Magnetoelectric Coupling Triggered by Noncollinear Magnetic Structure in M‐Type Hexaferrite

Abstract

Direct magnetoelectric (ME) coupling between magnetic and ferroelectric orders, which can be realized in spiral magnets, is vital in technological applications of multifunctional materials. Multisusceptible BaFe 12 O 19 is noteworthy for its excellent magnetic, dielectric properties and thus the application in high-density information storage, while its collinear spin structure limits the emergence of ferroelectrics and ME coupling. In this work, nonzero Dzyaloshinskii-Moriya (DM) interaction is created by partial substitution of the spin-down Fe 3+ sites to induce conical spin structure in BaFe 12 O 19 . Larger In 3+ ions are introduced and prefer to occupy the spin-down 4f 1 and 4f 2 lattice sites. The evolution of magnetization versus temperature adduces evidence of conical magnetic structure. As a result, direct ME and magnetodielectric coupling are obtained in In-doped BaFe 12 O 19ceramics. An interlayer DM interaction model is built to discuss the intrinsic relationship among crystal structure, noncollinear magnetic structure, and ionic substitution. Moreover, BaZn 0.9 Zr 0.9 Fe 10.2 O 19 ceramics are also prepared, and exhibit noncollinear magnetic structure and direct ME coupling since Zn 2+ and Zr 4+ also possess larger radii than Fe 3+ and prefer to enter the spin-down sites. The present result provides a feasible avenue to develop multiferroic and magnetoelectric coupling in ubiquitous M-type hexaferrite.

Magnetoelectric coupling induced by Jahn–Teller Cu2+ in SrFe12O19 ceramics

“…7(g–l), the relative P spin as H sweeps from −20 kOe to +20 kOe is smaller than that when H sweeps from +20 kOe to −20 kOe. This is different from the typical ME coupling behaviour of type II multiferroics, where the hysteresis loop 24,36 or butterfly 7,10 P spin –H curves are usually observed. In order to further understand such decay behaviour, relative P spin is measured by periodic H under H⊥E conditions at 10 K. Fig.…”

“…That is to say, the uniaxial magnetocrystalline anisotropy of SrFe 12 O 19 is weakened effectively by the introduction of Cu 2+ and Ti 4+ ions, which is necessary for the formation of a conical magnetic structure in M-type hexaferrite. [9][10][11] The magnetic hysteresis loop at 10 K (Fig. 3 Fig.…”

“…9,22 The abnormal temperature, where M FC stops to increase rapidly with decreasing temperature, represents that the collinear spin order starts to transform to conical spin order and is defined as T cone . 9,10,22 The cone angle y usually increases with decreasing temperature, 23 and consequently more spin projections on the cone bottom balance themselves out, bringing about decreased M FC with decreasing temperature. It should be mentioned that, as the temperature decreases, the M FC of polycrystalline Sr(CuTi) x Fe 12À2x O 19 ceramics, which differs from the obviously decreased value in the Sc 3+ doped BaFe 12 O 19 single crystal, 22 only stops increasing or even slightly increases below T cone probably due to the random distribution of crystal orientations.…”

“…No matter what mechanism works, the hard magnetic properties of SrFe 12 O 19 /BaFe 12 O 19 are all weakened. Therefore, much smaller coercive field ( H c ) is obtained in the doped samples with a spiral magnetic structure, 9–11 implying the weakening or destroying of the uniaxial magnetocrystalline anisotropy. Fe 3+ ions contribute positive single-ion anisotropy and are responsible for the uniaxial anisotropy of SrFe 12 O 19 .…”

“…Recently, a spiral magnetic structure was induced by Sc 3+ , Co 2+ -Ti 4+ and In 3+ doping in SrFe 12 O 19 and/or BaFe 12 O 19 , and the coexistence of multiferroics and ME coupling was thus realized. [9][10][11] The ME effect is usually discussed based on an inverse Dzyaloshinskii-Moriya (DM) model [P i, j p e i, j  (S i  S j )] and/or a d-p hybridization model [P i, j p (a i, j ÁS i ) 2 a i, j ], 12,13 where S i and S j represent the spins at neighbouring sites i and j, respectively, e i, j represents the unit vector between sites i and j, and a i, j refers to the unit vector from magnetic ionic site i to its neighbouring ligand site j. No matter what mechanism works, the hard magnetic properties of SrFe 12 O 19 /BaFe 12 O 19 are all weakened.…”