Park Knowledge Portal

Speaker : Kevin Dalla Francesca Affiliation : CEA Saclay, France Region : Europe Year : 2022 Language : English Local magnetic characterization is a key approach to investigate magnetic nanomaterials used in the area of electronics, sensors or health application. The project presented consists in developing a local magnetic probe microscope, able to perform quantitative and ultra-sensitive (nanoTesla) measurements of magnetic stray fields and topography of a sample with a lateral resolution of the order of a hundred nanometers at room temperature. The MagnetoResistive-Scanning Probe Microscopy (MR-SPM) combines a giant magnetoresistance (GMR) sensor and a local probe microscope. The GMR sensor is integrated into a flexible cantilever and allows the measurement of magnetic field emitted by the sample while the deflection of the cantilever gives information about the surface topography as shown in Figure 1. Currently a number of characterization tools are available such as MFM (Magnetic Force Microscopy) or local probe microscopy by NV (Nitrogen Vacancy) center [1-3]. MR-SPM allows realization of simple quantitative measurements with a detectivity around 40 nT/Hz-1/2 and with a low resolution of the order of 100 nanometer but which remains higher than the resolution reached by other techniques like the one quoted above. However, the main advantage of the MR-SPM is the possibility to measure magnetic susceptibility (up a frequency of 100MHz) of a surface by applying an AC field thanks to a coil positioned around or under the sample. The GMR sensor, based on spin electronics, is composed schematically of two thin ferromagnetic layers separated by a non-magnetic and conductive layer (spacer). A ferromagnetic layer called "free layer" has a magnetization that follows the direction of the magnetic signal to measure. The second ferromagnetic layer has a magnetization that remains fixed (“reference layer”). The resistance of the stack varies according to the relative angle between the magnetizations of these two layers. The use of a complex stack as shown in figure 2 allows to obtain a linear variation of the resistance around zero field before saturation. An important point of the work is the fabrication of flexible cantilevers incorporating a magnetoresistive sensor with a characteristic size of several micrometers. The fabrication requires a combination of optical and laser lithography steps, linked to physical and chemical etching, and deposition by evaporation and sputtering. We will show recent development concerning the fabrication of sensors integrated in the cantilevers, the reduction of the GMR-surface distance to improve the lateral resolution and the characterization of the magnetoresistance properties of the GMR tips. Validation measurements of MR-SPM on calibration samples will be presented as well as the first images on magnetic particles and on magnetic nanocrystalline tape. [1] S. J. Bending, Advances in physics, 1999, vol. 48, issue n° 4, p. 449-535 [2] H. Corte-León, V. Neu, A. Manzin, C. Barton, Y. Tang, M. Gerken, P. Klapetek, H. Werner Schumacher, O. Kazakova, small, 2020, vol. 16, issue n°11 [3] K. Mizuno, M. Nakajima, H. Ishiwata, et al. AIP advanced, 2018, Vol. 8