Magnetic phase diagram for the mixed-valence Eu oxide ${\mathrm{EuTi}}_{1-x}{\mathrm{Al}}_x{\mathrm{O}}_3$ $\left(0\le x\le 1\right)$

We have investigated the magnetic properties of ${\mathrm{EuTi}}_{1-x}{\mathrm{Al}}_x{\mathrm{O}}_3$ with $0\le x\le 1$ and established a detailed magnetic phase diagram. Substitution of ${\mathrm{Ti}}^{4+}$ with ${\mathrm{Al}}^{3+}$, which oxidizes magnetic ${\mathrm{Eu}}^{2+}$ $\left(J=7/2\right)$ into nonmagnetic ${\mathrm{Eu}}^{3+}$ $\left(J=0\right)$, turns the antiferromagnetic insulating ground state $\left(x=0\right)$ into the ferromagnetic (FM) insulating one $\left(0.10\le x\le 0.50\right)$. The ${\mathrm{Eu}}^{2+}/{\mathrm{Eu}}^{3+}$ mixed valence is indispensable for the FM behavior. In $0.10\le x\le 0.33$, the Curie temperature $T_{\mathrm{C}}$ has a plateau at $\sim 4$ K, and the FM correlation is most enhanced around $x=0.25$. In $0.33\le x\le 1,{\mathrm{Al}}^{3+}$ substitution suppresses the FM correlation due to the dilution of magnetic ${\mathrm{Eu}}^{2+}$ ions. Our present results would provide useful information for magnetoelectric phase control of ${\mathrm{EuTiO}}_3$-based compounds.

Figure 1

Powder x-ray-diffraction profiles for ${\mathrm{EuTi}}_{1-x}{\mathrm{Al}}_x{\mathrm{O}}_3$ with (a) $0\le x\le 0.25$ and (b) $0.33\le x\le 1$ at room temperature. (c) Simulated powder XRD profiles for the end members, ${\mathrm{EuTiO}}_3$ (ETAO with $x=0)$ and ${\mathrm{EuAlO}}_3$ (ETAO with $x=1)$.

Figure 2

Temperature $\left(T\right)$ dependence of magnetization $\left(M\right)$ of (a) ETAO with $0\le x\le 0.25$ and (b) $0.25\le x\le 1$ measured at $H=100$ Oe. ZFC and FC denote zero-field cooling and field cooling, respectively. (c) $T$ dependence of magnetic susceptibility $\left(\chi \right)$ of ETAO with $x=1$ (i.e., ${\mathrm{EuAlO}}_3)$ measured at $H=100$ Oe.

Figure 3

(a) Real component ${\chi }^{\prime }$ and (b) imaginary component ${\chi }^{\prime \prime }$ of ac $\chi$ for ETAO with $0.10\le x\le 1$ measured at frequency $f=1\mathrm{Hz}$ and field amplitude $h=3\mathrm{Oe}$.

Figure 4

(a) Magnetic field $\left(H\right)$ dependence of $M$ for ETAO with $0\le x\le 0.75$ at 2 K. (b) $x$ dependence of $M_{\mathrm{sat}}$ for ETAO with $0\le x\le 1$. $M_{\mathrm{sat}}$ represents $M$ at $H=50$ kOe. (c) $H$ dependence of $M/M_{\mathrm{sat}}$ for ETAO with $0\le x\le 0.75$ at 2 K.

Figure 5

The magnetic phase diagram for ETAO. Closed circles, triangles, and open circles represent Curie temperature $T_{\mathrm{C}}$, Néel temperature $T_{\mathrm{N}}$, and Curie-Weiss temperature ${\theta }_{\mathrm{CW}}$, respectively.