Co site preference and site-selective substitution in La–Co co-substituted magnetoplumbite-type strontium ferrites probed by ⁵⁹Co nuclear magnetic resonance

Abstract

In the La-Co co-substituted magnetoplumbite-type strontium (Sr-La-Co) ferrite, the base materials of the high-performance hard ferrite magnet, Co tends to occupy more than two crystallographically inequivalent sites. To reveal the Co site preference and the function of each site, 59 Co nuclear magnetic resonance (NMR) spectrum was measured for the Sr-La-Co ferrites with various Co compositions. The intimate correlation between the anisotropy field and the relative intensity of the strongest NMR line clearly indicates that Co occupying the tetrahedrally coordinated 4f 1 site is only responsible for the enhancement in the uniaxial anisotropy. In the samples with the Co concentrations much larger than commercial magnets, most Co selectively occupies the 4f 1 site, indicating possible tuning of the magnetic performance with limited Co content in the future development. The close correlation between orbital moments and local strain is also demonstrated.

Nuclear magnetic resonance in ferromagnets: Ferromagnetic nuclear resonance; a very broadband approach

“…When the external RF field H1 is applied, the resulting rotation dθ of the electronic magnetisation induces a rotation dφ of the HF which produces a field component H1* = HF dφ perpendicular to HF (see Figure 1). The enhancement factor is thus written as η = HF (dφ / dθ) (dθ / dH1) (9) Note that here no assumption is made about the respective orientations of HF and of the electronic magnetisation (φ and θ may be different).…”

“…During the last 3 decades this broadband approach has been used to study a large variety of samples [1][2][3], bulk samples [4][5][6][7][8][9][10], magnetic multilayers and thin films , assemblies of nano-objects [52][53][54][55][56][57][58][59][60][61][62]. It allowed to give contributions into various research fields: spintronics, hard magnets, multi-layered mirrors, heterogeneous catalysis etc.…”

Single crystal synthesis and magnetic properties of Co2+-substituted and non-substituted magnetoplumbite-type Na–La ferrite

“…The second mechanism for the contribution of non-magnetic A site ions to MA is via the alternation of Co 2+ site preference. As revealed by NMR spectroscopy, Co 2+ ions are non-uniformly distributed over the 2a-O, 4 f 1 -T and 12k-O sites, and mainly located on the 4 f 1 -T site [20]. Since H A is correlated with the concentration of Co 2+ on the 4 f 1 -T site, Co 2+ on the site contributes to uniaxial MA.…”

Revealing the morphology and the magnetic properties of single buried cobalt-ZnTPP hybrid interfaces by ferromagnetic nuclear resonance spectroscopy

“…information is seldom extracted from the FNR data, but recently it was successfully used to understand the origin of the increase in anisotropy of permanent magnets doped with Co [32]. This approach allows to probe the magnetic anisotropy field of the Co atoms at the interfaces with respect to the magnetic anisotropy of the bulk (the inside) of the Co layers.…”