Influence of structure and cation distribution on magnetic anisotropy and damping in Zn/Al doped nickel ferrites

Abstract

An in-depth analysis of Zn/Al-doped nickel ferrites grown by reactive magnetron sputtering is relevant due to their promising characteristics for applications in spintronics. The material is insulating and ferromagnetic at room temperature with an additional low magnetic damping. By studying the complex interplay between strain and cation distribution their impact on the magnetic properties, i.e., anisotropy, damping, and g-factor is unravelled. In particular, a strong influence of the lattice site occupation of Ni 2+ Td and cation coordination of Fe 2+ Oh on the intrinsic damping is found. Furthermore, the critical role of the incorporation of Zn 2+ and Al 3+ is evidenced by comparison to a sample of altered composition. Specifically, the dopant Zn 2+ is evidenced as a tuning factor for Ni 2+ Td and therefore unquenched orbital moment directly controlling the g-factor. A strain-independent reduction of the magnetic anisotropy and damping by adapting the cation distribution is demonstrated.

Control of site occupancy by variation of the Zn and Al content in NiZnAl ferrite epitaxial films with low magnetic damping

“…In the ideal case Ni only occupies B sites and Fe sits in * Electronic address: julia.lumetzberger@jku.at; Phone: +43-732-2468-9651; FAX: -9696 a 1:1 ratio on the A and B sites. However as previously reported [3,4], due to the growth on a normal spinel substrate MgAl 2 O 4 (001) and by introducing the two additional elements Zn and Al a mixed spinel is the result. Therefore, Ni can be considered to also occupy tetrahedral sites and additionally Fe 2+ Oh was found to be introduced into the system [3,4].…”

“…However as previously reported [3,4], due to the growth on a normal spinel substrate MgAl 2 O 4 (001) and by introducing the two additional elements Zn and Al a mixed spinel is the result. Therefore, Ni can be considered to also occupy tetrahedral sites and additionally Fe 2+ Oh was found to be introduced into the system [3,4]. In addition to this complex interplay of several elements with different valencies, charge neutrality has to be considered as well, and small deviations can be compensated to some extent by the formation of oxygen vacancies.…”

“…From this an in-plane lattice parameter of a = (8.08 ± 0.01) A identical to the lattice parameter of the cubic MgAl 2 O 4 substrate is obtained. This results in a tetragonal distortion of c/a = 1.052 ± 0.003, which is significantly higher than reported for epitaxial NiZAF films before [3][4][5].…”

“…The material is insulating and ferromagnetic at room temperature with low magnetic damping. Therefore, it can be considered as a good candidate [3][4][5] among few other materials, e.g. MAFO [6,7], all-perovskite oxides [8] and Fe alloyed with V and Al [9] as replacement, for the well known magnetic insulator yttrium iron garnet (YIG) [10,11].…”

“…In addition, the exact amount of Al in these PLD grown films was not reported. The Zn deficiency could be completely removed and even turned into an excess of Zn in NiZAF thin films grown by reactive magnetron sputtering (RMS) [4], resulting in an even higher strained material with slightly increased magnetic damping. Therefore, a systematic variation of the Zn content, and in a second step, the Al content should be performed in order to optimise the composition with regard to the desired soft magnetic properties of RMS grown thin films of NiZAF.…”