Magnetocaloric Effect in AlFe₂B₂: Toward Magnetic Refrigerants from Earth-Abundant Elements

Abstract

AlFe2B2 was prepared by two alternative synthetic routes, arc melting and synthesis from Ga flux. In the layered crystal structure, infinite chains of B atoms are connected by Fe atoms into two-dimensional [Fe2B2] slabs that alternate with layers of Al atoms. As expected from the theoretical analysis of electronic band structure, the compound exhibits itinerant ferromagnetism, with the ordering temperature of 307 K. The measurement of magnetocaloric effect (MCE) as a function of applied magnetic field reveals isothermal entropy changes of 4.1 J kg(-1) K(-1) at 2 T and 7.7 J kg(-1) K(-1) at 5 T. These are the largest values observed near room temperature for any metal boride and for any magnetic material of the vast 122 family of layered structures. Importantly, AlFe2B2 represents a rare case of a lightweight material prepared from earth-abundant, benign reactants which exhibits a substantial MCE while not containing any rare-earth elements.

A Simple Computational Proxy for Screening Magnetocaloric Compounds

“…For magnetic refrigeration near room temperature, several suitable materials are being studied in detail, including (Mn,Fe) 2 (P,Si), 7,8 La(Fe,Si) 13 and its hydrides, 9 and Heusler compounds. 10,11 These systems are comprised of Earth-abundant, inexpensive elements and combine large ∆S M and ∆T ad , with low hysteresis, high mechanical and chemical stability, and good thermal properties. Despite great progress within these systems, discovery of new magnetocalorics with desirable properties is still important.…”

Mössbauer study of the magnetocaloric compound AlFe2 B 2

“…In the aluminium layer the atoms occupy the 2a-position and in the (Fe 2 B 2 )-slabs iron and boron occupy the 4j and 4i positions, respectively. In previous studies, magnetic measurements and Mössbauer spectroscopy have shown that AlFe 2 B 2 is a ferromagnetic material with reported values of T c varying between 282-320 K and saturation magnetic moments ranging between 0.95 and 1.25 µ B /Fe-atom [8][9][10]. The magnetic entropy change has been reported to -4.1 and -7.7 J/K kg at an applied magnetic field of 1600 and 4000 kA/m, respectively [9].…”

Developing magnetofunctionality: Coupled structural and magnetic phase transition in AlFe2B2

“…This materials challenge has proven to be formidable; in addition to difficulties with materials fabrication, mechanical integrity and corrosion issues during cycling, many magnetothermal materials under consideration today contain rare, toxic or strategically-limited elements: these materials include Gd, Gd 5 (GeSi) 4 , FeRh, MnAs, FeMnAsP and (La((FeCo)Si(H)) 13 [4]- [7]. Against this backdrop the recent report of a room-temperature magnetocaloric effect in the ferromagnetic compound AlFe 2 B 2 is of interest [8]. This intermetallic compound is comprised entirely of non-critical, easily accessible, stable and easily recyclable elements.…”