We have developed a method to improve the detection sensitivity for the magnetization M of magnetic nanoparticles (MNPs) using a high Tc superconducting quantum interference device magnetometer. The M response of MNP to an applied magnetic field H(M-H characteristics) can be divided into a linear region and a saturation region, which are separated at a transition point Hk. When applying an excitation ac magnetic field (Hac) and an additional dc bias field Hdc = Hk, the second harmonic of M reaches a maximum due to the nonlinearity of its M - H characteristics. This harmonic is stronger than any other harmonics, including a third harmonic. The advantage of using the second harmonic response is that the response can be measured even in a small field Hac. The M response of MNP was systematically analyzed and experimentally demonstrated. For conventional detection using a third harmonic, the amplitude of the Hac must be larger than the threshold level, which is almost the same as Hk. Detection methods using a second harmonic can be applied to magnetic particle imaging. We finally demonstrate the construction of a 1-D image of two separated bottle-shaped MNP samples using the method with a lock-in amplifier.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Electrical and Electronic Engineering