Unraveling the magnetic softness in Fe-Ni-B-based nanocrystalline material by magnetic small-angle neutron scattering.

Mathias Bersweiler,Kiyonori Suzuki,Michael P Adams,Inma Peral,Andreas Michels,Joachim Kohlbrecher

doi:10.1107/s2052252521010605

Mathias Bersweiler, Kiyonori Suzuki + Show 4 more

Open Access

https://doi.org/10.1107/s2052252521010605

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Abstract

Magnetic small-angle neutron scattering is employed to investigate the magnetic interactions in (Fe0.7Ni0.3)86B14 alloy, a HiB-NANOPERM-type soft magnetic nanocrystalline material, which exhibits an ultrafine microstructure with an average grain size below 10 nm. The neutron data reveal a significant spin-misalignment scattering which is mainly related to the jump of the longitudinal magnetization at internal particle-matrix interfaces. The field dependence of the neutron data can be well described by micromagnetic small-angle neutron scattering theory. In particular, the theory explains the 'clover-leaf-type' angular anisotropy observed in the purely magnetic neutron scattering cross section. The presented neutron data analysis also provides access to the magnetic interaction parameters, such as the exchange-stiffness constant, which plays a crucial role towards the optimization of the magnetic softness of Fe-based nanocrystalline materials.

Highlights

Since the pioneering work of Yoshizawa et al (1988), the development of novel Fe-based nanocrystalline soft magnetic materials raised considerable interest owing to their great potential for technological applications (Petzold, 2002; Makino et al, 1997)
The values of the lattice parameter a and the average crystallite size D were estimated from the X-ray diffraction (XRD) data refinement using the LeBail fit method (LBF) implemented in the FullProf suite (RodrıguezCarvajal, 1993)
The analysis of the magnetic small-angle neutron scattering (SANS) data suggests the presence of strong spin misalignment on a mesoscopic length scale

Summary

Introduction

Since the pioneering work of Yoshizawa et al (1988), the development of novel Fe-based nanocrystalline soft magnetic materials raised considerable interest owing to their great potential for technological applications (Petzold, 2002; Makino et al, 1997). This phenomenon has been successfully modeled within the framework of the random anisotropy model (RAM) (Herzer, 1989, 1990, 2007; Suzuki et al, 1998), and becomes effective when the average grain size D is smaller than the ferromagnetic exchange length L0 1⁄4 ’0ðAex=K1Þ1=2, where Aex is the exchange-stiffness constant and ’0 is a proportionality factor of the order of unity which reflects the symmetry of K1

Experimental

Unpolarized SANS

Approach-to-saturation regime

Estimation of the magnetic interaction parameters

Results and discussion

Conclusions