Uniaxial magnetic anisotropy of transition metal oxides: role of local lattice deformation

Abstract

We study the effects of the local lattice structure around magnetic ions, on the uniaxial magnetic anisotropy (MA) in transition metal oxides, particularly ferrites, using the electron theory. We address M-type hexagonal ferrites, tetragonally distorted spinel ferrites, and an ilmenite (CoMnO3). The tight-binding scheme with spin–orbit interaction (LS coupling) is applied to calculate the electronic structure and MA energy of small clusters composed of a transition metal (TM) ion and surrounding oxygen ions. The results of uniaxial MA for M-type ferrites agree with those calculated using the first principles as well as those obtained experimentally, indicating the validity of the present scheme. The high numerical accuracy enables us to conclude that the p − d mixing between Fe3+ and O2− ions is crucial for the uniaxial MA of M-type ferrites and that a change in the local lattice structure around TM ions may cause a sign change in the local uniaxial MA of Fe2+ or Co2+ doped in M-type ferrites. The results of the uniaxial MA in tetragonally distorted spinel ferrites agree well with the experimental ones. These observations may indicate a feasible method to enhance the magnitude of the uniaxial MA in ferrites.

Magnetic anisotropy of Y-type ferrites: Role of the local lattice structure

“…[32]. Other parameter values for the 3d-and 2p-orbitals are the same as those used in the previous study [20][21][22]. The LS coupling is given as H SO = ξl • s, which is expressed as a 10 by 10 matrix by using eigen functions of orbital and spin angular momenta.…”

“…The magnitude of the LS coupling is defined as a coefficient multiplied to the matrix and is denoted as λ hereafter. The values of λ are 57 and 20 meV for Fe 3 + and M 2 + ions, respectively [22,33,34]. The contribution of the dipole-dipole interaction is neglected because it is much smaller than that of the LS coupling [36].…”

“…We take two lattice structures, Co 2 Y and Zn 2 Y [31]. The value of SOI λ = 57 meV, which is the same as that used in previous studies [20,22]. The local MA energies on the non-equivalent sites are given in table 4.…”

“…We recently conducted a theoretical study on MA for transition metal (TM) oxides, particularly for M-type and spinel ferrites, by calculating the electronic states of the TM ions surrounded by oxygen (O) ions [20][21][22]. In this study, we used a tight-binding (TB) Hamiltonian with LS coupling [23].…”

Origin of Perpendicular Magnetic Anisotropy in Co$_x$Fe$_{3-x}$O$_{4+δ}$ Thin Films Studied by X-ray Magnetic Circular and Linear Dichroisms

“…Historically, magnetic anisotropy in bulk CFO has been understood as an effect that the average of <111> easy axes direction produces cubic anisotropy in Co 2+ [28][29][30]. Recent theoretical and experimental investigations for CFO thin films suggest that the tensile strain into CFO layer produces the PMA [31][32][33][34][35][36][37][38]. Squareness of outof-plane hysteresis curves depends on the growth mode, such as molecular-beam epitaxy, pulsed-laser deposition (PLD), or sputter deposition.…”