Wednesday, December 5, 2012

1212.0315 (Shen Bao-Gen et al.)

Magnetic properties and magnetocaloric effects in NaZn13-type La(Fe,
Al)13-based compounds

Shen Bao-Gen, Hu Feng-Xia, Dong Qiao-Yan, Sun Ji-Rong
In this article, our recent progresses about the effects of atomic substitution, magnetic field and temperature on the magnetic and magnetocaloric properties of the LaFe13-xAlx compounds are reviewed. With the increase of aluminum content, the compounds exhibit successively an antiferromagnetic (AFM), a ferromagnetic (FM), and a mictomagnetic state. Furthermore, the AFM coupling of LaFe13-xAlx can be converted to a FM coupling by substituting Si for Al, Co for Fe and magnetic rare-earth R for La, or introducing interstitial C or H atom. However, low doping levels lead to FM clusters embedded in AFM matrix, and the resultant compounds can undergo, under appropriate applied fields, first an AFM-FM and then a FM-AFM phase transition while heated, with significant magnetic relaxation in the vicinity of the transition temperature. The Curie temperature of LaFe13-xAlx can be shifted to room temperature by choosing appropriate contents of Co, C or H, and strong magnetocaloric effect can be obtained around the transition temperature. For example, for the LaFe11.5Al1.5C0.2H1.0 compound, the maximal entropy change reaches 13.8 J/kg K for a field change of 0-5 T, occurring around the room temperature. It is 42% higher than that of Gd and, therefore, this compound is a promising room-temperature magnetic refrigerant.
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