We present improved processing of the soft amorphous ferromagnetic material for the fully integrated fluxgate magnetometer. The additional steps of polishing, chemical thinning and annealing are introduced to preserve the original material characteristics and increase the sensor fabrication yield. At the same time, due to the reduced thickness, the eddy current losses and skin effect are decreased. Hysteresis and power loss, as a measure of the magnetic material condition, are acquired after each processing step. Prepared material has at least 10-times better characteristics than electroplated NiFe. Presented procedure is compatible with the CMOS technology and implemented on a whole wafer in a batch process to form the cores for a low power magnetic sensor.