Magnetic Guinier Law

III. Theory

Magnetic Guinier Law

A. Malyeyev and A. Michels

Physics and Materials Science Research Unit, University of Luxembourg,

162A Avenue de la Faïencerie, L-1511 Luxembourg, Grand Duchy of Luxembourg

[1] D.I. Svergun and M.H.J. Koch, Rep. Prog. Phys. 66, 10 (2003).

[2] D. Honecker and A. Michels, Phys. Rev. B 87, 224426 (2013).

[3] A. Michels, J. Phys. Condens. Matter. 38, 26 (2014); S. Mühlbauer et al., Rev. Mod. Phys. 91, 015004 (2019).

[4] J. Weissmüller et al., Phys. Rev. B 63, 214414 (2001).

[5] J.-P. Bick et al., Appl. Phys.Lett. 102, 022415 (2013).

[6] X. Guo et al., Phys. Rev. B 46, 14578 (1992).

[7] S. Muralidhar et al., Phys. Rev. B 95, 024413 (2017).

We acknowledge the financial support from the Fonds National de la Recherche Luxembourg (AFR Individual 12417141).

We introduce the Guinier law for the case of magnetic SANS and provide an analysis of experimental data on a Nd-Fe-B-based nanocomposite and on a rare-earth-free MnBi permanent magnet. The robustness of this novel approach is discussed and the quantities derived are analyzed in the framework of the existing research literature.

IV. Experimental Results

V. Summary

References I. Introduction

II. Nuclear SANS

III.1

III.2

III.3

We have introduced the magnetic Guinier law on the conceptual level and tested the robustness of the procedure using magnetic SANS data of a Nd-Fe-B-based and rare-earth- free MnBi permanent magnet. In both cases, the obtained values of the exchange stiffness constant are in perfect agreement with existing data in the literature and the radius of gyration of the magnetic anisotropy field was demonstrated to be comparable with the particle size of the nanocrystaline magnet. A broad range of experimentally accessible internal fields is of paramount importance for the subsequent numerical analysis.