Magnetoresistive (MR) sensors are widely used in day-to-day applications, like in information storage applications, where the data are received from a magnetic hard disk with MR read sensor that is extremely sensitive to low magnetic fields, and magnetic sensing. The main aim of the MSCA project GRAMAS Nr. 751905 was to improve the sensitivity of magnetoresistive (MR) sensors to magnetic field by combination of two different materials. In the project, mixed-valence manganites Ln1-xAxByO3 (Ln = La, A = Sr, B= Mn, Co) were investigated and used for magnetic sensor applications due to the Colossal Magnetoresistance (CMR) phenomenon. However, several problems had to be solved concerning the usage of manganites for magnetic field sensing: MR anisotropy (MRA) of manganite films at fields < 0.3 T (limited by ‘shape’ or demagnetization effect), sensitivity to magnetic field at temperatures higher than room temperature (limited by Curie temperature), and sensitivity at fields close to megagauss which is limited by MR saturation of manganites. These problems are related to a very rich and complex physics of these manganites (due to the electron-lattice and electron-electron interactions in these layers) which then leads to the close relation of their structural, electric and magnetotransport properties. On the other hand, graphene layers can reach very large positive magnetoresistance values at intermediate and high magnetic fields (5-60 T), however, at low fields (<1 T) the sensitivity of graphene-based sensors is low due to classical quadratic MR dependence on magnetic flux density. Therefore, an innovative concept was suggested and applied: to combine manganite films with 2D graphene in order to improve the operational magnetic field range of magnetoresistive sensors.
The main/innovative objective was achieved by combining Graphene and novel manganite La1-xSrxMn1-yCoyO3 and showed the improved magnetoresistive behavior of the hybrid manganite-graphene structure for production of highly sensitive magnetic field sensors (Figure 1) operating at room temperatures in 0.1-20 T magnetic field range.
