The magneto-caloric effect (MCE) of arc-melted bulk and 10 h ball-milled nanostructured Pr2Fe17 powders has been investigated. The maximum value for the magnetic entropy change, |ΔSM|, in the milled alloy is 4.5 J kg−1 K−1 for μ0H = 5 T, at around room temperature. The full width at half maximum, δTFWHM, of |ΔSM|(T) for the nanostructured powders is about 60% greater than that of the starting bulk alloy, thus giving rise to large relative cooling power values of 573 J kg−1 (4.5 J cm−3) for μ0H = 5 T estimated from the product of |ΔSM|max × δTFWHM. These results have been compared with those of well-known magnetic materials that exhibit a large or giant MCE effect. The potential for using these low-cost iron based nanostructured Pr2Fe17 powders in magnetic refrigeration at room temperature is also discussed.
The Heusler alloy Ni 50 Mn 37 Sn 13 was successfully produced as ribbon flakes of thickness around 7-10 m melt spinning. Fracture cross section micrographs in the ribbon show the formation of a microcrystalline columnarlike microstructure, with their longer axes perpendicular to the ribbon plane. Phase transition temperatures of the martensite-austenite transformation were found to be M S = 218 K, M f = 207 K, A S = 224 K, and A f = 232 K; the thermal hysteresis of the transformation is 15 K. Ferromagnetic L2 1 bcc austenite phase shows a Curie point of 313 K, with cell parameter a = 0.5971͑5͒ nm at 298 K, transforming into a modulated 7M orthorhombic martensite with a = 0.6121͑7͒ nm, b = 0.6058͑8͒ nm, and c = 0.5660͑2͒ nm, at 150 K. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2832330͔Ferromagnetic shape memory alloys ͑FSMA͒ are of considerable interest because of their exceptional magnetoelastic properties.1-3 The shape memory effect can not only be controlled by changing the temperature, as it occurs in traditional shape memory alloys, but also by varying the magnetic field up to moderate field values. The latter makes them of noteworthy interest for developing new thermal or magnetically driven actuators. 4Among the Heusler alloys that exhibit magnetic shape memory effect, the most extensively studied are those of the Ni-Mn-Ga system. However, to overcome some of the problems related to practical application, such as the high cost of gallium and the low martensitic transformation temperature that they usually present, the search for Ga-free alloys has been recently attempted. Martensitic transformation in ferromagnetic Heusler Ni 50 Mn 50−x Sn x alloys with 10ഛ x ഛ 16.5 was first reported by Sutou et al. 5 Later, Krenke et al. studied phase transformations and magnetic and magnetocaloric properties of the Ni 50 Mn 50−x Sn x alloy series with 5 ഛ x ഛ 25. 6,7 Samples with x = 0.13 and 0.15 are ferromagnetic in the martensitic state undergoing a first order martensitic-austenitic structural transition at a temperature below the respective Curie points of both phases. At room temperature, the alloy with x = 0.13 is martensitic, and the martensite-austenite transformation occurs around room temperature. Brown et al. 8 12 They report magnetic entropy changes up to 10.4 J / kg K at 10 kOe for x = 7. Ni-Mn-Sn system is, therefore, of prospective importance as FSMA and as promising magnetic refrigerant alloy. In all these cases, alloys were produced as bulk polycrystalline samples.In this work we produced, as far as we know for the first time, Ni-Mn-Sn alloys by rapid solidification. This procedure offers several potential advantages for the fabrication of the shape memory materials such as avoiding the homogenization annealing step to reach a single phase alloy and the synthesis of highly textured polycrystalline samples. Moreover, ribbon shape is appropriate for direct use in practical devices. In view of its interesting properties, 6,7 we have selected the alloy Ni 50 Mn 37 Sn 13 and studied its microstr...
The temperature dependence of the isothermal magnetic entropy change, ΔS M , and the The ideal Ericsson cycle (two isothermal and two isomagnetic field processes) is optimal for RT applications [2]. Its maximum efficiency is reached when the MCE exhibits a constant temperature dependence of the isothermal magnetic entropy change, ΔS M (T), within the operating temperature range [3]. This condition is difficult to be accomplished by a single material, but a composite made of two ferromagnetic materials may fulfill it provided that the difference between their Curie points, T C , is customized [4]. However, sintered mixtures of compounds are not well suited because they behave as a material with a single T C [5]. Instead of that, the design of specific composites [6][7][8] can lead to an enlargement of the MCE temperature span and an almost constant ΔS M (T) curve. The efficiency of the magnetic material in terms of the energy transfer between the cold (T cold ) and hot (T hot ) reservoirs, is quantified by its refrigerant capacity, RC, an important figure of merit that characterizes the magnetocaloric material [9,10]:where T cold and T hot are commonly selected as the temperatures corresponding to the full width at half maximum of ΔS M (T). In order to attain large RC values, a large magnetic entropy change over a wide temperature range is desirable. However, it has been shown that although the maximum value of ΔS M decreases, a large broadening of the ΔS M (T)curves can overcompensate such decrease, giving rise to a significant RC enhancement [7,10]. In turn, numerical calculations and their proof-of-principle in practical systemsshow that the design and practical realization of multiphase or composite magneto-3 caloric materials with optimized RC and ΔS M (T) curves is not a simple task [4][5][6]. For a two-phase composite the magnetic field variation of the RC is complex, and depends on several factors such as ΔT C and the shape, width and peak value of ΔS M (T) curve of the two constituents [6].In this letter we report on the MCE in a two-ribbon composite showing a larger RC with respect to that of each individual ribbon and a flattened ΔS M (T) curve. The composite is formed by two Fe-rich FeZrB(Cu) amorphous ribbons. These alloys, which were extensively studied due to their re-entrant spin-glass fig. 3). This RC enhancement is a consequence of the increase in δT FWHM . Nevertheless, a compromise between the value of the δT FWHM and the potential lost of efficiency of the machine (due to an increase of cycles in the heat exchange medium) is needed. In turns, the ΔS comp (T) curves under low magnetic field changes (μ o ∆H < 0.4 T) exhibit a double-peak profile [see inset of Fig. 2(a)], and the δT FWHM cannot be properly defined. 5Both, the enhancement of RC comp and the flattening observed in the ΔS comp curve stimulated us to measure the M(H) curves for the two-ribbon composite. This is important in order to assess whether the shape of M(H) curves is in some extend affected by dipolar interactions between ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.