Abstract: In the past years, magnetism-driven ferroelectricity and gigantic magnetoelectric effects have been reported for a number of frustrated magnets with spiral magnetic orders. Such materials are of high current interest due to their potential for spintronics and low-power magnetoelectric devices. However, their low magnetic order temperatures (typically <100K) greatly restrict their fields of application.

In this talk, I will show that chemical disorder is a powerful tool that can be used to stabilize magnetic spiral phases at higher temperatures. As example of this novel mechanism, I will present our recent investigations on YBaCuFeO₅, where a controlled manipulation of the Cu/Fe chemical disorder was successfully used to increase the spiral order temperature T_spiral from 154 to 310K. Combination of this novel mechanism with a targeted lattice control of some magnetic interactions allowed us to obtain T_spiral values close to 400 K, comfortably far from room temperature and almost 100 K higher than using chemical disorder alone. Another interesting property of YBaCuFeO₅ is that the spiral modulation is accompanied by the appearance of weak ferromagnetism. Since ferromagnets can be easily manipulated with magnetic fields, this observation opens new perspectives for the control of the spiral orientation, directly linked to the polarization direction, as well as for a possible future use of this material in technological applications.