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Table-like magnetocaloric effect is an important requirement for obtaining high efficiency performance in magnetic refrigeration that uses Ericsson cycle. Magnetic and magnetocaloric properties of Ho 36 Co 48 Al 16 alloy, carefully selected from multiphase region of the ternary Ho-Co-Al system, have been studied. The multiphasic alloy exhibits three magnetic phase transitions spread over a wide temperature range. Suitable distribution of phase proportions and respective magnetic entropy changes result in the broadening of the overall peak magnetic entropy change of the alloy. Table-like magnetocaloric effect is obtained with magnetic entropy change of 8.5 J/kg K and large refrigerant capacity of 525 J/kg under applied magnetic field change of 0–5 T. At field change of 0–2 T, the magnitude of the magnetic entropy change plateau is 2.9 J/kg K with refrigerant capacity of 180 J/kg. The table-like feature and the competitive refrigerant capacity and applied magnetic field change values make the multiphase alloy a practical magnetic refrigerant for efficient low temperature cooling applications that employ the Ericsson cycle, even under permanent magnets. [ABSTRACT FROM AUTHOR]

The effects of Co substitution on the structure, magnetic properties, and magnetocaloric effect of Gd 3 Ru 1− x Co x (0.05 ≤  x  ≤ 0.20) alloys have been investigated by X-ray diffraction and magnetization measurements. The Curie temperatures varied between 60 K and 92 K with Co substitution for Ru. With an applied magnetic field change ( ΔH ) of 50 kOe, the maximum values of magnetic entropy change (−Δ S M ) were determined to be 25.8, 23.1, 19.4, and 10.8 J/kg K for compositions with x  = 0.05, 0.10, 0.15, and 0.20, respectively. The corresponding refrigeration capacities ( RCs ) for the alloys were reasonably large and calculated to be 495, 475, 467, and 517 J/kg. The magnetic phase transitions in the Gd 3 Ru 1− x Co x (0.05 ≤  x  ≤ 0.15) alloys are of first-order. In the Gd 3 Ru 0.80 Co 0.20 , the first-order magnetic phase transition disappears and the transition is broadened hence it increases in RC . The high −Δ S M values and accompanying large RC s for the Gd 3 Ru 1− x Co x (0.05 ≤  x  ≤ 0.20) alloys qualify them as potential candidates for magnetic refrigeration applications near liquid nitrogen temperature. [ABSTRACT FROM AUTHOR]

The R 2 Co 2 Al compounds (R = Tb, Dy, Ho, Er, Tm) are known to contain RCoAl-type impurity. In order to suppress the impurity phase in Ho 2 Co 2 Al intermetallic compound, nonstoichiometric samples with excess rare-earth Ho were prepared and annealed. Structural analysis indicates that annealed nonstoichiometric Ho 42 Co 40 Al 20 sample, with 2 at% excess Ho, comprises the Ho 2 Co 2 Al phase and minor traces of Ho 2 O 3 oxide. Magnetic and magnetocaloric properties of the sample have been studied in detail. The alloy undergoes three phase transitions at 9 K, 21 K and 30 K. The multiple transitions and broadening effect of second-order phase transitions (SOT) on peak magnetic entropy change (−Δ S M ), result in good refrigerant capacities ( RC area s) of 136.9 and 437 J/kg under field changes (Δ H ) of 2 and 5 T, respectively. These values of RC area and their corresponding large −Δ S M peak magnitudes of 9.1 and 18.4 J/kg K under Δ H = 2 and 5 T, respectively, make Ho 2 Co 2 Al a promising and competitively good candidate magnetic refrigerant for low temperature cooling applications such as liquefaction of hydrogen gas. [ABSTRACT FROM AUTHOR]

This paper presents the structure, magnetic properties, and magnetocaloric effect of the polycrystalline compound GdNiAl 2 . Powder X-ray diffraction (XRD) measurement and Rietveld refinement revealed that GdNiAl 2 alloy is CuMgAl 2 -type phase structure with about 1 wt% GdNi 2 Al 3 secondary phase. Magnetic measurements suggest that the compound is ferromagnetic and undergoes a second-order phase transition near 28 K. The maximum value of magnetic entropy change reaches 16.0 J/kg K for an applied magnetic field change of 0–50 kOe and the relative cooling power was 6.4×10 2 J/kg. It is a promising candidate as a magnetocaloric material working near liquid hydrogen temperature (~20 K) exhibiting large relative cooling power. [ABSTRACT FROM AUTHOR]