Extraordinarily large perpendicular magnetic anisotropy in epitaxially strained cobalt-ferrite CoxFe3−xO4(001) (x = 0.75, 1.0) thin films

Abstract

Perpendicular magnetic anisotropy (PMA) of cobalt-ferrite CoxFe3-xO4 (x = 0.75 and 1.0) epitaxial thin films grown on MgO (001) by a reactive magnetron sputtering technique was investigated. The saturation magnetization was found to be 430 emu/cm3 for x = 0.75, which is comparable to that of bulk CoFe2O4 (425 emu/cm3). Torque measurements afforded PMA constants of Kueff=9.0 Merg/cm3 (Ku=10.0 Merg/cm3) and Kueff=9.7 Merg/cm3 for x = 0.75 and 1.0, respectively. The value of Kueff extrapolated using Miyajima's plot was as high as 14.7 Merg/cm3 for x = 1.0. The in-plane four-fold magnetic anisotropy was evaluated to be 1.6 Merg/cm3 for x = 0.75. X-ray diffraction measurement revealed our films to be pseudomorphically strained on MgO (001) with a Poisson ratio of 0.4, leading to a considerable in-plane tensile strain by which the extraordinarily large PMA could be accounted for.

Magnetic Properties of Spinel Ferrite Thin Films Grown by Reactive Sputtering

“…Recently, we found that CFO lms grown on MgO(001) substrates by reactive sputtering exhibit large saturation magnetization comparable to the bulk and extremely high uniaxial magnetic anisotropy of 13 Merg/cm 3 along the normal to the lm Co 0.75 Fe 2.25 O 4 (001) 6) . The composition ratio of Fe and Co is also a crucial parameter 18) .…”

“…Recently, we have found that high quality epitaxial lms of these spinel ferrites can be grown by reactive magnetron sputtering techniques and that epitaxial distortion causes the ferrite lm to exhibit high magnetic anisotropy. 6) In this paper, we present an overview of the developed lm growth technique based on a reactive sputtering method and the magnetic and structural properties of the as-grown epitaxial thin lms magnetite, maghemite, and cobalt-ferrite. In the following section, the experimental procedures for growing spinel ferrite lms are described.…”

“…Since some of the spinel ferrites exhibit relatively large magnetization and a much higher Curie temperature as compared to room temperature 1) , they have been utilized in various magnetic devices as well as recording technology. For example, magnetite (Fe 3 O 4 ) is believed to be half-metallic 2) ; cobalt and nickel ferrites are promising insulators used as tunneling barriers in a spin lter device [3][4][5] ; epitaxially distorted cobalt ferrite thin lms possess high magnetic anisotropy and are potentially useful in magnetic recording media unaccompanied by platinum group elements or rare earth elements [6][7][8] . Magnetite is composed of only two elements, iron and oxygen, and is a prototype spinel ferrite.…”

Spin Hall magnetoresistance at the interface between platinum and cobalt ferrite thin films with large magnetic anisotropy

“…Among many ferromagnetic oxides, cobalt ferrite (CFO) shows a significantly large magnetoelastic effect. 17,18 The easy axis can be varied between the out-of-plane and in-plane directions by changing the lattice distortion if CFO is in a film form. A previous report revealed that epitaxial CFO on MgO (001) shows a large perpendicular magnetic anisotropy of K u of over 1 MJ/m 3 under a tensile strain.…”

“…The effective uniaxial magnetic anisotropy constant K u evaluated by magneto-torque measurements at RT, was K u ∼ 1 MJ/m 3 and -5.2 MJ/m 3 for CFO/MgO and CFO/MAO, respectively. 17,24 Those values of K u were extracted from the high-field torque data using Miyajima's analysis. 25 We note that the easy axis is defined as perpendicular to the film; therefore, a positive value of K u means a perpendicular magnetization film.…”