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, EuTiO(3), was predicted to exhibit strong ferromagnetism (spontaneous magnetization, approximately 7 Bohr magnetons per Eu) and strong ferroelectricity (spontaneous polarization, approximately 10 microC 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.
Lee
June Hyuk
JH
Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853-1501, USA.
Fang
Lei
L
Vlahos
Eftihia
E
Ke
Xianglin
X
Jung
Young Woo
YW
Kourkoutis
Lena Fitting
LF
Kim
Jong-Woo
JW
Ryan
Philip J
PJ
Heeg
Tassilo
T
Roeckerath
Martin
M
Goian
Veronica
V
Bernhagen
Margitta
M
Uecker
Reinhard
R
Hammel
P Chris
PC
Rabe
Karin M
KM
Kamba
Stanislav
S
Schubert
Jürgen
J
Freeland
John W
JW
Muller
David A
DA
Fennie
Craig J
CJ
Schiffer
Peter
P
Gopalan
Venkatraman
V
Johnston-Halperin
Ezekiel
E
Schlom
Darrell G
DG
D025802:Electric Capacitance; D004560:Electricity; D005063:Europium / Q000737:chemistry*; D008280:Magnetics; D017348:Microscopy, Electron, Scanning Transmission; D010087:Oxides / Q000737:chemistry*; D013696:Temperature; D014025:Titanium / Q000737:chemistry*; D014961:X-Ray Diffraction
D010087:Oxides; C552630:europium titanium trioxide; D005063:Europium; D014025:Titanium