Spin-Reorientation, Ferroelectricity, and Magnetodielectric Effect in ${\mathrm{YFe}}_{1-x}{\mathrm{Mn}}_x{\mathrm{O}}_3(0.1\mathbf{\le }x\mathbf{\le }0.40)$

We report the observation of magnetoelectric and magnetodielectric effects at different temperatures in Mn-substituted yttrium orthoferrite, ${\mathrm{YFe}}_{1-x}{\mathrm{Mn}}_x{\mathrm{O}}_3(0.1\le x\le 0.40)$. Substitution of Mn in antiferromagnetic ${\mathrm{YFeO}}_3(T_N=640\mathrm{K})$ induces a first-order spin-reorientation transition at a temperature, $T_{\mathrm{SR}}$, which increases with $x$ whereas the Néel temperature ($T_N$) decreases. While the magnetodielectric effect occurs at $T_{\mathrm{SR}}$ and $T_N$, the ferroelectricity appears rather at low temperatures. The origin of magnetodielectric effect is attributed to spin-phonon coupling as evidenced from the temperature dependence of Raman phonon modes. The large magnetocapacitance (18% at 50 kOe) near $T_{\mathrm{SR}}=320\mathrm{K}$ and high ferroelectric transition temperature ($\sim 115\mathrm{K}$) observed for $x=0.4$ suggest routes to enhance magnetoelectric effect near room temperature for practical applications.

Figure 1

Magnetodielectric effect in ${\mathrm{YFe}}_{1-x}{\mathrm{Mn}}_x{\mathrm{O}}_3$. Dielectric constant (left axis) shows an anomaly near the reorientation transition in field cooled magnetization data (right axis) in compounds ${\mathrm{YFe}}_{0.8}{\mathrm{Mn}}_{0.2}{\mathrm{O}}_3$ (upper panel $a$) and ${\mathrm{YFe}}_{0.7}{\mathrm{Mn}}_{0.3}{\mathrm{O}}_3$ (lower panel $b$).

Figure 2

Temperature dependence of (a) field cooled magnetization data under applied field of 100 Oe and 50 kOe showing change in the spin-reorientation temperature and (b) dielectric constant at 0 T and 50 kOe revealing a magnetocapacitance effect in ${\mathrm{YFe}}_{0.6}{\mathrm{Mn}}_{0.4}{\mathrm{O}}_3$. The insets show dielectric constant anomalies near $T_{\mathrm{SR}}$ and $T_N$.

Figure 3

(a) Top panel shows frequency dependence of dielectric constant (left axis) and loss (right axis) under 100 Oe and 50 kOe at 320 K. Bottom panel (b) shows magnetocapacitance (MC) and magnetoloss (ML) against frequency. Inset shows field dependence of magnetoresistance and magnetocapacitance. Large MC and low ML values at high frequency indicate intrinsic magnetodielectric behavior.

Figure 4

Temperature dependence of ferroelectric polarization, $P$ in ${\mathrm{YFe}}_{0.6}{\mathrm{Mn}}_{0.4}{\mathrm{O}}_3$ at positive and negative poling fields confirming bipolar nature. Polarization is observed to increase with magnetic field with a corresponding decrease in the Curie temperature. Inset shows the effect of magnetic field on the ferroelectric transition temperature.

Figure 5

(a) Raman spectrum of ${\mathrm{YFe}}_{0.6}{\mathrm{Mn}}_{0.4}{\mathrm{O}}_3$ recorded at room temperature. Inset shows the deconvoluted peak centered around $640{\mathrm{cm}}^{-1}$ into $B_{2g}$ and $B_{3g}$ modes. Temperature dependence of frequency corresponding to $B_{2g}$ and $B_{3g}$ phonon modes across the (b) ferroelectric and (c) magnetic transitions (see text for details). Solid lines in (c) are guide to eye and dotted lines in (b) represent the anharmonic contributions.