Magnetometry Measurements of Nanomagnetic Materials

B.C. Dodrill
Lake Shore Cryotronics,
United States

Keywords: vibrating sample magnetometer (VSM), nanomagnetic materials, hysteresis, first-order-reversal-curves

Summary:

Magnetometers are used to characterize magnetic material properties. Magnetometry techniques can be broadly classified into two categories: inductive and force-based. The two most commonly used inductive techniques are vibrating sample (VSM) and superconducting quantum interference device (SQUID) magnetometry. Alternating gradient magnetometry (AGM) is the most often used force-based technique. The measurement most commonly performed to characterize a material’s magnetic properties is that of a major hysteresis loop. The hysteresis or M(H) loop is typically used to determine a material’s saturation magnetization Ms (the magnetization at maximum applied field), remanence Mr (the magnetization at zero applied field after applying a saturating field), and coercivity Hc (the field required to demagnetize the material). More complex magnetization curves covering states with field and magnetization values located inside the major hysteresis loop, such as first-order-reversal-curves (FORC), can provide additional information that can be used to characterize magnetic interactions and coercivity distributions in magnetic materials. Nanoscale magnetic materials (nanowires, nanoparticles, thin films, etc.) typically possess weak magnetic signatures owing to the small amount of magnetic material that is present. Thus, one of the most important considerations in determining which type of magnetometer is best suited to specific materials is its sensitivity as this determines the smallest magnetic moment that may be measured with acceptable signal-to-noise. Measurement speed, e.g., the time required to measure a hysteresis loop, is also important because it determines sample throughput, and it is particularly important for FORC measurements because a typical series of FORCs can contain thousands to tens of thousands of data points. The final consideration is the temperature and field range over which measurements are to be performed. In this presentation, we will present a fast, high sensitivity (less than 25 nanoemu) electromagnet-based VSM that has been designed for characterizing nanomagnetic materials over a broad range of temperatures (4.2K to 1,273K) and magnetic fields (> 3.2T), and we will present typical measurement results for various nanoscale magnetic materials.