Strontium ferrite/polyamide12 (PA12) magnetic composite fused deposition modeling filaments made using a twin-screw extruder are being studied to be used for Magnetic Field Assisted Additive Manufacturing (MFAAM) of permanent magnets. A previous study shows that the magnetic viscosity (MV) varies with field and field angle. The Mx MV is maximum in the easy plane (1.1%) and decreases with a factor of two along the filament’s macroscopic hard axis [1]. The My MV is nearly zero along the hard axis and in the easy plane but maximum for intermediate angles. Here we study the time dependence as a function of temperature using a MicroSense EZ9 biaxial VSM to determine the melt viscosity. Samples were made by loading ~14 mg of SrO(Fe2O3)6/PA12 (26 or 40 wt%) cylindrical-shaped filament parts in pyrex glass tubes. The filament is compacted with PEEK stoppers on both sides to secure its position and avoid direct exposure to the atmosphere while heating. Our aim is to study the rotation of the magnetic particles in the molten PA12 matrix. We first heat the sample to 200 oC to orient all the particles in the y-direction using a field of 22 kOe. Then the sample temperature is lowered to the target temperature after which the field is lowered to zero. Finally, a field step is applied in the x-direction and Mx and My are monitored as a function of the time. The rotation of the moment vector with time is calculated from the data. Measurements are done for the fields of 500 and 2000 Oe, and at the temperatures of 120, 124, 128, 132, and 136°C. Up to 128°C, no strong time dependence was observed. Between 128 and 132°C, the magnetic particles orientations are no longer fixed in the matrix, but they can rotate and line up along the field direction. The time dependence of the rotation of the magnetic particles in the PA12 matrix is calculated from Mx and My (Fig. 1 and Fig. 2). The time constant decreases with temperature and field. The melt viscosity of the molten PA12 matrix at 136 oC is determined from the data is 1.4E5 Pa.s at 500 Oe field.

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Time Dependence Analysis as a Function of the Temperature of Magnetic Polymer Composite Filaments

Strontium Ferrite magnetic nano-powder is being studied to be applied in magnetic 3D printer filament. Here we report on a study of the time dependence of its magnetic properties to better understand the permanent magnetic moment per unit volume of a nanocomposite containing the material [1,2,3]. Samples were made by loading up to 30 mg of OP-71 from Dowa Electronics Materials Company in a cylindrical custom design powder sample holder. Isotropic and anisotropic samples were made by loading the material in 0 field or in a field of 22,000 Oe. After loading the powder, the samples were compacted by compressing the powder along the cylindrical access. The typical samples were cylinders with a diameter of 2.5 mm and a length of 3 mm. The magnetic hysteresis curves of the samples were measured with a biaxial MicroSense Vibrating Sample Magnetometer (VSM) as a function of the field angle. For the isotropic samples, the average coercivity and the Mr/Ms were approximately constant as a function of the field angle for the Mx signal and were respectively 3402.35 Oe and 0.49. The shape of the Mx-hysteresis curves was independent of the field angle. For the anisotropic samples, the coercivities were around 3455 Oe (Mx curves). The Mr/Ms of the anisotropic samples depends on the field angle and varies from 0.41 along the hard axis to 0.64 along the easy axis. The coercivity of the My curves is around 4373 Oe. The coercivity of the anisotropic data seems to be larger than that of the isotropic sample due to the orientation of the crystallites. The time dependence of the Mx /Ms and My/Ms signals after a field step from saturation were measured for both the isotropic and anisotropic samples. The time derivative of the magnetization normalized on the Ms (S) depend on the field magnitude and shows a maximum. For the Mx signal this maximum coincides with the sample’s coercivity. The S(H) for the anisotropic curve for the My signal is shifted to larger fields as shown in the graph below. This work was supported in part by NSF through an DMR-MRI Grant under Award 1726970.References: [1] reference of strontium ferrite, maybe original philips patent. [2] R. Street, J. C. Wooley, Proc. Phys. Soc. London, Sect. A 62 (1949) 562. [3] L. Neel , Ann. Geophys. 5 (1949) 99.

Time Dependence of Magnetic Moment of Strontium-Ferrite Powder Measured by Biaxial VSM

**Session chairs:** Isabelle de Moraes, Institut Jean Lamour, Université de Lorraine and Jeffrey Shield, University of Nebraska-Lincoln



DOD - Advanced Processing of Permanent Magnets

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L3: Magnetization Dynamics and Damping III

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Tanjina Nasreen Ahmed

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Time Dependence Analysis as a Function of the Temperature of Magnetic Polymer Composite Filaments

Time Dependence of Magnetic Moment of Strontium-Ferrite Powder Measured by Biaxial VSM

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