Diluted ferromagnetic semiconductor Li(Zn,Mn)P with decoupled charge and spin doping

We report the discovery of a diluted magnetic semiconductor, Li(Zn,Mn)P, in which charge and spin are introduced independently via lithium off-stoichiometry and the isovalent substitution of Mn${}^{2+}$ for Zn${}^{2+}$, respectively. Isostructural to (Ga,Mn)As, Li(Zn,Mn)P was found to be a $p$-type ferromagnetic semiconductor with excess lithium providing charge doping. First-principles calculations indicate that excess Li is favored to partially occupy the Zn site, leading to hole doping. Ferromagnetism with Curie temperature up to 34 K is achieved while the system still shows semiconducting transport behavior.

Figure 1

(a) Crystal structure of LiZnP showing [ZnP${}_4$] tetrahedral coordination. (b) Lattice constants of Li${}_{1+y}$ZnP, Li${}_{1.02}$Zn${}_{1-x}$Mn${}_x$P, and Li${}_{1.04}$Zn${}_{1-x}$Mn${}_x$P for various Li and Mn concentrations. The systematic change of lattice parameters indicates the successful substation of the elements.

Figure 2

dc-magnetization measurements of Li(Zn,Mn)P systems. (a) $M$($T$) curves in ZFC and FC modes with $H$ $=$ 100 Oe for Li${}_{1.04}$(Zn${}_{1-x}$Mn${}_x$)P specimens (no visible difference between ZFC and FC procedures for small coercive fields). Inset shows the temperature dependence of the inverse susceptibility. (b) Top: $T_C$ and θ for Li${}_{1+y}$Zn${}_{1-x}$Mn${}_x$P. Bottom: $M_{\mathrm{eff}}$ and $M_{\mathrm{sat}}$ for Li${}_{1.04}$Zn${}_{1-x}$Mn${}_x$P. Dashed lines indicate extrapolation. (c) $M$($H$) and ρ($H$) in Li${}_{1.04}$Zn${}_{0.9}$Mn${}_{0.1}$P show hysteresis, demonstrating ferromagnetism with a small coercive field of about 50 Oe.

Figure 3

(a) ρ($T$) and the inverse carrier concentration for Li${}_{1.04}$Zn${}_{0.9}$Mn${}_{0.1}$P. Inset shows Hall resistivity of Li${}_{1.04}$Zn${}_{0.9}$Mn${}_{0.1}$P, exhibiting $p$-type carriers with $n_p$ $=$ 6.1 × 10${}^{16}$ cm${}^{-3}$, 1.82 × 10${}^{17}$ cm${}^{-3}$, and 3.27 × 10${}^{17}$ cm${}^{-3}$ at 100, 200, and 300 K, respectively. (b) Correlation between $T_C$ and the hole concentration for four types of tetrahedrally coordinated DMS systems. It exhibits a large difference between Li(Zn,Mn)P and other tetrahedrally coordinated systems. The blue stars represent (In,Mn)As films with electric-field controlled hole concentration. (c) Magnetoresistivity ${\rho }_H$($T$) of Li${}_{1.04}$Zn${}_{0.9}$Mn${}_{0.1}$P under various field strengths. Inset shows negative magnetoresistance at low temperature.