Effect of deposition parameters on exchange bias studied using Lorentz and high resolution electron microscopy

Current theories for exchange bias (EB) do not satisfactorily predict the EB shift and enhanced coercivity prompting further experimental investigations. In previous studies, the effects of deposition parameters have been studied individually. In this work, the effects of four key parameters have been investigated: (a) type of antiferromagnetic (AFM) material (NiO and NiMn); (b) effect of annealing (No annealing and at 300 °C); (c) partial pressure of N₂ during permalloy (Py) deposition (0% and 7%s of total chamber gas pressure); and (d) presence or absence of Ta buffer layer. A 2^n-1-factorial design of experiments, where n is the number of variables, has been used to optimize the set of experiments. A total of 8 samples (=2^4-1 samples according to the design of experiments principles) were deposited in a magnetron sputtering chamber in a vacuum of 5 × 10-8 Torr. These were later field-cooled in a field of 150 Oe from a temperature of 300 °C to induce uniaxial magnetic anisotropy. Vibrating sample magnetometry (VSM) was used to plot the B-H curves of the samples. Rutherford backscattering spectroscopy (RBS) was used to confirm the thickness of the deposited bilayers. X-ray diffraction (XRD) θ-2θ scans were used to study the preferred orientation of growth. High-resolution electron microscopy and Lorentz microscopy have been used to correlate the microstructure and the micromagnetic behavior with the deposition parameters.