Ultra-soft magnetic properties in Ta/NiFe laminated system

Abstract

An integrated magnetic flux concentrator (MFC) has become a choice for enhancing the sensitivity of a magnetic field sensor. However, the flux concentrator’s geometry and its ultra-soft magnetic properties are the key ingredients for successful implementation to improve the detectability of a magnetic sensor. In this report, the laminated stack of Ta/Ru/[NiFe(tNiFe)/Ta(tTa)]N/Ta of thickness 0.5 μm was investigated, where tNiFe, tTa, and N were varied to optimize ultra-soft magnetic properties of the film and compared them with the bulk NiFe film. Structural investigations revealed that incorporating an ultra-thin layer of Ta in the laminated stack suppresses the grain growth of the NiFe phase and improves the textured growth of the fcc(111) phase of the NiFe alloy. This results in dramatic improvement of the measured magnetic hysteresis loop of the laminated stack with a reduced coercivity field in the range of 0.4 ± 0.1 Oe, high linearity, and low saturation field (<10 Oe) while comparing them with the bulk film of NiFe of equivalent thicknesses. The laminated stack thickness of up to 4 μm was further investigated, and the bilinear M(H) loop was explained through antiferromagnetic (AFM) interlayer coupling between successive NiFe layers.