Irreversible relaxation behaviour of a general class of magnetic systems

Abstract. It is shown that magnetic systems after magnetization in a weak external field for a finite time t mag exhibit a universal time-dependent relaxation behaviour. The normalized magnetization decay after switching off an external field does not depend on any sample parameters and follows a universal law m(t) ∼ log(1 + t mag /t). This universal time dependence is confirmed by magnetic relaxation measurements performed on different powders of small barium hexaferrite magnetic particles at room temperature. The measurements were performed using the PTB SQUID magnetometer in the Berlin Magnetically Shielded Room

Gastrointestinal Transit of a Magnetically Marked Capsule Monitored Using a 37-Channel SQUID-Magnetometer

The gastrointestinal transit of magnetically marked solid pharmaceutical drug dosage forms can be monitored using biomagnetic measurement equipment. The presented study shows that using a 37-channel SQUID-magnetometer the investigation of the gastrointestinal transit of an ingested magnetically marked capsule becomes feasible with a temporal resolution in the order of milliseconds and a spatial resolution in the millimeter range

Giant Magnetoresistive Biosensors for Time-Domain Magnetorelaxometry: A Theoretical Investigation and Progress Toward an Immunoassay

Magnetorelaxometry (MRX) is a promising new biosensing technique for point-of-care diagnostics. Historically, magnetic sensors have been primarily used to monitor the stray field of magnetic nanoparticles bound to analytes of interest for immunoassays and flow cytometers. In MRX, the magnetic nanoparticles (MNPs) are first magnetized and then the temporal response is monitored after removing the magnetic field. This new sensing modality is insensitive to the magnetic field homogeneity making it more amenable to low-power portable applications. In this work, we systematically investigated time-domain MRX by measuring the signal dependence on the applied field, magnetization time, and magnetic core size. The extracted characteristic times varied for different magnetic MNPs, exhibiting unique magnetic signatures. We also measured the signal contribution based on the MNP location and correlated the coverage with measured signal amplitude. Lastly, we demonstrated, for the first time, a GMR-based time-domain MRX bioassay. This approach validates the feasibility of immunoassays using GMR-based MRX and provides an alternative platform for point-of-care diagnostics