Magnetic frustration and magnetocaloric effect in AlFe2−x Mn x B2 (x = 0–0.5) ribbons.

The crystal structure and magnetic properties of AlFe_2−xMn_xB₂ (x = 0–0.5) compounds were investigated. With increasing Mn content, the magnetic properties of these compounds evolve gradually and the lattice parameters change continuously: Curie temperature (T_c) decreases from 312 K (x = 0) to 220 K (x = 0.5) and a new phase transition from the ferromagnetic state (FM) to spin-glass state (SPG) appears upon cooling. The lattice shrinks in the ab plane while it expands in the c direction. The formation of re-entrant SPG around 50 K was studied via temperature dependent ac and dc magnetization as well as the initial magnetization curves in 5 K. The reason for this glass state is the triangular configuration of magnetic atoms and the antiferromagnetic interactions introduced by Mn substitutions. The Curie transition leads to a conventional magnetocaloric effect (MCE). The Mn doping leads to a decrease in the MCE near room temperature, but there is a plane in entropy change (ΔS) for the x = 0.1 compound under low field which makes these compounds good candidates to produce composites used for magnetic refrigeration application in a wide temperature span. [ABSTRACT FROM AUTHOR]