Magnetocaloric effect of nonstoichiometric La1−xFe11.4+xSi1.6 alloys with first-order and second-order magnetic transitions. (August 2015)

• Record Type: Journal Article
• Authors: Lai, J.W.; Zheng, Z.G.; Zhong, X.C.; Montemayor, R.; Liu, Z.W.; Zeng, D.C.
• Is Part Of: Intermetallics. Volume 63(2015:Aug.)
• Page Start: 7
• Page End: 11
• Publication Date: 2015-08
• Subjects: A. Functional alloys -- B. Magnetic properties -- B. Phase transformation -- D. Microstructure -- G. Energy systems; Intermetallic compounds -- Metallography -- Periodicals; Metallic glasses -- Periodicals; Composés intermétalliques -- Métallographie -- Périodiques; 669.94
• DOI: 10.1016/j.intermet.2015.03.012
• Languages: English
• ISSNs: 0966-9795

Abstract

Abstract: Variation from a first-order magnetoelastic transition (FOMT) to a second-order magnetic transition (SOMT) could be controlled by finely adjusting the Fe/La ratio in the non-stoichiometric La1− x Fe11.4+ x Si1.6 ( x = 0, 0.05, 0.10, 0.15 and 0.20) alloys. Particularly, a nearly stoichiometric ratio of NaZn 13 -type phase was obtained with an addition of excess 0.15 at% Fe. When x value increased from 0 to 0.20, the Curie temperature ( T C ) increased from 198.6 to 216.6 K due to lattice shrinkage and the magnetic entropy change (−Δ S M ) decreased from 18.4 to 8.0 J/(kg·K) (at 0−2 T) and from 22.5 to 13.8 J/(kg·K) (at 0−5 T), which may be ascribed to the change from the itinerant-electron metamagnetism (IEM) to second order magnetic transition. Thus their effective refrigeration capacities declined from 347.6 to 245.9 J kg −1 under 0–5 T, which values were comparable to the Gd5 Si2 Ge1.9 Fe0.1 . The Fe/La ratio in NaZn13 -phase was possibly dominant to induce the transition from first to second order among La1− x Fe11.4+ x Si1.6 alloys. The thermal hysteresis decreased by 87% to 0.3 K and magnetic hysteresis losses reduced by 90% to 1.4 J kg −1 under 0–5 T. Near the transition border, the alloys with x = 0.15 produced a giant magnetocaloric effect of about 11.8 J/(kg·K) under 0–2 T at T C = 205.6 K. The magnetic hysteresis was 3.01 J kg −1 and the thermal hysteresis was 1.9 K. The material near the border of transition could be suitable for future magnetic refrigeration application. Highlights: Extra Fe needs to be added to achieve the 1:13 stoichiometry in NaZn13 -type phase. When increasing Fe, T C arises to lower room temperature range, 198.6 K–216.6 K. With Fe rising, ΔS M declines significantly from 18.4 to 8.0 J/(kg·K) under 0–2 T. The thermal hysteresis decreased by 87% while magnetic hysteresis reduced by 90%. Fe/La ratio in NaZn13 possibly induced the transition from first to second order.