Magnetic Properties of Ga$_{1-x}$Mn$_{x}$ P-based Quaternary Ferromagnetic Semiconductors

Ga$_{1-x}$Mn$_{x}$P is a ferromagnetic semiconductor in which exchange is mediated by carriers localized in a Mn-derived impurity band [Scarpulla \textit{et al.}, Phys. Rev. Lett. \textbf{95} 207204 (2005)]. Despite its non-metallic nature even for x$\sim $0.042, Ga$_{1-x}$Mn$_{x}$P displays many properties that are not significantly different from those of the canonical system Ga$_{1-x}$Mn$_{x}$As including an approximately linear increase of the Curie temperature (T$_{C})$ with x and a strong spin polarization of the density of states at the Fermi energy. Here we report the effect of partial anion replacement by either S or As on the magnetic properties of Ga$_{1-x}$Mn$_{x}$P-based thin films. In Ga$_{1-x}$Mn$_{x}$P$_{1-y}$S$_{y}$ both T$_{C}$ and X-ray magnetic circular dichroism decrease monotonically with y due to compensation of ferromagnetism-mediated holes by electrons introduced by S donors. Addition of sulfur significantly enhances the uniaxial magnetic anisotropy between in-plane $<$110$>$-type directions with increasingly harder [110] axes as y increases. Finally, we explore Ga$_{1-x}$Mn$_{x}$As$_{1-y}$P$_{y}$ for which it has been predicted [Masek \textit{et al}. cond-mat/0609158v1] that T$_{C}$ will increase as y increases, thus providing a route to higher T$_{C}$ based on the well-studied Ga$_{1-x}$Mn$_{x}$As system.