Colossal positive magnetoresistance in a doped nearly magnetic semiconductor

We report on a positive colossal magnetoresistance (MR) induced by metallization of $\mathrm{Fe}{\mathrm{Sb}}_2$, a nearly magnetic or “Kondo” semiconductor with $3d$ ions. We discuss the contribution of orbital MR and quantum interference to the enhanced magnetic field response of electrical resistivity.

Figure 1

(a) Electrical transport properties of ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{\mathrm{Sb}}_2$ dramatically change with a small change in shoichiometry. The sample with $x=0.1$ manifests the lowest resistivity. With further Co substitution, we see a gradual increase in residual resistivity. (b) Temperature dependence of magnetoresistance $\mathrm{MR}=[\rho \left(90\mathrm{kOe}\right)-\rho \left(0\right)]∕\rho \left(0\right)$ in doped ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{\mathrm{Sb}}_2$ semiconductor alloys for $x=0–0.4$. CMR is observed for all $x$. (c) Resistivity isotherms of ${\mathrm{Fe}}_{0.9}{\mathrm{Co}}_{0.1}{\mathrm{Sb}}_2$ up to $350\mathrm{kOe}$. Resistivity increases 3 orders of magnitude (103 100%) at $1.8\mathrm{K}$.

Figure 2

Hall resistivity versus magnetic field. Solid lines are the fits when magnetization $M$ is taken into account.

Figure 3

(a) Hall constant $R_H={\rho }_{xy}∕H$ of $\mathrm{Fe}{\mathrm{Sb}}_2$ is well described by a two-carrier model. [(b)–(d)] For ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{\mathrm{Sb}}_2$ $(0.1⩽x⩽0.4)$, the fits of the two carrier model to experimental data are rather unsatisfactory since it cannot account for maxima and minima in $R_H\left(H\right)$. Co substitution in ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{\mathrm{Sb}}_2$ fills energy bands that are not involved in thermal excitation of carriers across the gap in $\mathrm{Fe}{\mathrm{Sb}}_2$. $R_H$ shows an excellent agreement with the three-carrier model for all $x$; selected data are shown for clarity. Solid lines are fits to the multicarrier model.

Figure 4

Magnetoresistance calculated according to the multicarrier model for ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{\mathrm{Sb}}_2$ in $90\mathrm{kOe}$ shown in the low plot as linked symbols, compared to the observed MR shown as the scattered symbols.

Figure 5

(a) Magnetoconductivity of ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{\mathrm{Sb}}_2$. Conductivity change $\Delta \sigma =\sigma (H,T)-\sigma (H,0)$, with $\sigma (H,0)$ determined from fits of data to a $T^{1∕2}$ dependence at $H=90\mathrm{kOe}$. (b) Quasi-1D weak localization fits to MR at $T=1.8\mathrm{K}$ for ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{\mathrm{Sb}}_2$. Data for $x=0$ are shown at $T=100\mathrm{K}$ in the metallic quasi-1D regime of the $\widehat{b}$-axis conductivity.