Ferromagnetic And Ferroelectric Properties Of Codoped LiNbO₃ Films

Multiferroic materials have attracted more and more attention as a new type of multi-functional material with a wide application in the research field of electronics. However, the single-phase multiferroics with simultaneous ferroelectric and ferromagnetic ordering are rare due to the mutex between the ferroelectricity and ferromagnetism. So people attempt to obtain the multiferroics by doping. Li Nb O3 is a very excellent ferroelectric materials, and some researches have doped other element into the ferroelectric Li Nb O3 films to obtain the ferromagnetism. But it easily produced large leakage current and reduce its ferroelectric at the same time. At present, most studies obtain the ferromagnetism by doping the TM element into Li Nb O3 films, but it easily produced large leakage current and reduce its ferroelectric at the same time.In this paper, the Fe-Ca, Fe-Ba and Ba-Ca doped Li Nb O3 films were deposited on Si O2/Si(111) substrates by RF-magnetron sputtering technique. The structure and physical properties of these films have been investigated systemically by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), X-ray absorption fine structure(XAFS) and magnetic measurements(SQUID), and Ferroelectric properties were investigated by TF Analyner 2000 and impedance analyzer. Here are the results:(1) The local structural, ferroelectric and ferromagnetic of Fe, Ca doped LiNbO3 films have been studied. The Fe ions substituted Li and Nb with Vo in the form of Fe2+ and Fe3+, and Ca ions substituted Li with VLi in the form of Ca2+. And there’s no secondary phase such as Fe and Ca or their oxide existed in the doped Li Nb O3 films. SQUID results show that all the doped Li Nb O3 films have room temperature ferromagnetism, and the ferromagnetism of Fe-Ca codoped Li Nb O3 film is larger than the Ca doped Li Nb O3 film. The dielectric constant of the Fe-Ca codoped Li Nb O3 film is larger than the Fe doped Li Nb O3 film. The Ferroelectric Curie temperature of all the doped Li Nb O3 films is lower than the pure Li Nb O3 thin film.(2) The local structural, ferroelectric and ferromagnetic of Fe, Ba doped LiNbO3 films have been investigated. The Fe ions substituted Li and Nb with Vo in the form of Fe2+ and Fe3+, and Ba ions substituted Nb with Vo in the form of Ba2+. And there’s no secondary phase such as Fe and Ba or their oxide existed in the doped Li Nb O3 films. All the doped Li Nb O3 films show typical room temperature ferromagnetism, and the ferromagnetismof Fe-Ba codoped Li Nb O3 films is larger than the Fe,Ba single doped Li Nb O3 films, and its dielectric loss also larger than the single doped one.(3) The structural composition, magnetic and ferroelectricity of the Ba, Ca doped Li Nb O3 films have been investigated systematically. The Ba ions substituted Nb with Vo in the form of Ba2+, and Ca ions substituted Li with VLi in the form of Ca2+. And there’s no secondary phase such as Ba and Ca or their oxide existed in the doped Li Nb O3 films. All the dopedLi Nb O3 films show typical room temperature ferromagnetism, and the ferromagnetism of Ba-Ca codoped Li Nb O3 films is larger than the single doped Li Nb O3 films, But its dielectric constant also larger than the single doped one. The Ferroelectric Curie temperatureof all the doped Li Nb O3 films are lower than the undoped Li Nb O3 film.