Strain-mediated Magnetic And Transport Properties Of Spinel Ferrite Films

Spinel ferrite,as a typical representative of transition metal oxides in the strong correlation system,has important applications in spintronic devices.Spinel ferrite exhibits large sensitivity to strain due to the coupled spin,charge,lattice and orbital degrees of freedom.As a consequence,mediating and optimizing the physical properties of spinel ferrite by strain will promote the application and development of spintronic devices.We fabricated the epitaxial Lu_xFe_3–xO₄?0?x?0.26?films on SrTiO₃ and MgO substrates by DC magnetron reactive sputtering,and investigated the static strain mediated structure,magnetic and transport properties of spinel ferrite films.The epitaxial Lu_xFe_3–xO₄ films are grown on SrTiO₃ and MgO substrates with in-plane compressive and tensile strains,respectively.The Lu_xFe_3–xO₄ films on SrTiO₃substrates exhibit larger saturation magnetization,smaller exchange bias and coercivity.Phase shift of anisotropic magnetoresistance is also observed in the Lu_xFe_3–xO₄ films on SrTiO₃ substrates.In addition,with the increasing Lu content,the out-of-plane lattice constant of the Lu_xFe_3–xO₄ films on SrTiO₃ substrates decreases while that on MgO substrates increases.The increase of Lu content enhances the spin canting,which further increases the exchange bias and coercivity,strengthens the four-fold symmetry of anisotropic magnetoresistance and the two-fold symmetry of planar Hall effect.Dynamic strain mediated magnetic property was further studied in spinel ferrite films with different densities of oxygen vacancies,grown on the?011?-Pb(Mg_1/3Nb_2/3)_0.7Ti_0.3O₃ single crystal substrates by DC magnetron reactive cosputtering.Owing to the volatile strain effect of substrate,the magnetization of the CoFe₂O₄ films decreases along[01?1]direction whereas it increases along[100]direction under the electric field,which attributes to the octahedron distortion in the spinel ferrite.Moreover,only two different magnetization states exist in the CoFe₂O₄film under high oxygen flow rate?10 sccm?while four different magnetization states exist in the CoFe₂O₄ film under low oxygen flow rate?4 sccm?.The additional two different magnetization states derive from the ferroelectric-field mediation effect.It changes the oxygen vacancy distributions and influences the superexchange interactions in the CoFe₂O₄ film.The magnetization of the sample is different after removing the positive and negative fields.The cooperation of strain and ferroelectric-field effects achieves mediation of four different magnetization states in the CoFe₂O₄ film.