Vacancy filled nickel‐cobalt‐titanate thin films

et al. 2019

Annalen der Physik

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Insulating uniaxial room-temperature ferromagnets are a prerequisite for commonplace spin wave-based devices, the obstacle in contemporary ferromagnets being the coupling of ferromagnetism with large conductivity. It is shown that the uniaxial A 1 + 2x Ti 4+ 1 − x O 3 (ATO), A = Ni 2+ ,Co 2+ , and 0.6 < x ≤ 1, thin films are electrically insulating ferromagnets already at room temperature. The octahedra network of the ATO and the corundum and ilmenite structures are the same yet different octahedra-filling proved to be a route to switch from the antiferromagnetic to ferromagnetic regime. Octahedra can continuously be filled up to x = 1, or vacated (−0.24 < x < 0) in the ATO structure. TiO-layers, which separate the ferromagnetic (Ni,Co)O-layers and intermediate the antiferromagnetic coupling between the ferromagnetic layers in the NiTiO 3 and CoTiO 3 ilmenites, can continuously be replaced by (Ni,Co)O-layers to convert the ATO-films to ferromagnetic insulator with abundant direct cation interactions.

Section: Resultsmentioning

confidence: 61%

11 \bar{2} 0

) substrate, the film exhibited preferred 00 l orientation . Shape anisotropy favors magnetization M in the plane of the film and often has a large effect on the direction of M .…”

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

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Room‐Temperature Insulating Ferromagnetic (Ni,Co)₁₊₂_xTi₁₋_xO₃ Thin Films

Fujioka¹,

Frantti²,

et al. 2019

Annalen der Physik

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Simulation of the Impact of Point Defects and Edge Dislocations on X‐Ray Diffraction in Hexagonal (Ni,Co)_1+2xTi_1−xO₃ Thin Films

Frantti¹,

Fujioka²,

Physica Status Solidi (b)

et al. 2022

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Understanding and controlling crystal defects are essential in material engineering, the classical example being semiconductor devices created by a spatially well-controlled point defect distribution. [1] 2D defects include domain wall and grain boundaries. Polarization reversal in ferroelectric materials is essentially dictated by domain walls, whose dynamics can be highly complex. [2] The meaning of domains and domain boundaries for the polarization reversal in ferroelectrics is as crucial as the role of dislocations for the plasticity of metals. [3] Edge dislocations are classified as line defects which are frequently formed in strained thin films. In case the lattice mismatch exceeds the critical value, edge dislocations are formed. After exceeding the critical thickness, the lattice parameters relax to their natural values. A spatially extended displacement field accompanies dislocation, which in diffraction measurements is often seen as an asymmetric line shape. Determination of the strain and dislocation density are key parameters in semiconductor devices based on the epitaxial thin films.Crystal defects have a decisive role for the properties of thin films, yet their nondestructive structural characterization is challenging as the volume is characteristically small and the films are grown on a substrate. X-ray diffraction (XRD) is the prevailing route for nondestructively characterizing crystals and their defects. [4][5][6][7] XRD analysis relies on results extracted from bulk samples, single crystals, and powders. XRD data collected on thin-film samples possessing several layers are commonly considered to be consisting of noninteracting layers, the result being a sum of the patterns from each layer (or phase). To estimate the phase fractions, standard profile functions (e.g., Lorentz, Pearson or pseudo-Voigt) are commonly applied to model reflection intensities. The approach suits for the polycrystalline materials lacking features resulting from long-range order (e.g., subsidiary peaks in thin films) but is an overly coarse approach for highly ordered nanoscale structures. For instance, while asymmetric line shapes can routinely be fit by the standard line profiles, it is often hard to ascertain the origin of the asymmetry.In this article, another approach is taken to model defected films. The films, with spatially varying composition and structure, are taken as a single scattering unit. As the dimensions are small, between 10 and 100 nm, the scattered X-ray intensity profile is to an excellent accuracy determined by the sample, and no preassumed profile function is applied. We first simulate diffraction patterns from the homogeneous (Ni 0.42 Co 0.58 ) 2.22 Ti 0.39 O 3 film possessing atomic-scale disorder and second from hexagonal (Ni,Co) 3 O 3 thin films under compressive biaxial strain and edge dislocations. The situation contrasts to the case where no stress relaxation by dislocation has taken place. Thus, the simulations suit for cases where the standard measurements in which d-spacing for a chosen ...

Permanently Magnetized Insulating Thin‐Film Devices by Reduction

Frantti¹,

Fujioka²,

Physica Rapid Research Ltrs

et al. 2020

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A reduction‐based manufacturing process for creating technologically important multilayer structures from lattice‐matched ferromagnetic insulators and ferromagnetic conductors is reported. The process is demonstrated by growing a permanently magnetized double‐layer structure, consisting of lattice‐matched conducting (Ni,Co) and insulating (Ni0.4Co0.6)3O3 layers, through a single deposition cycle. The orientation of the metal cation network is preserved after reduction. Close‐packing displacements of Ni and Co take place in such a manner that the in‐plane hexagonal arrangement is preserved. This is critical for ensuring high‐quality interfaces joining the layers. At room temperature the hysteresis loop is centered. At low temperature the oxide layer becomes ferrimagnetically ordered, accompanied by a shift of the hysteresis loop along the magnetic field axis. The shift is assigned to exchange bias phenomenon. Biaxial compressive strain is responsible for the required ferrimagnetic ordering. Spin valves and closely related magnetoresistance random access memory and spin‐transfer‐torque magnetic random access memory devices are addressed as potential applications.