Surface Roughness Effects on Magnetization Reversal of Magnetic Ring Elements
The effect of surface roughness on magnetoresistance of permalloy ring structure is investigated. Microstructured permalloy rings with surface roughness varying from 4.2 to 21 nm were fabricated using electron beam lithography and a chemical etching process. It is found experimentally that the first and second nucleation fields decrease obviously with the surface roughness increasing, and the field range for the flux-closure state is not associated with surface roughness. The results indicate that surface roughness in permalloy ring structure is an important factor that influences the magnetic behaviors of the ring. This result can provide important information for future designs of ring-shaped magnetic devices.
Alternating magnetic field assisted magnetization reversal in ferromagnetic antidot
Although the effects of high-frequency electromagnetic waves on magnetization reversal have been extensively studied, the influence of a low-frequency ac field on magnetization reversal has seldom been examined. In this study, we measured the magnetoresistance and examined the magnetic switching process of Permalloy antidot thin films under an alternating magnetic field with a frequency of 25 kHz. When no alternating magnetic field was present, the transitional field of the antidot thin films decreased as the angle of the direct magnetic field increased. When an alternating magnetic field was present, the transitional field exhibited the same trend. We compared the magnetization process of the antidot thin films with and without the alternating magnetic field and determined that the alternating field can facilitate the transition of magnetization, specifically, by lowering the transitional field with the highest variation rate (33.73%).
Evaluation of paramagnetic particles for use in a resonant coil magnetometer based magneto-immunoassay
This paper describes work that formed a part of an investigation to increase the detection sensitivity of a magneto-immunoassay. The study involved the characterisation of paramagnetic particles (PMPs) from a range of manufacturers in order to determine parameters that influence the assay sensitivity. Magnetisation curves were produced for each PMP type using a vibrating sample magnetometer. A resonant coil magnetometer which incorporated of a planar, spiral coil integrated with a phase locked loop based detector was used to investigate the effect of PMP number and mass on the resonant frequency of the coil. In order to compare performance in an assay using a resonant coil magnetometer, the sensitivity for a monolayer of particles was evaluated. The results enabled the identification of parameters that were critical for achieving maximum sensitivity and, of the particles studied, the 0.75 μm diameter PMPs demonstrated the greatest sensitivity in the resonant coil magnetometer.