Magnetoelectric effect in doped magnetic ferroelectrics

Abstract

We propose a model of magneto-electric effect in doped magnetic ferroelectrics. This magnetoelectric effect does not involve the spin-orbit coupling and is based purely on the Coulomb interaction. We calculate magnetic phase diagram of doped magnetic ferroelectrics. We show that magneto-electric coupling is pronounced only for ferroelectrics with low dielectric constant. We find that magneto-electric coupling leads to modification of magnetization temperature dependence in the vicinity of ferroelectric phase transition. A peak of magnetization appears. We find that magnetization of doped magnetic ferroelectrics strongly depends on applied electric field.

Competition of the Coulomb and hopping-based exchange interactions in granular magnets

“…Recently the exchange interaction between magnetic grains was considered using the HamiltonianĤ 0 + H dC [27]. However, later it was shown [31] that the indirect Coulomb interaction may also lead to magnetic coupling between the FM contacts.…”

“…However, it is known that the manybody Coulomb interaction also leads to the magnetic exchange interaction [29 and 30]. Recently, the Coulomb based exchange interaction was considered in MTJ [31]. It was shown that this contribution to the magnetic interaction between magnetic leads separated by the insulating layer is comparable and even larger than the hopping based exchange coupling.…”

“…Numerous papers were devoted to magnetic anisotropy and magneto-dipole interaction [15][16][17][18][19][20][21][22]. Much less is known about the exchange interaction between magnetic grains [23][24][25][26][27]. The influence of the intergrain exchange coupling on the magnetic state of the whole granular magnet are currently understood, however the microscopic picture of the intergrain exchange interaction is still missing.…”

“…Usually, the coupling between grains was estimated using this model by taking into account the grains surface area. Recently, it was shown that the intergrain coupling differs from the exchange coupling in MTJ [27]. In granular system the exchange coupling depends not only on the distance between the grains and on the insulating matrix barrier, but also on the dielectric properties of the matrix.…”

“…[31] it was shown that the Coulomb based coupling strongly depends on the insulator dielectric constant. For granular system both the hopping and the Coulomb based exchange depends on the matrix dielectric susceptibility.…”