Roughness influence in the barrier quality of ferroelectric/ferromagnetic tunnel junctions, model and experiments

M. SIRENA, J. GONZALES SUTTER, L. AVILÉS FÉLIX ; L.B.STEREN; R. BERNARD, J. E. VILLEGAS, J. BRIÁTICO; , N. BERGEAL,A. ZIMMERS, J. LESUEUR; G. FAINI

Barcelona

Conferencia; International Conference on Magnetism; 2015

Manganites have attracted a lot of attention due to the possibility of studying many physical problems related to the strong correlation between their structural, transport and magnetic properties and their potential use in many technological applications. A renewed interested in these compounds has appeared for the developing of manganite/ferroelectric composite systems with multiferroic nature. The origin of this interest is the possibility to develop new technological devices, such as ferromagnetic/ferroelectric tunnel junctions (TJ), with new flexibility and improved performance. In order to obtain systems with increasing reading rate and low head noise, very thin tunnel barriers are required and a good knowledge of the barrier characteristics becomes critical. Recently, conductive atomic force microscopy (CAFM) has become an important tool to characterize the tunnel barrier for TJ like devices (such as spin filters, superconducting Josephson Junctions, etc.).In this work a phenomenological approach has been developed to analyze the electrical transport through an insulating barrier in ferromagnetic/ferroelectric bilayers, using CAFM. We have found that I(V) = A0 . V^alpha , where A0 and alpha depend linearly with the barrier thickness. The model allows to obtain critical information for the development of magnetic TJ. Moreover, assuming a Gaussian distribution of the barrier thickness, it is possible to fit the measured current distribution and to study the thickness homogeneity of the barrier. The influence of the substrate in the electrical properties of the FE/FM bilayers was studied in the frame of this model. CAFM images of both series of samples present an important distribution of the current, which is generally ascribed to a distribution in the barrier thickness. However, MGO substrates with higher roughness were found to increase the barrier height distribution and increase the attenuation length in the material, reducing the barrier quality for the developing of multiferroic tunnel junctions.