From Waste-Heat Recovery to Refrigeration: Compositional Tuning of Magnetocaloric Mn_1+xSb

Abstract

Magnetic refrigeration, as well as waste-heat recovery, can be accomplished through the magnetocaloric effect, where temperature changes the magnetic state of a material or vice versa. Promising magnetocaloric materials display large changes in magnetic entropy (∆S M) upon application of a moderate magnetic field, and often associated with magnetic materials possessing some degree of magnetostructural coupling. In such compounds, the magnetic transition is coupled to some structural transition at the ordering temperature, and indicators for these are readily calculated by the magnetic deformation proxy Σ M. MnSb, with a Curie temperature T C = 577 K is has a calculated magnetic deformation of Σ M = 5.9%, and is a promising candidate material for waste-heat recovery. The temperature-dependence of structural, magnetic, and magnetocaloric properties of Mn 1+x Sb, where x is a tunable amount of interstitial Mn, are studied here. Excess Mn is incorporated as an interstitial whose magnetic moment is anti-aligned with the stoichiometric Mn, and the excess Mn has the effect of lowering T C , such that the Curie temperature can be tuned from 577 K to nearly room temperature at 318 K for x = 0.2. For x = 0.0, 0.1, and 0.2, values of ∆S M under a maximum magnetic field H = 5 T are found to be 3.65 J K −1 kg −1 , 3.00 J K −1 kg −1 , and 2.83 J K −1 kg −1 , respectively. While the maximum ∆S M decreases with x, the high refrigerant capacity-a more holistic measure of performance-is retained in this highly tunable system.

Structural changes upon magnetic ordering in magnetocaloric AlFe2B2

“…4 A survey of magnetocalorics based on density functional theory calculations has established a broad correlation between magnetostructural coupling (approximated using magnetic deformation calculations) and MCE in materials with both first-order and continuous transitions. 11,12,19,20 This work made the prediction that AlFe 2 B 2 , among some other materials with strong magnetocaloric effects observed at continuous magnetic transitions, would display strong magnetostructural coupling when investigated experimentally. AlFe 2 B 2 was first isolated and its crystal structure solved by Jeitschko in 1969.…”

Evolution of noncollinear magnetism in magnetocaloric MnPtGa

“…Often, magnetic ordering leads to expanded volume in such systems, as magnetism favors localization of the itinerant electrons [11,[29][30][31][32][33][34][35]. However, in a few cases negative volume magnetostriction has been reported, such as in the antiferromagnets MnO and MnS [36] and the magnetocalorics Mn 5 Ge 3 [37] and Mn 1+x Sb [38]. In these cases, the volume-dependence of the magnetic exchange energy is implicated as the dominant driver of the magnetostructural interaction.…”

Магнитная анизотропия игольчатых монокристаллических включений MnSb в матрице InSb

“…Антимонид марганца -ферромагнитный полуметалл с гексагональной структурой типа NiAs [1] с наибольшей среди соединений Mn−B V температурой Кюри T C ≈ 585 K [2]. Интерес к этому материалу значительно возрос в последнее время в связи с перспективностью его применения для магнитного охлаждения [3]. Также MnSb обладает сильной магнитокристаллической анизотропией (МА), а направление оси легкого намагничивания (ОЛН) меняет свою ориентацию с изменением температуры, стехиометрии [1,4] и толщины в случае тонких пленок [5], что делает его пригодным для использования в устройствах магнитной записи повышенной плотности [6].…”

“…Характер обеих кривых указывает на то, что ОЛН перпендикулярна длинной стороне игольчатых включений MnSb, т. е. их оси c. ± 0.2) • 10 6 erg/cm 3 (T = 5 K). Также были определены значения K при промежуточных температурах T = 100 и 200 K. Абсолютные значения K при T = 300 K составляли 1.2 • 10 6 и 0.4 • 10 6 erg/cm3 по данным, полученным с помощью крутильного магнитометра [1] и на основе ферромагнитного резонанса [8] соответственно. Отметим, что обсуждаемые здесь значения M S и K, а также направление ОЛН справедливы для отдельной иголки.…”