Multiglass properties and magnetoelectric coupling in the uniaxial anisotropic spin-cluster-glass ${\mathrm{Fe}}_2\mathrm{Ti}{\mathrm{O}}_5$

The compound ${\mathrm{Fe}}_2\mathrm{Ti}{\mathrm{O}}_5$ (FTO) is a well-known uniaxial anisotropic spin-glass insulator with two successive glassy freezing temperatures, i.e., transverse $(T_{TF}=9\mathrm{K})$ and longitudinal $(T_{LF}=55\mathrm{K})$. In this article, we present the results of measurements of complex dielectric behavior, electric polarization as a function of temperature $\left(T\right)$, in addition to characterization by magnetic susceptibility and heat capacity, primarily to explore magnetoelectric (ME) coupling and multiglass properties in uniaxial anisotropic spin-cluster-glass FTO. The existence of two magnetic transitions is reflected in the isothermal magnetodielectric (MD) behavior in the sense that the sign of MD is different in the $T$ regime $T<T_{TF}$ and $T>T_{TF}$. The data in addition provide evidence for the glassy dynamics of electric dipoles; interestingly, this occurs at much higher temperature (∼100–150 K) than $T_{LF}$, with high remnant polarization at 10 K $(\sim 4000\mu \mathrm{C}/{\mathrm{m}}^2)$ attributable to short-range magnetic correlations, thereby offering a route to attain ME coupling above 77 K.

Figure 1

Rietveld refinement of an x-ray diffraction pattern of ${\mathrm{Fe}}_2\mathrm{Ti}{\mathrm{O}}_5$ at room temperature.

Figure 2

For ${\mathrm{Fe}}_2\mathrm{Ti}{\mathrm{O}}_5$, temperature dependence of (a) dc magnetization measured in zfc and fc mode in 500 Oe. The lower inset shows $M_{\mathrm{zfc}\mathrm{ref}}$ and $M_{\mathrm{zfc}w}$ curves obtained with 4 h waiting at 40 K as described in the text; the upper inset shows ${\chi }^{-1}\mathrm{vs}T$ up to 310 K. (b) Real part of ac susceptibility measured with ν = 0.13 and 13 Hz; inset shows ac χ in an expanded scale near $T_{LF}$. (c) Heat capacity divided by temperature as a function of temperature; in the inset, the curve is shown in an expanded form in the $T$ range 100–200 K.

Figure 3

Panels (a) and (b) show temperature dependence of the real part $\left({\varepsilon }^{\prime }\right)$ of the dielectric constant and $\tan \delta$ for ${\mathrm{Fe}}_2\mathrm{Ti}{\mathrm{O}}_5$ at different frequencies. The arrows indicate the direction in which curves move with increasing frequency; inset in (b) illustrates the memory effect at 30 K at 50 kHz after waiting at 30 K for 15 h. Panel (c) illustrates the first derivative of ${\varepsilon }^{\prime }$ vs $T$ at two frequencies; inset shows power-law dependence of the peak in $d\left(\tan \delta \right)/dT$, as described in the text. Panel (d) shows isothermal magnetodielectric data $MD\left[=\left({{\varepsilon }^{\prime }}_H-{{\varepsilon }^{\prime }}_{H=0}\right)/\varepsilon {}_{H=0}^{\prime }\right]$ at different temperatures measured at 100 kHz; inset shows the coefficient of quadratic term $\left({\beta }_2\right)$ as a function of temperature. (For more details about fitting, see the text.)

Figure 4

(a) Temperature dependence of remnant polarization $\left(P\right)$ at 0 and 140 kOe (for details see text); pyroelectric current is also shown in the inset. (b) Derivative of dc $\chi$ measured at 500 Oe; inset shows $d^2\chi /d{T}^2\mathrm{vs}T$ behavior.