Magnetism in multiferroic Pb${}_5$Cr${}_3$F${}_{19}$

We report on the first observation of a magnetic transition in multiferroic Pb${}_5$Cr${}_3$F${}_{19}$. The system undergoes a ferroelectric transition at $T_{\mathrm{C}}$ $=$ 545 K and probably an antiferromagnetic transition around $T_{\mathrm{N}}$ $=$ 11 K. Between 50 K and $T_{\mathrm{N}}$, the system is not paramagnetic but shows the presence of correlated spin clusters, indicating a superparamagnetic or spin glass state. The observable changes of the magnetic properties ongoing through ferroelectric phase transition show a magnetoelectric coupling that may be important for new devices.

Figure 1

Crystal structure of Pb${}_5$Cr${}_3$F${}_{19}$ (Ref. 5).

Figure 2

(a) High-temperature X-band EPR spectra of Pb${}_5$Cr${}_3$F${}_{19}$ and (b) low-temperature X-band EPR spectra. The horizontal “zero amplitude line” in (b) helps us see the EPR line asymmetry and the appearance of a new broad line below 20 K.

Figure 3

Temperature dependence of the (a) EPR line width and (b) $g$-factor in Pb${}_5$Cr${}_3$F${}_{19}$ close to the ferroelectric transition.

Figure 4

Temperature dependence of the (a) EPR intensity, (b) line width, and (c) $g$-factor of the central line below room temperature.

Figure 5

Inverse EPR susceptibility versus temperature for the central line.

Figure 6

Cr${}^{3+}$ EPR line broadening as a function of temperature for the central line. The solid line is the fit of the experimental data to Eq. (4).

Figure 7

Excess line width as a function of $T$/$T_0$ $-$ 1.

Figure 8

Temperature dependence of the (a) EPR line intensity, (b) line width, and (c) $g$-factor for the broad line in Pb${}_5$Cr${}_3$F${}_{19}$ at low temperatures.

Figure 9

Temperature dependence of $\chi$·$T$ as obtained from ZFC SQUID magnetic susceptibility data of Pb${}_5$Cr${}_3$F${}_{19}$ at $H$ $=$ 100 Oe. The inset shows $\Delta \chi$ versus ($T_{\mathrm{c}}$ $-$ $T$).

Figure 10

Magnetization as a function of the magnetic field at $T$ $=$ 2 and 5 K. The inset shows $M$ versus $H$ at $T$ $=$ 500 and 580 K.