Magnetic phase inLaFe11.4Al1.6with very low interstitial carbon content

Abstract

${\mathrm{NaZn}}_{13}$-type ${\mathrm{LaFe}}_{11.4}{\mathrm{Al}}_{1.6}{\mathrm{C}}_{\ensuremath{\delta}}$ $(\ensuremath{\delta}=0\ensuremath{-}0.08)$ compounds were prepared by arc melting. At low temperature, the ground state is antiferromagnetic and ferromagnetic for $\ensuremath{\delta}=0$ and 0.04, respectively. Although the ground state remains antiferromagnetic for $\ensuremath{\delta}=0.02$, the ferromagnetic state can be induced by a magnetic field at about $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. During the transition between antiferromagnetic and ferromagnetic states, the magnetization exhibits a sharp discontinuity, indicating the formation of a homogeneous phase by intersitial carbon in spite of the very small $\ensuremath{\delta}$. The transition from low-temperature antiferromagnetic state (AFI) to ferromagnetic state induced by a magnetic field is irreversible. On the contrary, the transition from high-temperature antiferromagnetic state (AFII) to ferromagnetic state is reversible. Considering the magnetization behaviors and the variation of heat capacity with temperature, we can deduce that the AFI is different from the AFII.