Study of Systematic Error in Biaxial Torque, and Magnetic Characterization of Strontium Ferrite

Magnetic anisotropy (MA) describes how the magnetic properties of materials, such as ferri- and ferromagnetic thin films and composites, change with the field angle. To determine a sample’s magnetic anisotropy constant, torque curves are used, obtained either directly with a torque magnetometer (TM) or indirectly with a vibrating sample magnetometer (VSM). While most TMs operate only at room temperature, a biaxial VSM can measure torque at various temperatures. VSM torque curves often show a 2θ background due to sample misalignments or asymmetry, caused by the sensitivity matrix's position dependence of the VSM pickup coil-set. This thesis investigates the magnetic torque of 3D-printed strontium ferrite/PA-12 samples using a biaxial VSM and compares these measurements with those from a torque magnetometer. Torque curves were recorded from 16-22 kOe at 2 kOe intervals for a 4.8 mm wire and a 1.23 mm dot sample using a MicroSense EZ9 VSM. Fourier analysis determined the second harmonics from each torque curve. The wire samples’ biaxial torque curves showed a larger torque amplitude background due to Y-coil cross-talk, stemming from the sample's asymmetry and misalignment on the sample-holder. Background interference can be minimized by using cylindrically symmetric samples and precise mounting. The magnetic anisotropy constants determined from the torque curves measured with the TM slightly depend on the sample size and shape. A model was developed to describe the torque exerted on the sample by the image dipoles of the pole pieces. A 2 component is present in the torque curve even for a perfectly centered sample. The centering of the sample is also expected to affect the torque though. Direct measurements using a permanent magnet in zero field show however that the image effect might be smaller than 0.120 dyne.cm for a sample with a magnetic moment of 1.3 emu. In addition, the effect of the sample’s stray field on the field sensor however can also contribute to a background in the torque curve. Furthermore, the 3D printed strontium ferrite sample was characterized through VSM to investigate the coercivity and magnetic anisotropy for different field directions. It was noticed that the easy axis of the 3D printed samples was at an oblique angle in between the print-bed normal and the extrusion direction.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Physics

Grantor

Texas State University

Year dc:date.issued

2024

Author dc:creator

• Sapkota, Arjun

Advisor dc:contributor.advisor

• Geerts, Wilhelmus Johannes Maria Arnoldus

Committee members dc:contributor.committeemember

• Miyahara, Yoichi
• Tate, Jitendra S.

• VSM
• Strontium ferrite

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10877/19290

OAI identifier oai:identifier

oai:digital.library.txst.edu:10877/19290