The goal of this research is to design and fabricate a very sensitive MEMS-based magnetic field sensor for space applications. The challenge is to reach the required sensitivity: measuring magnetic fields from a few nT to about 60000nT with sub-nano Tesla accuracy. The device studied in this paper is based on a classical resonating Xylophone Bar Magnetometer (XBM). It consists of a free-free beam supported in the nodal points of the fundamental transverse mode of vibration. A sinusoidal current at the vibration frequency is supplied via the nodal supports. In the presence of an external magnetic field, this current results in a sinusoidal Lorentz force that puts the XBM in vibration at its fundamental frequency. Two different materials are proposed to fabricate this device: the first one is Poly-SiGe and the second is Nickel. The paper will present multi-physics simulations to evaluate the response of the SiGe-XBM and the Ni-XBM. Following these studies, devices with several support lengths and shapes were designed and fabricated in poly-SiGe and Nickel. Increasing the quality factor by a dedicated design of the support and using the intrinsic properties of the material, the new magnetometer will have improved accuracy and resolution and will meet the requirements for space applications.