Magnetic structure and ferroelectric activity in orthorhombic YMnO3: Relative roles of magnetic symmetry breaking and atomic displacements / Solovyev I. V.,Valentyuk M. V.,Mazurenko V. V. // PHYSICAL REVIEW B. - 2012. - V. 86, l. 14.

ISSN/EISSN:

2469-9950 / 2469-9969

Type:

Article

Abstract:

We discuss the relative roles played by the magnetic inversion symmetry breaking and the ferroelectric (FE) atomic displacements in the multiferroic state of YMnO3. For these purposes we derive a realistic low-energy model, using results of first-principles electronic structure calculations and experimental parameters of the crystal structure below and above the FE transition. Then, we solve this model in the mean-field Hartree-Fock approximation. We argue that the multiferroic state in YMnO3 has a magnetic origin, and the centrosymmetric Pbnm structure is formally sufficient for explaining the main details of the noncentrosymmetric magnetic ground state. The relativistic spin-orbit interaction lifts the degeneracy, caused by the frustration of isotropic exchange interactions in the ab plane, and stabilizes a twofold periodic noncollinear magnetic state, which is similar to the E state apart from the spin canting. The noncentrosymmetric atomic displacements in the P2(1)nm phase reduce the spin canting, but do not change the symmetry of the magnetic state. The effect of the P2(1)nm distortion on the FE polarization Delta P-a, parallel to the orthorhombic a axis, is twofold: (i) It gives rise to ionic contributions, associated with the oxygen and yttrium sites; (ii) it affects the electronic polarization, mainly through the change of the spin canting. The relatively small value of Delta P-a, observed in the experiment, is caused by a partial cancellation of the electronic and ionic contributions, as well as different contributions in the ionic part, which takes place for the experimental P2(1)nm structure. The twofold periodic magnetic state competes with the fourfold periodic one and, even in the displaced P2(1)nm phase, these two states continue to coexist in a narrow energy range. Finally, we theoretically optimize the crystal structure. For these purposes we employ the LSDA+U approach and assume the collinear E-type antiferromagnetic alignment. Then, we use the obtained structural information again as the input for the construction and solution of the low-energy model. We have found that the agreement with the experimental data in this case is less satisfactory and |Delta P-a| is largely overestimated. Although the magnetic structure can be formally tuned by varying the Coulomb repulsion U as a parameter, apparently LSDA+U fails to reproduce some fine details of the experimental structure, and the cancellation of different contributions in Delta P-a does not occur.

Author keywords:

POLARIZATION; MULTIFERROICS

DOI:

10.1103/PhysRevB.86.144406

Web of Science ID:

ISI:000309651200002

Соавторы в МНС:

Другие поля

Поле	Значение
Month	OCT 10
Publisher	AMER PHYSICAL SOC
Address	ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA
Language	English
Article-Number	144406
EISSN	2469-9969
Keywords-Plus	POLARIZATION; MULTIFERROICS
Research-Areas	Physics
Web-of-Science-Categories	Physics, Condensed Matter
Author-Email	solovyev.igor@nims.go.jp
ResearcherID-Numbers	Mazurenko, Vladimir/P-9241-2017 Solovyev, Igor/B-1320-2010
ORCID-Numbers	Solovyev, Igor/0000-0002-2010-9877
Funding-Acknowledgement	Ministry of Education and Science of Russia {[}N 14.A18.21.0889]
Funding-Text	The work is partly supported by the grant of the Ministry of Education and Science of Russia N 14.A18.21.0889.
Number-of-Cited-References	24
Usage-Count-Last-180-days	3
Usage-Count-Since-2013	72
Journal-ISO	Phys. Rev. B
Doc-Delivery-Number	018HP