xSi_1.2 melt-spun ribbons

The structure and magnetic entropy changes in melt-spun and annealed LaFe_11.8−xCo_xSi_1.2 (x = 0, 0.4 and 0.8) ribbons have been investigated. The magnetic entropy change in the LaFe₁₁Co_0.8Si_1.2 ribbons is higher than that reported in the bulk counterpart and that of conventional MCE materials, such as pure Gd.

A. Yan et al., J. Alloy. Comp. 450 (2008) 18, pdf

Magnetocaloric effect in reactively-milled LaFe_11.57Si_1.43H_y intermetallic compounds

Hydrides of LaFe_11.57Si_1.43 intermetallic compound have been prepared by high-energy ball milling in the presence of hydrogen gas, a process known as reactive milling. The present study indicates that reactive milling can be an effective method for incorporating interstitial hydrogen within these compounds in order to raise their TC to room temperature.

K. Mandel et al., J. App. Phys. 102 (2007) 053906, pdf