Influence of Cobalt Substitution on the Magnetic Properties of Fe₅PB₂

Abstract

The substitutional effects of cobalt in (FeCo)PB have been studied with respect to crystalline structure and chemical order with X-ray diffraction and Mössbauer spectroscopy. The magnetic properties have been determined from magnetic measurements, and density functional theory calculations have been performed for the magnetic properties of both the end compounds, as well as the chemically disordered intermediate compounds. The crystal structure of (FeCo)PB is tetragonal (space group I4/mcm) with two different metal sites, with a preference for cobalt atoms in the M(2) position (4c) at higher cobalt contents. The substitution also affects the magnetic properties with a decrease of the Curie temperature (T) with increasing cobalt content, from 622 to 152 K for FePB and (FeCo)PB, respectively. Thus, the Curie temperature is dependent on composition, and it is possible to tune T to a temperature near room temperature, which is one prerequisite for magnetic cooling materials.

Chemical order or disorder – a theoretical stability expose for expanding the compositional space of quaternary metal borides

“…All five experimentally reported solid solutions () 5 AB 2 are predicted to be stable here, 35,36,56 as well as the recently discovered Ti 4 MoSiB 2 o -MAB. 37 Noteworthily, the additional 121 solid solution and 35 o -MAB phases are predicted to be stable, mainly for A = Si, P, and Ge, suggesting that metal alloying in T2 phases is a prospective path towards expanding the possible chemistries which, in turn, provide a high tunning potential of these materials.…”

“…For the solid solution () 5 AB 2 we evaluate Δ G solid solution at 2000 K, motivated by a typical temperature of 1000 to 1900 °C (1273 to 2173 K) used for the synthesis of M 5 AB 2 ( e.g. M = Mo, W, Mn) and (Fe 0.8 ) 5 AB 2 (M′′ = Mn, Co), 35,36,56,57 by including the contribution of configurational entropy to Gibb's free energy, using eqn (3) and (4). The depicted symbol thus represents the chemical order of the lowest energy at 2000 K; filled squares for ordered M′′AB 2 o -MAB and open circles for the solid solution () 5 AB 2 .…”

“…For the solid solution (M 0 0:8 M 00 0:2 ) 5 AB 2 we evaluate DG solid solution at 2000 K, motivated by a typical temperature of 1000 to 1900 1C (1273 to 2173 K) used for the synthesis of M 5 AB 2 (e.g. M = Mo, W, Mn) and (Fe 0.8 M 00 0:2 ) 5 AB 2 (M 00 = Mn, Co), 35,36,56,57 by including the contribution of configurational entropy to Gibb's free energy, using eqn (3) and ( 4 All five experimentally reported solid solutions (M 0 0:8 M 00 0:2 ) 5 AB 2 are predicted to be stable here, 35,36,56 as well as the recently discovered Ti 4 MoSiB 2 o-MAB. 37 Noteworthily, the additional 121 solid solution and 35 o-MAB phases are predicted to be stable, mainly for A = Si, P, and Ge, suggesting that metal alloying in T2 phases is a prospective path towards expanding the possible chemistries which, in turn, provide a high tunning potential of these materials.…”

“…DG solid solution o DH o-MAB (Fe 0.8 Co 0.2 ) 5 AB 2 (A = Si, P) 35,36,56 (Ti 0.8 W 0.2 ) 5 AB 2 (A = Si, P) (Co 0.8 Fe 0.2 ) 5 AB 2 (A = P) 35 (V 0.8 Ti 0.2 ) 5 AB 2 (A = Si, P) (V 0.8 M 00 0:2 ) 5 AB 2 (A = Si, P, Ge; M 00 = Nb, Ta, Mn) (V 0.8 M 00 0:2 ) 5 AB 2 (A = Si, P, Ga, Ge; M 00 = Cr, Mo, W) (V 0.8 Fe 0.…”

“…T2 phases are attractive due to their high oxidation resistance, 30 nearly isotropic thermal expansion, 31 superconducting properties 32,33 and potential for use as rare-earth free permanent magnets. 34–36…”