Speaker
Description
ErMnO$_3$ is the improper multiferroic compound with ferroelectric ordering temperature of $T_c$ = 835 K, but with the magnetism presented only below Neel temperature of $T_N$ = 81 K [1]. This temperature is too low for the application purposes. On the other hand, ErFeO$_3$ system does not exhibit the ferroelectric ordering, but it orders magnetically into antiferromagnetic structure below $T_N$ = 643 K [2]. In order to have a multiferroic material with high application potential, one has to ensure that both, ferroelectric and magnetic orderings occur at temperature higher than room temperature. Extrapolating from parent ErMnO$_3$ and ErFeO$_3$ compound we have expected that such a material can be found in the ErMn$_{1-x}$Fe$_{x}$O$_3$ substitutional system. For these reasons we have prepared the Fe-doped ErMnO$_3$ materials and examined their magnetic properties.
Nanopowders of ErMn$_{1-x}$Fe$_{x}$O$_3$ ($0 \leq x \leq 1$) were prepared by nitrate glycine method. The compounds crystallize in hexagonal structure for $0 \leq x \leq 0.2$ and in orthorhombic structure for $0.5 \leq x \leq 1$. The co-existence of both, hexagonal and orthorhombic phase was observed in the concentration range $0.2 < x < 0.5$. Since the multiferroicity was observed in the hexagonal phase, the magnetism was investigated for $0 \leq x \leq 0.2$ compounds. It was found that all compounds order magnetically at low temperatures, exhibiting hysteresis loops [$M(B)$] at 2 K with very low coercivity field of 0.06 T; 0.04 T and 0.035 T and very low remnant magnetization of 0.18 $\mu_{B}/\mathrm{f.u.}$; 0.1 $\mu_{B}/\mathrm{f.u.}$ and 0.08 $\mu_{B}/\mathrm{f.u.}$ for $x$ = 0; 0.1 and 0.2 composition. The hysteresis loops do not saturate at magnetic field of $\mu_0 H$ = 5 T. No visible anomalies can be observed on $dTM(T)/dT$ curves. Anomalies in $d^2TM(T)/dT^2$ which we associate with magnetic phase transition, are located at 76.9 K, 79.7 K and 82.4 K. All samples are paramagnetic at 150 K as proven from $M(B)$ loops at this temperature and the Curie-Weiss fit of the high temperature $M(T)$ curves indicate that the anomaly in $d^2TM(T)/dT^2$ is connected with paramagnetic to weak ferromagnetic / canted antiferromagnetic phase transition.
Concluding, Neel temperature increases with iron doping, but it does not reach the room temperature within the concentration range of stable hexagonal crystal structure. The magnetic ordering phase transition is of higher order. Additional consequences and effects of the Mn-Fe doping in this system will be discussed within the conference contribution.
Acknowledgements
This research has been supported by VEGA Project No. 2/0011/22.
References
[1] F. Yen et al., “Magnetic phase diagrams of multiferroic hexagonal RMnO3 (R = Er, Yb, Tm, and Ho),” Journal of Materials Research, vol. 22, no. 8. Springer Science and Business Media LLC, pp. 2163–2173, Aug. 2007. doi: 10.1557/jmr.2007.0271.
[2] D. Treves, “Studies on Orthoferrites at the Weizmann Institute of Science,” Journal of Applied Physics, vol. 36, no. 3. AIP Publishing, pp. 1033–1039, Mar. 01, 1965. doi: 10.1063/1.1714088.
