Polarized small-angle neutron scattering study of two-dimensional spatially ordered systems of nickel nanowires

Abstract

The magnetic and structural properties of two-dimensional spatially ordered systems of ferromagnetic nickel nanowires embedded into an Al 2 O 3 matrix have been studied using polarized small-angle neutron scattering (polarized SANS). We measured the total (nuclear and magnetic) scattering I(q) as a polarizationindependent scattering, the field-dependent scattering as I H (q) = I(q, H) À I(q, 0), where H is the magnetic field, and the nuclear-magnetic interference as a polarization-dependent (P) scattering ÁI(q, P). A typical scattering pattern is composed of the diffuse small-angle scattering and the Bragg peak. It is shown that the introduction of Ni into the matrix does not change the position of the Bragg peak but results in an increase of the scattering intensity both in the smallangle region and at the Bragg positions. An external magnetic field was applied perpendicular or parallel to the long dimension of the nanowires in order to reveal the anisotropic properties of the magnetic system. It is shown that, firstly, the magnetic-field-dependent scattering I H (q) provides new and principally different information as compared with the interference term ÁI(q). Secondly, two contributions to the interference term ÁI(q) (ascribed to the diffuse scattering and to the diffraction peaks) have different signs indicating different origins of the scattering objects. Thirdly, polarized SANS gives a detailed picture of the magnetization process, which could not be obtained by methods of standard magnetometry.

Magnetic small-angle neutron scattering

“…With typical dimensions of a few tens of nm in cross section, such structures still fit in the framework of nanomaterials (i.e., with two dimensions smaller than ∼ 100 nm). Magnetization reversal in aligned nanowire arrays has been studied using both polarized and unpolarized SANS, and spin misalignment is commonly observed (Grigoryeva et al, 2007;Grutter et al, 2017;Günther et al, 2014;Maurer et al, 2014). However, with a typical nanowire length approaching the micrometer range and usually oriented parallel to the neutron beam, arrays of magnetic nanowires act as a grating, and strong multiple scattering has to be taken into account depending on the nanowire length; this effect is discussed in depth in Grigoriev et al, 2010.…”

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

“…Magnetic SANS is a unique and powerful technique to investigate the magnetism of materials on the mesoscopic length scale of $1-300 nm [e.g. nanorod arrays (Grigoryeva et al, 2007;Gu ¨nther et al, 2014;Maurer et al, 2014), nanoparticles (Bender et al, 2019(Bender et al, , 2020Bersweiler et al, 2019;Za ´kutna ´et al, 2020;Kons et al, 2020;Ko ¨hler et al, 2021), INVAR alloy (Stewart et al, 2019) or nanocrystalline materials (Ito et al, 2007;Mettus & Michels, 2015;Titov et al, 2019;Oba et al, 2020;Bersweiler et al, 2021)]. For a summary of the fundamentals and the most recent applications of the magnetic SANS technique, we refer the reader to the literature (Mu ¨hlbauer et al, 2019;Michels, 2021).…”

The small-angle neutron scattering instrument D33 at the Institut Laue–Langevin

“…Polarized SANS experiments are becoming increasingly popular owing to intense interest in resolving magnetic structures and dynamics in areas such as ferrofluids (Bonini et al, 2007), magnetic nanoparticles (Disch et al, 2012), nanowire arrays (Grigoryeva et al, 2007), magnetic recording media (Wismayer et al, 2006), microstructure investigation of elemental metals and alloy systems (Heinemann et al, 2000), superconductivity and the vortex lattice (Laver et al, 2006), and chiral and skyrmion-like magnetic structures (Mü hlbauer et al, 2009). The insertion of an optional beam polarizer into a SANS instrument must be achieved using a device in transmission, such as a cell of polarized 3 He gas, or by reflection out of the beam of the unwanted spin state using a polarizing mirror.…”