Spin reorientation in single-crystal CoFe₂O₄ thin films

Abstract

Reorientation of magnetic anisotropy has been observed in single-crystal CoFe 2 O 4 thin films deposited on (100) MgO substrate by pulsed laser deposition (PLD). The as-grown film exhibits a perpendicular anisotropy whereas after annealing the magnetization easy axis switches to be parallel to the film plane. The origin of such spin reorientation is explained in terms of competition between stress and magnetocrystalline anisotropies. The as-prepared film is under tensile stress, which induces a huge perpendicular uniaxial anisotropy dominating the in-plane magnetocrystalline component. Annealing releases the stress by relaxing the film lattice. Consequently, the perpendicular stress anisotropy is considerably reduced and magnetocrystalline anisotropy prevails, leading to an in-plane alignment of the easy axis.

Epitaxial strain effects in the spinel ferritesCoFe2O4andNiFe2O

“…For sufficient amount of strain the easy axis of magnetization will therefore always be oriented either in-plane or out-of-plane, consistent with various experimental observations in thin CoFe 2 O 4 films under tensile strain. 13,14,48 According to the phenomenological magnetoelastic theory for a cubic crystal discussed in Sec. II B, in particular Eqs.…”

Effects of substrate temperature and oxygen pressure on the magnetic properties and structures of CoFe2O4 thin films prepared by pulsed-laser deposition

“…The texture of the epitaxial film is strongly affected by the crystal structure of the substrate. Therefore, the CoFe 2 O 4 films with (0 0 1) orientation were grown on MgO (0 0 1) because the former lattice is about twice the later lattice [8,11,12]. Silicon lattice parameter is far from that of CoFe 2 O 4 and thus it is very hard to deposit CoFe 2 O 4 epitaxial film on it.…”

“…So, some research groups focused on improving the coercivity [9,10] and studying the magnetic anisotropy [6] of CoFe 2 O 4 . The epitaxial CoFe 2 O 4 films were mainly grown on oxide single crystal substrates, such as MgO [8,11,12] and SrTiO 3 [13] for their nearly half unit cell in comparison with the spinel ferrites. Silicon is one of the cheapest substrates.…”

Epitaxial strain effects in the spinel ferrites CoFe2O4 and NiFe2O4 from first principles

“…This gives further confirmation that the reorientation of the easy axis observed experimentally in thin films of CoFe 2 O 4 under different conditions is indeed predominantly strain-driven. 13,14,48 In summary, our results indicate that a quantitative description of both structural and magnetoelastic properties in spinel ferrites is possible within the DFT+U approach, which opens the way for future computational studies of these materials. Such calculations can then provide important information regarding the effect of cation inversion and off-stoichiometry, which can be used to optimize magnetostriction constants and anisotropy in spinel ferrites.…”