AlFe_2–xCo_xB₂ (x = 0–0.30): T_C Tuning through Co Substitution for a Promising Magnetocaloric Material Realized by Spark Plasma Sintering

Abstract

AlFeB and AlFeCoB (x = 0-0.30) were synthesized from the elements in three different ways. The samples were characterized by powder X-ray diffraction, Rietveld refinements, energy-dispersive X-ray spectroscopy, and magnetic measurements. Using Al flux the formation of AlFeB single crystals is preferred. Arc melting enables the substitution of ∼6% Co. This substitution of Fe by Co decreases the Curie temperature T from 290 to 240 K. The highest Co substitution up to 15% is achieved by spark plasma sintering (SPS). T is reduced to 205 K. In all cases an excess of Al is necessary to avoid the formation of ferromagnetic FeB. AlFeCo is the common byproduct. T and the cobalt content are linearly correlated. The transition paramagnetic-ferromagnetic remains sharp for all examples. The magnetic entropy change of the Co-containing samples is comparable to AlFeB. SPS synthesis yields, in short reaction times, a homogeneous and dense material with small amounts of paramagnetic AlFeCo as an impurity, which can serve as sinter additive. These properties make AlFeCoB a promising magnetocaloric material for applications between room temperature and 200 K.

Magnetic and mechanical effects of Mn substitutions in AlFe2B2

“…This was confirmed using neutron diffraction where a canted antiferromagnetic ordering (below 390 K) was found with the magnetic moments oriented either between the a or c-axes with a doubling of the crystallographic unit cell in the c-direction [22]. By substituting iron on the transition metal site in AlFe 2 B 2 with cobalt, the T C decreases linearly with increasing cobalt concentration, down to 205 K for 30% substitution [23]. ∆S mag did not, however, change significantly with the substitution.…”

Magnetic properties of single crystalline itinerant ferromagnet AlFe2B2

“…A Mössbauer study on arc-melted and annealed sample has reported the Curie temperature of 300 K [2]. At the lower limit, the Curie temperature of spark plasma sintered AlFe 2 B 2 was reported to be 274 K [7]. The reported saturation magnetic moment also manifests up to 25% variation from the theoretically predicted saturation moment of 1.25 µ B /Fe.…”

A Delicate Balance between Antiferromagnetism and Ferromagnetism: Theoretical and Experimental Studies of A2MRu5B2 (A=Zr, Hf; M=Fe, Mn) Metal Borides

“…[18] Te tragonal Ti 3 Co 5 B 2 (space group P4/mbm,n o. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] The crystal structure of the ternary variants is formed by face-connected trigonal, tetragonal, andp entagonal prisms of T/T'-atoms (electron-rich transition metals such as Co, Rh, Ir,R u). [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] The crystal structure of the ternary variants is formed by face-connected trigonal, tetragonal, andp entagonal prisms of T/T'-atoms (electron-rich transition metals such as Co, Rh, Ir,R u).…”