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Highlights • Thermal stability of H ex for MnPt and MnIr was studied in AF/FM bilayers and TMR stacks. • A model was developed to describe the H ex and H c behaviors at high temperatures. • A better thermal stability was observed in TMR stacks than bilayers. Abstract Ensuring a reliable reference in magnetoresistive devices requires robust exchange biased antiferromagnetic/ferromagnetic (AF/FM) bilayers with strong resilience to high temperatures. In this work, we studied the thermal stability of MnPt and MnIr by investigating the exchange bias effect in AF/CoFe bilayers and tunneling magnetoresistance (TMR) full stacks. In bilayers, the obtained blocking temperature ( T b ) of 380 °C for MnPt is higher than T b of 340 °C for MnIr, indicating a better thermal stability. Based on Malozemoff's model, we developed a comprehensive model to describe the exchange bias field ( H ex ) behavior at high temperature by considering the T b distribution and temperature dependence of FM magnetization, giving a good agreement with the experimental data. With increasing temperature, a coercivity ( H c ) enhancement peak was observed in MnIr bilayer, which shows a good agreement with T b distribution. This evidences the H c peak is dominated by the thermal activation of AF grains, indicating that the H c peak only appears at T b center , which is lower than overall T b . The structural properties and grain size of AF layers were studied by X-ray diffraction (XRD), where a mean grain size of 10.6 and 12.6 nm were obtained for MnPt and MnIr, respectively. Compared to bilayers, a more stable thermal behavior was observed in full stacks. In conclusions, our study compared the thermal stability of exchange bias coupling using MnPt and MnIr and developed a comprehensive model to study their temperature dependence. This proposed approach can be used for theoretical studies and experimental designs of AF-based materials for spintronic applications, such as magnetoresistive devices and high density memories. [ABSTRACT FROM AUTHOR]

Highlights • We study annealing effect on memory states stability in CoFeB/MgO/CoFeB based perpendicular MTJs. • Our study indicates a ferromagnetic coupling between the storage and reference layers. • Enhance pMTJs stability by playing perpendicular magnetic anisotropy and interlayer coupling. Abstract Perpendicular magnetic tunnel junctions (p-MTJs) attract great interest because of their excellent performance in spin-transfer-torque magnetic random access memories (STT-MRAMs). The annealing process is critical to achieve the required structural and magnetic properties, therefore obtaining high perpendicular tunneling magnetoresistance (p-TMR) and lower switching current. In this work, the CoFeB/MgO/CoFeB-based p-TMR stack was prepared and a high p-TMR value of 155.9% was obtained from CIPT. The p-MTJs were patterned with pillar sizes ranging from 50 nm to 1000 nm and were annealed upon different annealing temperatures (T A) of 300 and 340 °C. The resistance at parallel (R P) and antiparallel (R AP) state in p-MTJs was obtained upon the application of a ±30 mT perpendicular magnetic field, where the angle of magnetization between storage and reference layer at memory state, θ P and θ AP , were derived from the P and AP resistance ratios with and without magnetic field. The condition θ P = θ AP of about 63.5° was found in as-deposited samples, indicating a ferromagnetic interlayer coupling between storage and reference layers, where θ P = 0° and θ AP = 180° at T A = 300 °C and 340 °C demonstrate a stable memory state. The stability of the resistance state was modeled by considering the evolution of effective perpendicular magnetic anisotropy (K eff) and interlayer coupling constant (J), showing a method to evaluate the ratio of K eff / J via the memory state resistance characterization, where the K eff / J of about −1.26 was obtained in our as-deposited samples. Our study assesses the effect of T A on the θ P and θ AP and supplies the method to enhance the stability through the optimization of perpendicular magnetic anisotropy and interlayer coupling, so to better control the performance of p-MTJ-based STT-MRAMs. [ABSTRACT FROM AUTHOR]

• In highly sensitive magnetic sensors coupled to magnetic flux concentrators, the optimal operation point with maximum sensitivity may appear deviated from zero magnetic field. • Implementation of a magnetic bias technique (current line arrangement) which allows an efficient control of the operation point of the magnetoresistive sensor. • An optimum configuration of current lines placed on top of MFCs was successfully implemented within the requirements regarding the maximum current density targeting a maximum offset of 0.15 mT. • The final miniaturized device presents a centered branch of the curve around zero field and a high sensitivity suitable for ultra low field detection. In highly sensitive magnetic sensors coupled to magnetic flux concentrators, the optimal operation point with maximum sensitivity may appear deviated from zero magnetic field. Such characteristic can hamper the detection of very low magnetic fields. In this work a magnetic bias technique is presented which allows an efficient control of the operation point of the magnetoresistive sensor placed in the gap of two magnetic flux concentrators. Specifically, the magnetic field created compensates the shift of the output curve and is here generated by a current line directly integrated on chip. This method allows to control the input current and, therefore, change the local magnetic field towards a fine tuning of the offset field. The optimum configuration includes 44 current lines with 2.3 mA on top of each magnetic flux concentrator yielding a shift of 0.1 mT. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic sensors based on the planar Hall effect of exchanged-biased permalloy have been fabricated and characterized. It is demonstrated that the sensors are feasible for detecting just a few commercial 2.0μm magnetic beads commonly used for bioseparation (Micromer-M, Micromod, Germany) and that the sensor sense current is sufficient to generate a signal from the beads. [Copyright &y& Elsevier]