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Register a new userInfluence of structure and cation distribution on magnetic anisotropy and damping in Zn/Al doped nickel ferrites
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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$^{2+}_{text{Td}}$ and cation coordination of Fe$^{2+}_{text{Oh}}$ on the intrinsic damping is found. Furthermore, the critical role of the incorporation of Zn$^{2+}$ and Al$^{3+}$ is evidenced by comparison with a sample of altered composition. Especially, the dopant Zn$^{2+}$ is evidenced as a tuning factor for Ni$^{2+}_{text{Td}}$ and therefore unquenched orbital moments directly controlling the g-factor. A strain-independent reduction of the magnetic anisotropy and damping by adapting the cation distribution is demonstrated.
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The comparative study of the substitution of zinc and lithium for iron in the 114 ferrites, YBaFe4O7 and CaBaFe4O7, shows that these diamagnetic cations play a major role in tuning the competition between ferrimagnetism and magnetic frustration in these oxides. The substitution of Li or Zn for Fe in the cubic phase YBaFe4O7 leads to a structural transition to a hexagonal phase YBaFe4-xMxO7, for M = Li (0.30 < x < 0.75) and for M = Zn (0.40 < x < 1.50). It is seen that for low doping values i.e. x = 0.30 (for Li) and x = 0.40 (for Zn), these diamagnetic cations induce a strong ferrimagnetic component in the samples, in contrast to the spin glass behaviour of the cubic phase. In all the hexagonal phases, YBaFe4-xMxO7 and CaBaFe4-xMxO7 with M = Li and Zn, it is seen that in the low doping regime (x ~ 0.3 to 0.5), the competition between ferrimagnetism and 2 D magnetic frustration is dominated by the average valency of iron. In contrast, in the high doping regime (x ~ 1.5), the emergence of a spin glass is controlled by the high degree of cationic disorder, irrespective of the iron valency.
We have investigated the Vanadium- (V) substituted Ni-Zn-Co ferrites where the samples were prepared using solid-state reaction technique. The impact of V5+ substitution on the structural, magnetic, dielectric and electrical properties of Ni-Zn-Co ferrites has been studied. XRD analysis confirmed the formation of a single-phase cubic spinel structure. The lattice constants have been calculated both theoretically and experimentally along with other structural parameters such as bulk density, X-ray density and porosity. The FESEM images are taken to study the surface morphology. FTIR measurement is also performed which confirms spinel structure formation. The saturation magnetization (Ms), coercive field (Hc) and Bohr magneton (B) were calculated from the obtained M-H loops. The temperature dependent permeability is studied to obtain the Curie temperature. Frequency and composition dependence of permeability was also analyzed. Dielectric behavior and ac resistivity are also subjected to investigate the frequency dependency. An inverse relationship was observed between the composition dependence of dielectric constant and ac resistivity. The obtained results such as the electrical resistivity, dielectric constants and magnetic properties suggest the appropriateness of the studied ferrites in microwave device applications.
Ferromagnetic resonance (FMR) was used to investigate the static and dynamic magnetic properties of carbon-doped Mn5Ge3 (C$_{0.1}$ and C$_{0.2}$) thin films grown on Ge(111). The temperature dependence of magnetic anisotropy shows an increased perpendicular magneto-crystalline contribution at 80K with an in-plane easy axis due to the large shape contribution. We find that our samples show a small FMR linewidth (corresponding to an intrinsic magnetic damping parameter $alpha$=0.005), which is a measure of the spin relaxation and directly related with the magnetic and structural quality of the material. In the perpendicular-to-plane geometry, the FMR linewidth shows a minimum at around 200K for all the samples, which seems to be not correlated to the C-doping. The magnetic relaxation parameters have been determined and indicate the two-magnon scattering as the main extrinsic contribution. We observe a change in the main contribution from scattering centres in Mn5Ge3C0.2 at low temperatures, which could be related to the minimum in linewidth.
Thick-section plates made from a recently developed Al-Cu-Mg-Li alloy have been evaluated to understand the influence of microstructure on the anisotropy of tensile strengths after natural and artificial ageing treatment. Pancake-shaped grains with a coarse substructure and strong crystallographic texture with a beta-fibre orientation at the mid-thickness position are observed. In addition, an inhomogeneous distribution of T1 precipitates through the plate thickness has been revealed with the volume fraction of intragranular precipitates ~ 40% higher at the plate centre than the thickness position. Altogether these microstructural features contribute to the in-plane anisotropy of tensile strengths that is ~ 5% higher at the mid-thickness position than the 1/4 thickness position. The variation of ageing-induced T1 precipitates through the plate thickness further contributes to the through-thickness anisotropy that is ~ 3% higher in T8 temper as compared to T3 temper.
The Mg-Zn and Al-Zn binary alloys have been investigated theoretically under static isotropic pressure. The stable phases of these binaries on both initially hexagonal-close-packed (HCP) and face-centered-cubic (FCC) lattices have been determined by utilizing an iterative approach that uses a configurational cluster expansion method, Monte Carlo search algorithm, and density functional theory (DFT) calculations. Based on 64-atom models, it is shown that the most stable phases of the Mg-Zn binary alloy under ambient condition are $rm MgZn_3$, $rm Mg_{19}Zn_{45}$, $rm MgZn$, and $rm Mg_{34}Zn_{30}$ for the HCP, and $rm MgZn_3$ and $rm MgZn$ for the FCC lattice, whereas the Al-Zn binary is energetically unfavorable throughout the entire composition range for both the HCP and FCC lattices under all conditions. By applying an isotropic pressure in the HCP lattice, $rm Mg_{19}Zn_{45}$ turns into an unstable phase at P$approx$$10$~GPa, a new stable phase $rm Mg_{3}Zn$ appears at P$gtrsim$$20$~GPa, and $rm Mg_{34}Zn_{30}$ becomes unstable for P$gtrsim$$30$~GPa. For FCC lattice, the $rm Mg_{3}Zn$ phase weakly touches the convex hull at P$gtrsim$$20$~GPa while the other stable phases remain intact up to $approx$$120$~GPa. Furthermore, making use of the obtained DFT results, bulk modulus has been computed for several compositions up to pressure values of the order of $approx$$120$~GPa. The findings suggest that one can switch between $rm Mg$-rich and $rm Zn$-rich early-stage clusters simply by applying external pressure. $rm Zn$-rich alloys and precipitates are more favorable in terms of stiffness and stability against external deformation.
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