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Magnetic nanoparticles (MNPs) are physically immobilized in some biomedical applications. In this case, dynamic ac magnetization that determines MNPs’ performance has strong dependence on the relative direction between the magnetic easy axes of MNPs and the applied excitation field. To study this dependence, we prepared immobilized MNP samples with different degrees of easy axes’ alignment. The degree of alignment was changed by setting the strength of a dc field that is applied during the immobilization process. The magnetic properties of these samples, such as ac magnetization, coercive field, amplitude of third-harmonic signal, and hysteresis loss, are compared with those of a randomly oriented easy axes’ sample. It was shown that these values are significantly affected by the degree of easy axes’ alignment when the strength of the ac excitation field, $H_{0}$ , is relatively small. The alignment effect gradually becomes smaller when $H_{0}$ is increased. These findings are important for immobilized MNP applications in hyperthermia and magnetic particle imaging. [ABSTRACT FROM AUTHOR]

The magnetic core-size distribution of magnetic nanoparticles (MNPs) was estimated from three independent measurements, i.e., magnetization, ac susceptibility (ACS), and magnetic relaxation (MRX). First, distribution of magnetic moment m in MNP sample was estimated by analyzing the static magnetization ( M – H) curve of the MNP sample in suspension. Next, distribution of anisotropy energy E was estimated by analyzing the ACS of immobilized MNP sample measured from 10 Hz to 1 MHz. The ACS measurement in much lower frequency range was substituted by the MRX measurement. MRX of immobilized MNP sample was measured from 2 to 10^4 s, corresponding to the frequency range from 10^-4 to 0.5 Hz in ACS measurement. The relaxation curve was analyzed using a newly developed analytical method to estimate the E distribution of the MNPs in the range of large E values. Then, the estimated distributions of m and E were transferred to the distributions of magnetic core size. Core-size distributions obtained from m and E distributions reasonably agreed with each other. Namely, we obtained similar core-size distribution from static and dynamic properties of MNP sample, confirming the validity of the present method. Therefore, the present method can be useful to estimate the core-size distribution of MNP sample. [ABSTRACT FROM AUTHOR]

A novel method for constructing an integrated gradiometer and a magnetometer is proposed based on fundamental mode orthogonal fluxgate operation. In the integrated sensor construction, the summation of both sensor head outputs is used for the magnetometer operation and the subtraction of them is used for the gradiometer operation. The baseline separation distance between the sensor heads is adjustable. The sensor heads pair can be configured either axially or in parallel. Experiments were conducted with axial configuration of 5 cm baseline to show the selective detection capability to gradient and homogeneous magnetic field. The sensing system presented can be used to measure the average and the gradient of input magnetic field and its interesting applications are the gradiometric sensing of magnetic field distribution anomalies in a relatively large homogenous magnetic field interference. [ABSTRACT FROM AUTHOR]