AUTHOR=Wu Linjie , Zhang Yongjia , Nie Zhongquan , Cao Ensi 

TITLE=Intrinsic Complex Vacancy-Induced d0 Magnetism in Ca2Nb2O7 PLD Film

JOURNAL=Frontiers in Materials

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2021.736011

DOI=10.3389/fmats.2021.736011

ISSN=2296-8016

ABSTRACT=<p>Introducing magnetism into the ferroelectric Ca<sub>2</sub>Nb<sub>2</sub>O<sub>7</sub> with high Curie temperature can make it a potential multiferroic material at room temperature. Stoichiometric Ca<sub>2</sub>Nb<sub>2</sub>O<sub>7</sub>, nonstoichiometric Ca<sub>1.9</sub>Nb<sub>2</sub>O<sub>7-δ</sub> and Ca<sub>2</sub>Nb<sub>1.9</sub>O<sub>7-δ</sub> single phase films were deposited on STO (110) substrate by pulsed laser deposition under appropriate conditions. The films were characterized by XRD, FE-SEM, Element mapping and XPS. Both stoichiometric Ca<sub>2</sub>Nb<sub>2</sub>O<sub>7</sub> and Ca<sub>1.9</sub>Nb<sub>2</sub>O<sub>7-δ</sub> films were diamagnetic in the magnetic measurement and <italic>ab initio</italic> calculations, while the Ca<sub>2</sub>Nb<sub>1.9</sub>O<sub>7-δ</sub> film with the complex vacancy of V<sub>Nb+O</sub> exhibited ferromagnetic behavior at room temperature, with the saturated magnetization of 3.6 emu/cm<sup>3</sup>. Calculations on the Ca<sub>2</sub>Nb<sub>2</sub>O<sub>7</sub> (010) surface indicate that the V<sub>Nb+O</sub> can induce spin polarization on the residual O atoms around the Nb vacancies, and the system was most stable when the Nb and O vacancies were the 4<sup>th</sup> nearest-neighbored, with FM coupling energetically more stable than the AFM coupling. Our work verified experimentally and theoretically the feasibility of introducing ferromagnetism into Ca<sub>2</sub>Nb<sub>2</sub>O<sub>7</sub> film by the intrinsic complex vacancy of V<sub>Nb+O</sub>.</p>