Effect of pressure on the magnetic, transport, and thermal-transport properties of the electron-doped manganite ${\mathrm{CaMn}}_{1-x}{\mathrm{Sb}}_x{\mathrm{O}}_3$

We have demonstrated the effect of hydrostatic pressure on magnetic and transport properties, and thermal-transport properties in the electron-doped manganite ${\mathrm{CaMn}}_{1-x}{\mathrm{Sb}}_x{\mathrm{O}}_3$. The substitution of Sb${}^{5+}$ ion for Mn ${}^{4+}$ site of the parent matrix causes one-electron doping with the chemical formula ${\mathrm{CaMn}}_{1-2x}^{4+}{\mathrm{Mn}}_x^{3+}{\mathrm{Sb}}_x^{5+}{\mathrm{O}}_3$ accompanied by a monotonous increase in unit-cell volume as a function of $x$. Upon increasing the doping level of Sb, the magnitudes of both electrical resistivity and negative Seebeck coefficient are suppressed at high temperatures, indicating the electron doping. Anomalous diamagnetic behaviors at $x=0.05$ and 0.08 are clearly observed in the field cooled dc magnetization. The effect of hydrostatic pressure on dc magnetization is in contrast to the chemical pressure effect due to Sb doping. The dynamical effect of ac magnetic susceptibility measurement points to the formation of the magnetically frustrated clusters such as FM clusters embedded in canted AFM matrix.

Figure 1

(a) X-ray diffraction patterns of CaMn${}_{1-x}$Sb${}_x$O${}_3$ ($x=0.02$, 0.05, 0.08, and 0.1) taken at room temperature. Cross marks denote intensity peaks of orthorhombic CaMnO${}_3$. (b) The lattice parameters and unit-cell volume as a function of Sb contents from 0.02 up to 0.1.

Figure 2

(a) Temperature variation of electrical resistivity $\rho$ for the CaMn${}_{1-x}$Sb${}_x$O${}_3$ system ($x=0.02$, 0.05, 0.08, and 0.1). For comparison, the data of the parent compound are presented. (b) The $\rho$-$T$ plot is magnified between 180 K and room temperature. The solid lines denote the fits of the high-$T$ data by using a small polaron model. The activation energy $W$ is listed as a function of the Sb content in Table . (c) Magnetoresistance effect, $\mathit{MR}=[R(H)-R(0)]/R(0)\times 100\%$ at 20 K for the CaMn${}_{1-x}$Sb${}_x$O${}_3$ system ($x=0.02$, 0.05, and 0.08).

Figure 3

(a) Temperature variation of electrical resistivity $\rho$ for the CaMn${}_{1-x}$Sb${}_x$O${}_3$ system ($x=0.02$ and 0.08) at an applied pressure of 0.8 GPa. For comparison, the data at ambient pressure are presented. (b) $\Delta R/R=[R(T,0.8$ GPa$)-R(T,0$ GPa$)]/R(T,0$ GPa) $\times 100\%$ for the CaMn${}_{1-x}$Sb${}_x$O${}_3$ system ($x=0.02$, 0.05, and 0.08). The inset displays $\Delta R/R$ as a function of Sb content at 100 K and 300 K.

Figure 4

(a) Temperature variation of Seebeck coefficient $S$ for the CaMn${}_{1-x}$Sb${}_x$O${}_3$ system ($x=0.02$, 0.05, 0.08, and 0.1). The solid lines denote the $T$ linear fits to the $S(T)$ data in the temperature region above 130 K. The arrows denote the magnetic transition temperatures determined from the magnetization data. (b) Thermal conductivity $\kappa$ of CaMn${}_{1-x}$Sb${}_x$O${}_3$ ($x=0$, 0.02, 0.05, 0.08, and 0.1). For comparison, the $\kappa$ data of the parent compound CaMnO${}_3$ are presented. The inset also represents the $S$ data of parent CaMnO${}_3$.

Figure 5

Temperature dependence of zero-field-cooled and field-cooled magnetization of the Sb substituted CaMn${}_{1-x}$Sb${}_x$O${}_3$ recorded at $H=$10 mT. In the case of ambient pressure, (a) $x=0.02$, (c) $x=0.05$, and (e) $x=0.08$. In the case of 0.8 GPa, (b) $x=0.02$, (d) $x=0.05$, and (f) $x=0.08$. For comparison, the ZFC data of the parent sample are given in (a). In the inset of (e), the $M-T$ curve with the $x=0.1$ sample is presented at 0 GPa.

Figure 6

ZFC and FC magnetization curves of the Sb substituted CaMn${}_{1-x}$Sb${}_x$O${}_3$ ($x=0.02$, 0.05, and 0.08) collected at $H=50$ mT. For ambient pressure, we get (a) $x=0.02$, (c) $x=0.05$, and (e) $x=0.08$. For applied pressure of 0.8 GPa, (b) $x=0.02$, (d) $x=0.05$, and (f) $x=0.08$.

Figure 7

(a) Temperature dependence of ZFC and FC magnetization curves of the CaMn${}_{1-x}$Sb${}_x$O${}_3$ ($x=0.02$ and $0.05$) samples under an applied field of 1.5 T. (b) Magnetization curves $M$ vs $H$ of $x=0.02$, 0.05, and 0.08 at 5 K.

Figure 8

The real part ${\chi }^{\prime }$ of ac magnetic susceptibility of CaMn${}_{1-x}$Sb${}_x$O${}_3$ collected at zero dc magnetic field with frequency ranging from 1 Hz to 1000 Hz. (a) $x=0.02$, (b) $x=0.05$, and (c) $x=0.08$. The amplitude of the ac magnetic field $H_{\mathrm{ac}}$ was set to be 0.5 mT. The arrows point to the direction of increasing frequencies.

Figure 9

The imaginary part ${\chi }^{″}$ of the ac magnetic susceptibility of CaMn${}_{1-x}$Sb${}_x$O${}_3$ as a function of frequency varying from 1 Hz to 1000 Hz at $H_{\mathrm{dc}}$ $=$ 0 T ($H_{\mathrm{ac}}$ $=$ 0.5 mT). (a) $x=0.02$, (b) $x=0.05$, and (c) $x=0.08$.

Figure 10

The real and imaginary parts of ac magnetic susceptibility of CaMn${}_{1-x}$Sb${}_x$O${}_3$ measured at 10 Hz under a superimposed dc field ($H_{\mathrm{dc}}$ $=$ 10 mT). For $x=0.02$, (a) ${\chi }^{\prime }$ and (b) ${\chi }^{″}$. For $x=0.05$, (c) ${\chi }^{\prime }$ and (d) ${\chi }^{″}$. For $x=0.08$, (e) ${\chi }^{\prime }$ and (f) ${\chi }^{″}$. The ac magnetization data are recorded as a function of temperature under ZFC and FC conditions.

Figure 11

The real and imaginary parts of ac magnetic susceptibility of CaMn${}_{0.9}$Sb${}_{0.1}$O${}_3$ a function of frequency varying from 1 Hz to 1000 Hz at $H_{\mathrm{dc}}$ $=$ 0 T ($H_{\mathrm{ac}}$ $=$ 0.5 mT). For $x=0.1$, (a) ${\chi }^{\prime }$ and (b) ${\chi }^{″}$. For comparison, the ac magnetization data recorded as a function of temperature under ZFC and FC conditions are given in (c) ($H_{\mathrm{dc}}$ $=$ 10 mT).