The AC material measurement has the potential to measure very small AC magnetic fields, and the AC property measurement can also provide material data with simultaneous AC frequency reporting and material-related losses.

High frequency Data

In sample measurements, the AC magnetic moment data derived from the AC applied field does not follow the DC magnetization curve for the same sample due to interactive, dynamic effects within the sample. In high AC frequency applications, the AC magnetization of the sample lags the applied field (driving field). In measurement, the AC ‘lagging effect’ is termed an AC loss factor and is one of the more important parameters associated with AC magnetic material measurements and their applications. The AC loss factor is reported as complex data.

AC Susceptibility measurements can be focused and localized while ‘Wide-band’ AC susceptibility measurements can also be made on samples whereby the resulting data employs an integrated reporting method for material property analysis over large frequency ranges.

Susceptibility, the focus of AC magnetometry measurements…

In AC magnetic measurements, where an AC field is applied to a sample and the resulting AC magnetic moment is measured, the resulting data is an important tool for characterizing magnetic materials. Because the induced sample’s magnetic  moment is time-dependent in the AC mode, resulting measurements yield information about magnetization dynamics which are not obtained in DC measurements.

Low to Mid-frequency Data

Low frequency AC magnetic measurement data is typically related to DC magnetometry results where the resulting magnetic moment of the sample follows the traditional DC magnetic, B-H curve measured with a DC (VSM) magnetometer[3]

[3]  Low frequency, Field induced AC magnetic moments typically follow the slope of the DC, B-H curve. The slope parameter reported as AC “susceptibility” and in DC terminology, reported as “permeability”.

Susceptibility & AC Loss Factor

Susceptibility vs. Temperature

Susceptibility vs. Driving Frequency

Susceptibility vs. DC Field Offset

Susceptibility vs. AC Field Amplitude, and Frequency Measurements

Susceptibility vs Induced Magnetization in Secondary Coils

Resistivity

Frequency Response

Critical Temperatures

Critical Current Density

Eddy Currents

The AC magnetic susceptibility can be also used to study magnetic relaxation

Susceptibility is used to characterize magnetic materials such as ferrites, Sendusts (FeSiAl materials),  semiconductors, superconductors and other magnetic materials where surface barriers and effects of granularity are of performance interest. The importance of correlating the AC susceptibility data with the materials’ intrinsic structure, is of interest for many applications, when AC magnetic data is combined with ARkival’s Atomic Force Microscopy (AFM) measurements.

Eddy currents are a cause of energy loss in many AC devices and their component materials. In DC devices, eddy current loss and hysteresis loss occur as Iron losses and are called core losses or magnetic losses.

Eddy currents have no direction and continually circulate in different conducting materials having ‘suitable’ cross sections for their presence. The magnetic flux (Moment) generated by the circular current motion generates an emf in the associated conducting surface and creates energy loss. Most important, Eddy currents typically dissipate their energy in the form of heat.

To reduce eddy current losses, wires are divided into separate strands and magnetic circuit components and shielding materials made from separate material sheets insulated from each other. The layer division into sheets placed at right angles to the direction of the eddy currents restricts the eddy current paths and reduces eddy-current losses. ARkival can perform eddy currents measurements and material analysis.