High-Temperature Magnetic Tunnel Junction Magnetometers Based on L1₀-PtMn Pinned Layer

Magnetometer sensors with high sensitivity based on magnetic tunnel junctions (MTJs) were developed to operate at high temperatures of more than 250 °C. We replaced the commonly used IrMn antiferromagnetic pinning layer with an optimized PtMn antiferromagnet, which has a high magnetic thermal stability due to its L1₀ crystal structure. We investigate the effect of measurement temperature on magnetoresistance (MR), exchange bias, and sensitivity in sensor MTJ stacks using either IrMn or PtMn pinning layers. Upon increasing the temperature up to 250 °C, the MR ratio decreases from 146% to 50% for IrMn, and 133% to 80% for PtMn pinning layers. The PtMn-based MTJ sensors sustain a constant sensitivity (4-5 %/Oe) up to 250 °C, compared with IrMn-based sensors, which decrease drastically. This high-temperature performance links to the thermal stability of exchange bias in the pinned layer by using PtMn.