Phase, structural, and magnetocaloric properties of high temperature annealed LaFe11.6Si1.4BX

The phase relation, microstructural, hysteresis, Curie temperature, and magnetocaloric effects of LaFe11.6Si1.4Bx (x = 0.1, 0.2, 0.3, 0.4, and 0.5) prepared by arc-melting and then annealed at 1373 K (1.5 h) + 1523 K (5 h) were investigated. It was found that the main phase is NaZn13-type phase, the impurity phases include α-Fe, Fe2B, and small amount of La5Si3. The boron atom can dissolve into the crystal lattice of LaFe11.6Si1.4Bx to form interstitial solid solution, but the content of solid solution is not up to x = 0.5. For LaFe11.6Si1.4Bx (x = 0.1, 0.3, and 0.5) compounds, the Curie temperature TC increases from 190.6 to 198.3 K with the increasing of B content from x = 0.1 to 0.5. The first order magnetic transition behavior becomes weaker and magnetic entropy change ΔSM (T, H) drops with the increasing of B content, respectively. However, ΔSM (T, H) still remains a large value, 11.18 J/kg K, when x reaches to 0.5 at 0–2 T. An attractive feature is that both thermal and magnetic hysteresis can be reduced remarkably by introducing B. The maximum magnetic hysteresis loss near TC drops from 22.52 to 4.95 J/kg when the content of B increases from x = 0.1 to 0.5.

Research highlights▶ The boron atom can dissolve into the crystal lattice of LaFe11.6Si1.4Bx to form interstitial solid solution, but the content of solid solution is not up to x = 0.5. The superfluous B atoms react to Fe atoms to form Fe2B phase, thus with the increase of B content from x = 0.1 to 0.5, the Fe2B phase also increase. This result is different to some previous studies, which showed that the content of B atoms dissolving into the lattice or substitute other atoms to form interstitial solid solution is large in La(Fe, Si)13Bx. ▶ The LaFe11.6Si1.4Bx (x = 0.1, 0.2, 0.3, 0.4, and 0.5) compounds were prepared by arc-melting and annealed at 1373 K (1.5 h) + 1523 K (5 h) in this paper. The samples consist of the cubic NaZn13-type phase mainly and small amount impurity phases consisting of α-Fe, Fe2B, and very small amount of La5Si3 phase. This result is accord with some previous La(Fe,Si)13Bx compounds prepared by long time annealing. ▶ The influence of B introduced as interstitial atoms in LaFe11.6Si1.4Bx (x = 0.1, 0.2, 0.3, 0.4, and 0.5) compounds was discussed in detail. It included the phase relation, microstructural, the Curie temperature TC, magnetic and thermal hysteresis, magnetic transition behavior, and magnetocaloric effects.