S. Kamba

A strong ferroelectric ferromagnet created by means of spin–lattice coupling

Ferroelectric ferromagnets are exceedingly rare, fundamentally interesting multiferroic materials that could give rise to new technologies in which the low power and high speed of field-effect electronics are combined with the permanence and routability of voltage-controlled ferromagnetism. Furthermore, the properties of the few compounds that simultaneously exhibit these phenomena are insignificant in comparison with those of useful ferroelectrics or ferromagnets: their spontaneous polarizations or magnetizations are smaller by a factor of 1,000 or more. The same holds for magnetic- or electric-field-induced multiferroics. Owing to the weak properties of single-phase multiferroics, composite and multilayer approaches involving strain-coupled piezoelectric and magnetostrictive components are the closest to application today. Recently, however, a new route to ferroelectric ferromagnets was proposed by which magnetically ordered insulators that are neither ferroelectric nor ferromagnetic are transformed into ferroelectric ferromagnets using a single control parameter, strain. The system targeted, EuTiO3, was predicted to exhibit strong ferromagnetism (spontaneous magnetization, ∼7 Bohr magnetons per Eu) and strong ferroelectricity (spontaneous polarization, ∼10 µC cm−2) simultaneously under large biaxial compressive strain. These values are orders of magnitude higher than those of any known ferroelectric ferromagnet and rival the best materials that are solely ferroelectric or ferromagnetic. Hindered by the absence of an appropriate substrate to provide the desired compression we turned to tensile strain. Here we show both experimentally and theoretically the emergence of a multiferroic state under biaxial tension with the unexpected benefit that even lower strains are required, thereby allowing thicker high-quality crystalline films. This realization of a strong ferromagnetic ferroelectric points the way to high-temperature manifestations of this spin–lattice coupling mechanism. Our work demonstrates that a single experimental parameter, strain, simultaneously controls multiple order parameters and is a viable alternative tuning parameter to composition for creating multiferroics.

Dielectric dispersion of the relaxor PLZT ceramics in the frequency range 20 Hz-100 THz

\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}

Infrared, Raman and high-frequency dielectric spectroscopy and the phase transitions in Na1/2Bi1/2TiO3

ceramics were investigated by means of infrared reflectivity and time domain terahertz transmission spectroscopy at temperatures

Dielectric spectroscopy of Ba(B1/2’B1/2‘)O3 complex perovskite ceramics: Correlations between ionic parameters and microwave dielectric properties. I. Infrared reflectivity study (1012–1014 Hz)

20\char21{}950\phantom{\rule{0.3em}{0ex}}\mathrm{K}

Structure of the dielectric spectrum of relaxor ferroelectrics

, and the magnetodielectric effect was studied at

Exploiting dimensionality and defect mitigation to create tunable microwave dielectrics

10\char21{}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}

Infrared dielectric response of relaxor ferroelectrics

with the magnetic field up to

High frequency dielectric properties of A5B4O15 microwave ceramics

9\phantom{\rule{0.3em}{0ex}}\mathrm{T}

Dielectric spectroscopy of Ba(B1/2’B1/2‘)O3 complex perovskite ceramics: Correlations between ionic parameters and microwave dielectric properties. II. Studies below the phonon eigenfrequencies (102–1012 Hz)

. Below