Dynamic Hysteresis Measurement of Magnetic Nanoparticles with Aligned Easy Axes

Abstract

Magnetic particle imaging (MPI) is a novel diagnostic imaging technique based on the use of magnetic nanoparticles (MNPs). Investigating the magnetic properties of magnetic nanoparticles is important for achieving a high spatial and temporal resolution in MPI. In this study, -Fe2O3 nanoparticles (core diameter: dc = 4 nm), Fe3O4 nanoparticles (dc = 20-30 nm), and Resovist ® were immobilized in a DC magnetic field with their easy axes aligned. DC and AC magnetization curves were measured for the prepared MNPs. The measurements were performed by applying fields parallel and perpendicular to the easy axis and evaluating the magnetic properties of the MNPs for the easy and hard axes. The direction of magnetic moments under the AC magnetic field applied to the direction of the easy axis or hard axis was evaluated by using both experimental results and numeric simulation using the Landau-Lifshitz-Gilbert equation to reveal magnetic relaxation property at wide frequency range and the effect of core size distribution of oriented MNPs. The effect of anisotropy in superparamagnetic nanoparticles, the relaxation property depending on the anisotropy energy barrier, and the fast magnetization process of Néel relaxation were successfully observed.

Enhanced specific loss power from Resovist® achieved by aligning magnetic easy axes of nanoparticles for hyperthermia

“…The increasing tendencies of the coercive field in the easy axis and hard axis samples are similar to those in the magnetic field intensity of 4 kA/m. We observed the change in the orientation of the magnetization by the numerically simulation with regard to the MNP in core diameter of 5±2 nm (mean±SD), when the field intensity was changed from -16 kA/m to 16 kA/m at the field frequency of 100 kHz 11) . Our numerical simulation revealed that the magnetization is oriented to the opposite direction of the applied field without reversal in the easy axis sample because of the anisotropy toward the easy axis.…”

“…Figure 1 (a-d) shows the samples for experiment. The intensity of the DC field during the preparation of the samples with aligned easy axes was 575 kA/m 11) .…”

“…To achieve a high SLP, the magnetic properties of Resovist ® need to be investigated, and optimal conditions related to the applied field and the parameters of Resovist ® should be determined. In this study, we fabricated samples of Resovist ® with oriented easy axes 10,11) and measured their magnetic properties. The orientation of the easy axes should be considered for MFH applications wherein an AC magnetic field is employed for diagnosis.…”

Magnetization Characteristics of Oriented Single-Crystalline NiFe-Cu Nanocubes Precipitated in a Cu-Rich Matrix

“…Therefore, the magnetocrystalline anisotropy was not observed during the dynamic magnetization process in this measurement under H AC = 4 kA/m. The anisotropic features in a dynamic magnetization process are observed when the magnetic field larger than the anisotropy energy is applied to the samples [ 11 , 37 , 38 , 39 ].…”

Dynamics of Magnetization and Easy Axis of Individual Ferromagnetic Nanoparticle Subject to Anisotropy and Thermal Fluctuations

“…1(c). With decreasing θ, the magnetization distribution was strongly aligned along the direction of the applied field, owing to the reduced anisotropy energy barrier 9),32), 33) . Two nodes connected by a line show the continuous trajectory of the magnetization in Fig.…”