Spintronics with multiferroics

Abstract

This is a copy of the slides presented at the meeting but not formally written up for the volume. Multiferroics belong to a class of compounds which show simultaneous electric and magnetic orders. Consideration has been focused on this family of materials due to their potential for applications in electronics resulting from both the ferroelectric and magnetic orders and additional functionalities resulting from the coupling between these two orders. We will present experiments performed on multiferroic based heterostructures in order to check the potential of such multifunctional materials in the field of spintronics. Two kind of materials have been studied. The ferromagnetic-ferroelectric LaxBi1-xMnO3 (LBMO) (x ≤ 0.1) and the antiferromagnetic-ferroelectric BiFeO3 (BFO). The ferromagnetic and ferroelectric of LBMO offers the unique opportunity to encode information independently in electric polarization and magnetization to obtain four different logic states. To achieve this objective, ferromagnetic-ferroelectric (LBMO) (x ≤0.1) thin layers have been used as tunnel barriers in magnetic tunnel junction. In such device, the ferromagnetic and insulating character allows to filter the spin by an active barrier presenting a barrier height different for spin up and spin down tunneling electrons. To demonstrate spin filtering through LBMO barriers, we have analyzed the spin polarization of the current tunnelling from a nonmagnetic electrode (Au) with a half-metallic ferromagnetic oxide counter-electrode (La2/3Sr1/3MnO3 (LSMO)) through such ultrathin LBMO barrier (1 - 3.5 nm). A 100% change of the tunnel resistances is obtained at 3K depending on whether the magnetizations of LBMO(x = 0) and LSMO are parallel or opposite [1]. In addition, the ferroelectric character of the compound is exploited to give rise to two different resistance states related to the direction of the polarization. The resulting electroresistance phenomena amount to 20% at low temperature [3]. On the other hand, we have taken advantage of the antiferromagnetic character of BFO thin films [3], as evidenced by X-ray linear magnetic dichroism experiments, to induce a sizeable (~60 Oe) exchange bias on ferromagnetic films of NiFe and CoFeB, at room temperature. In parallel we have check the possibility to obtain large tunnel magnetoresistance through such antiferromagnetic barrier in LSMO/BFO/Co heterostructures. Perspectives of these findings for multiferroics-based spintronics devices will be discussed. [1] M. Gajek, M. Bibes, A. Barthelemy, K. Bouzehouane, S. Fusil, M. Varela, J. Fontcuberta and A. Fert, Phys. Rev. B 72, 020406(R) (2005) [2] M. Gajek, M. Bibes, S. Fusil, K. Bouzehouane, J. Fontcuberta, A. Barthelemy and A. Fert, Cond.Mat. 0606444 (2006) [3] H. Bea et al.; Appl. Phys. Lett., 88, 062502 (2006) and to be published in Phys. Rev. B.