title: Polar-Graded Multiferroic SrMnO3 Thin Films.
abstract: Engineering defects and strains in oxides provides a promising route for the quest of thin film materials with coexisting ferroic orders, multiferroics, with efficient magnetoelectric coupling at room temperature. Precise control of the strain gradient would enable custom tailoring of the multiferroic properties but presently remains challenging. Here we explore the existence of a polar-graded state in epitaxially strained antiferromagnetic SrMnO3 thin films, whose polar nature was predicted theoretically and recently demonstrated experimentally. By means of aberration-corrected scanning transmission electron microscopy we map the polar rotation of the ferroelectric polarization with atomic resolution, both far from and near the domain walls, and find flexoelectricity resulting from vertical strain gradients. The origin of this particular strain state is a gradual distribution of oxygen vacancies across the film thickness, according to electron energy loss spectroscopy. Herein we present a chemistry-mediated route to induce polar rotations in oxygen-deficient multiferroic films, resulting in flexoelectric polar rotations and with potentially enhanced piezoelectricity.
authors.affiliation: Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza , 50018 Zaragoza, Spain.
authors.forename: Roger
authors.initials: R
authors.lastname: Guzmán
authors.affiliation: Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza , 50018 Zaragoza, Spain.|Departamento de Física de la Materia Condensada, Universidad de Zaragoza , 50009 Zaragoza, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Maurel
authors.affiliation: Departamento de Física de la Materia Condensada, Universidad de Zaragoza , 50009 Zaragoza, Spain.|Instituto de Ciencia de Materiales de Aragón (ICMA), Universidad de Zaragoza-CSIC , 50009 Zaragoza, Spain.
authors.forename: Eric
authors.initials: E
authors.lastname: Langenberg
authors.affiliation: Materials Science and Technology Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Lupini
authors.affiliation: Departamento de Física de la Materia Condensada, Universidad de Zaragoza , 50009 Zaragoza, Spain.|Instituto de Ciencia de Materiales de Aragón (ICMA), Universidad de Zaragoza-CSIC , 50009 Zaragoza, Spain.
authors.forename: Pedro A
authors.initials: PA
authors.lastname: Algarabel
authors.affiliation: Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza , 50018 Zaragoza, Spain.|Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza , 50018 Zaragoza, Spain.|Departamento de Ciencia y Tecnología de Materiales y Fluidos, Universidad de Zaragoza , 50018 Zaragoza, Spain.
authors.forename: José A
authors.initials: JA
authors.lastname: Pardo
authors.affiliation: Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza , 50018 Zaragoza, Spain.|Departamento de Física de la Materia Condensada, Universidad de Zaragoza , 50009 Zaragoza, Spain.|Fundación ARAID , 50004 Zaragoza, Spain.
authors.forename: César
authors.initials: C
authors.lastname: Magén
keywords: Multiferroics; aberration-corrected STEM; domain walls; ferroelectricity; flexoelectricity