Room‐temperature multiferroicity in NiFe <sub>2</sub> O <sub>4</sub> and its magnetoelectric coupling intensified through defect engineering
Jae‐Hyeon Cho, Seongwoo Cho, Jun Han Lee, Haribabu Palneedi, Ju‐Hyeon Lee, Hwang-Pill Kim, Nyun Jong Lee, Siriporn Tigunta, Soodkhet Pojprapai, Sanghoon Kim, Jungho Ryu, Yoon Seok Oh, Seungbum Hong, Wook Jo
Abstract
Abstract The well‐known ferromagnetic oxide, NiFe 2 O 4 , was studied as a potential candidate for room‐temperature Type II magnetoelectrics. A spin canting as one of the essential requirements for Type II multiferroics was induced by breaking the stoichiometry, that is, intentionally subtracting Fe ions. We observed that Fe ions were first subtracted exclusively from the tetrahedral sites, leading to an increase in the magnetoelectric coupling owing to an increasing degree of spin canting. The enhancement in the magnetoelectric coupling culminated beyond the subtraction level of ~30 at.%, at which Fe ions started to be removed from the octahedral sites. Alongside, we observed that the subtraction of Fe ions gives rise to a ferroelectricity due to the formation of defect complexes that establish an internal bias field.