JOURNAL OF RARE EARTHS, Vol. 29, No. 5, May 2011, P. 474 Foundation item: Project supported by the National Basic Research Program of China (2006CB601101), the National High Technology Research and Development Program of China (2007AA03Z440), and the National Natural Science Foundation of China (50731007) Corresponding author: LONG Yi (E-mail: longy@mater.ustb.edu.cn; Tel.: +86-10-62334807) DOI: 10.1016/S1002-0721(10)60482-6 Magnetocaloric effect and magnetic properties of La 0.9 Ce 0.1 (Fe 0.99 Mn 0.01 ) 11.6 Si 1.4 H 1.6 compound WANG Chaolun ( ), LONG Yi ( ), MA Tao ( ), ZHANG Hu ( ) (School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China) Received 12 October 2010; revised 20 December 2010 Abstract: Magnetocaloric effect and magnetic properties of La 0.9 Ce 0.1 (Fe 0.99 Mn 0.01 ) 11.6 Si 1.4 and its hydride La 0.9 Ce 0.1 (Fe 0.99 Mn 0.01 ) 11.6 Si 1.4 H 1.6 were investigated. The Curie temperature of La 0.9 Ce 0.1 (Fe 0.99 Mn 0.01 ) 11.6 Si 1.4 was increased by hydrogen absorption. XRD patterns showed that the structure of La 0.9 Ce 0.1 (Fe 0.99 Mn 0.01 ) 11.6 Si 1.4 H 1.6 remained NaZn 13 -type. The Curie temperature (T C ) of the sample was increased from 174 K to 331 K. The homogeneity of the hydrogen absorption for La 0.9 Ce 0.1 (Fe 0.99 Mn 0.01 ) 11.6 Si 1.4 H 1.6 was proven very well by the random measurement of DSC. The magnetic entropy ǻS M of La 0.9 Ce 0.1 (Fe 0.99 Mn 0.01 ) 11.6 Si 1.4 H 1.6 had peak at 326 K. The peak value of | ǻS M | was 12.3 and 7.8 J/(kg·K) under magnetic field change of 0–2 T and 0–1 T, respectively, which was comparable with Gd 5 Si 2 Ge 2 . The negative slope and inflection point of the Arrott curve indicated that the first-order magnetic transition of La 0.9 Ce 0.1 (Fe 0.99 Mn 0.01 ) 11.6 Si 1.4 was reserved after hydrogen absorption. Keywords: homogeneity of hydrogen absorption; magnetocaloric effect; magnetic entropy change; rare earths Magnetic refrigeration has been paid much attention in recent years due to its high energy efficiency and being en- vironment friendly, in contrast to the traditional gas-com- pression refrigeration technology [1–4] . The low price of raw material and high magnetic entropy change (ǻS M ) make La(FeSi) 13 a competitive candidate for the magnetic refrig- erants. However, it is hard to apply La(FeSi) 13 to room- temperature refrigerators directly due to the lower Curie temperature (T C , 190 K) of the compound [5,6] . It has been re- ported that doping H could increase T C with keeping a rela- tively high ǻS M [7–9] . Fujieda et al. [10] reported that for La(Fe 0.88 Si 0.12 ) 13 H y , the maximum concentration of hydrogen y was determined to be 1.6, and the value of T C was in- creased up to 336 K. Also, experiment shows that the con- centration of hydrogen absorption is difficult to control. When the absorption of hydrogen is below saturation, inho- mogeneity of hydrogenation in each grain will cause distri- bution of T C , resulting in broadening of ǻS M -T curve. When the hydrogen absorption is saturated, it is easy to get uniform T C . But the T C of La(FeSi) 13 compounds is higher than room temperature [10] . So it is necessary to find some substitution elements, by introducing the substitution elements in La(FeSi) 13 compounds, to adjust Curie temperature of the hydrides to room temperature. Some hydrides such as La(Fe 1–x Mn x ) 11.7 Si 1.3 H y , La 0.5 Pr 0.5 (Fe 0.88 Si 0.12 ) 13 H 1.6 have been studied. It has been reported that the substitution of Ce for La could enhance ǻS M , and decrease T C [11,12] . What’s more, T C could significantly decrease by replacing Fe with Mn but ǻS M is weakened at the same time [13,14] . According to Wang Fang’s work, with increasing Mn concentration from 0 to 0.03, the Curie temperatures of La(Fe 1íx Mn x ) 11.7 Si 1.3 de- creases from 188 to 127 K, and ǻS M of the compounds de- crease from 26.0 to 17.1 J/(kg·K) [14] . And Fujieda et al. [15] pointed out that the La 1íz Ce z (Fe xíy Mn y Si 1íx ) 13 compounds exhibit strong magnetocaloric effects in relatively low mag- netic ｿelds in a wide range of temperatures between about 19 and 180 K. In the present work, the magnetic properties of La 0.9 Ce 0.1 (Fe 0.99 Mn 0.01 ) 11.6 Si 1.4 and its hydride were studied. The homogeneity and magnetocaloric effect of the hydride were also investigated. 1 Experimental The samples with nominal composition La 0.9 Ce 0.1 (Fe 0.99 Mn 0.01 ) 11.6 Si 1.4 was prepared by arc melting. The purity of the raw materials is better than 99.9 wt.%. The mass loss for each sample is less than 0.5%. The ingot was subsequently homogenized in a vacuum sealed quartz tube at 1293 K for 15 d, and then quenched in the ice water. Hydrogen absorption took place in a tube furnace. The bulk ingot was crushed into particles with the size less than 0.18 mm before hydrogena- tion. The sample was activated at 773 K in vacuum, and then kept at 773 K for 3 h under 0.5 MPa hydrogen atmosphere. The amount of hydrogen absorption is 1.6 estimated by weight-measurement method, which equals to the maximum concentration of hydrogen in La(Fe 0.88 Si 0.12 ) 13 H y [10] . Crystal- lographic structure of the parent sample and the hydride was identified by X-ray diffraction (XRD), and the magnetic