Development of two axes magnetometer for navigation applications

Anisotropic Magneto resistance (AMR) effect offers significant potential for the fabrication of low field magnetic sensors as it lends well to the Earth’s field sensing range. To operate the sensor in linear and low field regions, theoretical simulation with optimized barber pole biasing configuration was carried out and implemented to our device fabrication. Permalloy based AMR film was characterized with a magnetoresistive coefficient of 2% and then barber pole biased AMR sensor was developed to obtain a linear transfer curve with sensitivity 0.35(mV/V)/G. Further, the design was extended towards the development of two axes magnetometer and the study was concluded with the indoor calibration of magnetometer utilizing a Helmholtz coil magnetic simulator

A novel AMR based angle sensor with reduced harmonic errors for automotive applications

The paper presents the development of a novel anisotropic magnetoresistive sensor for measurement of angle in the interval 0° to 180°. A sensor is comprised of two Wheatstone bridges arranged at 45° to each other. A unique design is proposed wherein each resistive element of the Wheatstone bridge was formed with strips of varying widths. It results in a substantial reduction in harmonics errors due to the dispersion of the shape anisotropy field values within each element. The reduced harmonic errors also lead to a drastic reduction of hysteresis error (60%) and offer better accuracy with a signal amplitude of 18 mV/V even in weak fields of ≤80 G. Further, the sensor was employed in the development of a pedal position sensor. The preliminary results of the development are presented, indicating the usability for industrial and automotive applications

MgO based specular spin valve with reversible minor loop and higher exchange bias for futuristic linear magnetic field sensor

Specular spin valves (SVs) containing ultrathin MgO, structured as substrate/seed/AF/PL1/MgO/PL2/Cu/FL/MgO/cap, have been fabricated. Both structural and magnetic characterizations of MgO based specular spin valve (SSV) have been performed and compared them with the measured data on naturally oxidized (NO) and conventional spin valves (CSV), grown under optimised condition. Reversible minor loop characteristics, highest exchange bias of 625 G and 10% magnetoresistive (MR) ratio were important observations in MgO based system. Zero hysteresis behavior was confirmed due to the reduction of grain growth of the stacks above the fine-textured MgO layer, through X-ray diffraction measurements. Interestingly, at 10 K, above 100% enhancement in MR ratio was observed in MgO based system with marginal increase in coercivity of the order 1 G. On the other hand, NO based structure has 10% MR, minor loop hysteresis of 2 G and exchange bias of 560 G at room temperature; however at 10 K, only 75% enhancement in MR ratio with large anomalies in magnetic measurements attributes due to the AFM nature of oxide materials. The above studies reflects the superior performance of MgO based SSV over a wide range of temperature in comparison to other SV structures and may lead to futuristic linear magnetic field sensor applications

Evolution of magnetoresistance behaviour at low temperatures in naturally oxidised specular spin valve systems

The temperature dependent magnetoresistive behaviour of field cooled naturally oxidised specular spin valve systems has been studied in the temperature range of 300–10 K. Inconsistent to the non-specular spin valve system, an anomalous behaviour was evolved with large exchange bias and higher coercivity, below 200 K. The structural investigations inferred the formation of magnetic oxides with higher density gradient in the pinned layer, and the observed anomalous behaviour at low temperatures was correlated with the antiferromagnetic ordering of these oxides in spin glass state. The uncompensated interfacial magnetism of the nano-oxide layer was further confirmed by comparing with low temperature magnetoresistive behaviour of non-magnetic oxide based specular spin valve systems