Journal of Alloys and Compounds 387 (2005) 6–8 The magnetic entropy changes in Gd 1-x C x alloys Dunhui Wang ∗ , Zhenghua Su, Songling Huang, Zhida Han, Wenqin Zou, Youwei Du National Laboratory of Solid State Microstructures and Jiangsu Provincial Laboratory for NanoTechnology, Nanjing University, Nanjing 210093, China Received 3 May 2004; received in revised form 1 June 2004; accepted 1 June 2004 Abstract A series of Gd 1-x C x (x = 0.025, 0.06, 0.09) alloys have been prepared by arc melting. The X-ray diffraction patterns indicate that about 2.5 at.% C is soluble in Gd metal. After introducing a small quantity of C into Gd, the Curie temperatures of these alloys increase. The refrigerant capacities of these alloys are larger than that of Gd. These results suggest that Gd 1-x C x alloys may be utilized as refrigerant in room temperature magnetic refrigeration. © 2004 Elsevier B.V. All rights reserved. PACS: 75.30Sg Keywords: Magnetic entropy; Gd 1-x C x alloys; Magnetic refrigeration 1. Introduction Magnetic refrigeration is based on the magnetocaloric effect (MCE), which describes the adiabatic temperature change of materials produced by the magnetic entropy change (|S M |) upon the application and removal of a magnetic field. It is becoming a promising technology, replacing the conven- tional gas compression–expansion technology, owing to its potential impact on energy savings and environmental con- cerns. Until now, the MCE have been extensively studied in two kinds of working substance for magnetic refrigeration: paramagnetic salts and ferromagnetic compounds. The for- mer have been conveniently used to obtain low temperatures, T < 20 K, while the latter are useful for magnetic refrigera- tion at high temperature, T > 20 K. For obvious reason, the magnetic materials that show a large MCE around room tem- perature and in low magnetic fields are especially desirable. Large MCEs have been found in many magnetic materials, which have a first-order transition [1–4]. The most important ∗ Corresponding author. Tel.: +86 25 83594588; fax: +86 25 83595535. E-mail address: wangdh@nju.edu.cn (D. Wang). feature of these materials is that they undergo a simultane- ous structural and magnetic phase transition, which leads to a giant magnetic-entropy change across its ordering temper- ature [5]. Unfortunately, a first-order transition is always as- sociated with thermal or field hysteresis. This hysteresis will result in a reduced efficiency of the refrigeration cycle as it may be considered as a dead loop. This will be especially of importance if one wants to work in a low magnetic field [5]. Up to date, the most useful room temperature magnetic working substance is gadolinium metal, a rare earth element that undergoes a second-order transition at the Curie tem- perature (T C ). It is proved to be superior to many materials which have a first-order transition in practical application [6]. Recently, American scientists demonstrated the world’s first room-temperature, permanent magnet, magnetic refrigerator, which just utilized Gd as its working substance [7]. In order to search for other good candidates for room temperature re- frigeration, many binary Gd–R (R = other rare earth, such as Tb, Ho, Dy and Y) alloys have been studied [8]. According to the experimental results, their T C and |S M | are all lower than that of Gd. In this paper, we introduce small quantities of C atom into Gd and for obtaining Gd 1-x C x alloys, and 0925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2004.06.031