Presentation Information
[P1-58]A New Perspective on Assessing the Magnetic Texture in Nd-Fe-B Magnets: The influence of coercivity
Luis Torres Quispe1, *Wagner Costa Macedo1, Marcelo Augusto Rosa1, Leonardo Antunes1, Apuniano Baldárrago-Alcántara1, Paulo Wendhausen1 (1. Federal University of Santa Catarina (Brazil))
Keywords:
Nd-Fe-B magnets,Texture determination,Magnetometry technique,Coercivity effect
Techniques like Xray diffraction and electron diffraction are commonly used to determine texture of rare earth magnets. However, these techniques have some disadvantages, such as requiring timeconsuming experiments, complex data analysis, a limited analysis volume compared to the size of an industrial magnet and higher infrastructure costs. The magnetometry technique is often used to determine the texture of NdFeB magnets and can offer significant advantages over diffractometrybased techniques. Fernengel et al 1996 were the first to propose this magnetometry technique for determining the texture of NdFeB magnets. However, the method was only applicable to highly textured magnets. Later, Quispe et al 2020 presented an improved version of Fernengels method, which is applicable for any degree of texture. Although this magnetometry technique is reliable in determining texture values in most rareearth magnets, it can introduce error when applied to magnets with coercivity values above 900 kAm. In this study, we propose a method that provides a coercivitydependent correction, allowing the magnetometry technique to remain a valid tool for magnets with any coercivity value.The methodology proposed here consists of determining the degree of alignment cosTheta from the values of the remanent magnetizations in the direction parallel Jr_parallel and perpendicular Jr_perpendicular to the magnets texture axis, for which it is necessary to work with a parallelepiped or cubicshaped magnet. The value of Jr_parallel is the easiest to obtain because the field applied by commercial pulse magnetizers are intense enough. On the other hand, obtaining Jr_perpendicular is more complicated, as fields greater than the anisotropy field would be required.Applying a magnetic field pulse in the xy plane can induce some permanent magnetization due to the contribution of misaligned grains randomly distributed throughout the magnet. Different ways to calculate the field induced by this pulse are analyzed. The mathematical expression used to calculate Jr_perpendicular in this newly proposed approach depends on the ratio F Hc_average H_pulsed where Hc_average is the average critical field for irreversible magnetization reversal, and H_pulsed is the pulsed field intensity and the angular distribution of magnetic moments P_sigma Theta Phi.To experimentally verify the proposed methodology, four magnets with different Hcj values were used. Magnet 1 Hcj 868 kAm, Magnet 2 Hcj 1047 kAm, Magnet 3 Hcj 1438 kAm and Magnet 4 Hcj 1895 kAm. The measured Jr_parallel values and the Jr_perpendicular values obtained using the proposed methodology allowed us to determine the degrees of alignment cosTheta_star for each magnet. From Magnet 1 to Magnet 4, these values were 973 percent, 977 percent, 881 percent and 948 percent, respectively. For comparison purposes, the degrees of alignment cosTheta were also calculated using the equation by Quispe et al 2020, yielding the following values from Magnet 1 to Magnet 4 976 percent, 990 percent, 900 percent and 998 percent. It is noted that for magnets with lower Hcj values, both approaches provide very similar cosTheta values. However, for magnets with higher Hcj, neglecting the effect of Hcj leads to an overestimation in the calculation of cosTheta, resulting in an absolute error of nearly 5 percent in the degree of alignment of Magnet 4. In magnets with even higher Hcj values, these errors may become more significant, emphasizing the importance of accounting for this effect.
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REFERENCES[1] J. Magn. Magn. Mater. 382, 219–224 (2015).[2] J. Magn. Magn. Mater. 157–158, 19–20 (1996).[3] J. Appl. Phys. 128, (2020).[4] J. Magn. Magn. Mater. 612, 172639 (2024).
