Magnetoelectric properties of epitaxial Fe3O4 thin films on (011) PMN-PT piezosubstrates

We determine the magnetic and magnetotransport properties of 33 nm thick Fe3O4 films epitaxially deposited by rf-magnetron sputtering on unpoled (011) [PbMg1/3Nb2/3O3](0.68) - [PbTiO3](0.32) (PMN-PT) substrates. The magnetoresistance (MR), as well as the magnetization reversal, strongly depend on the in-plane crystallographic direction of the epitaxial (011) Fe3O4 film and strain. When the magnetic field is applied along [100], the magnetization loops are slanted and the sign of the longitudinal MR changes from positive to negative around the Verwey transition at 125 K on cooling. Along the [01 (1) over bar] direction, the loops are square shaped and the MR is negative above the switching field across the whole temperature range, just increasing in absolute value when cooling from 300 K to 150 K. The value of the MR is found to be strongly affected by poling the PMN-PT substrate, decreasing in the [100] direction and slightly increasing in the [01 (1) over bar] direction upon poling, which results in a strained film

Strain engineering in epitaxial La1−xSr1+xMnO4 thin films

We have synthesized epitaxial thin films of La1−xSr1+xMnO4 with x = 0.0 and x = 0.5 by pulsed laser deposition on NdGaO3 and LaSrAlO4 substrates with different lattice mismatch. X-ray analysis shows that these layered doped manganites can be grown fully strained allowing to tune the lattice degrees of freedom which otherwise are a function of chemical composition x. Since the crystal structure is strongly coupled to the magnetic, orbital, and charge degrees of freedom in the doped manganites, the demonstrated strain engineering is the base for an extrinsic control of, e.g., charge-orbital order

Possible evidence for a spin-state crossover in the Verwey state inFe3O4thin films

In epitaxial thin films of magnetite a large change in magnetization across the Verwey transition has been observed. In the Verwey state, the sample magnetization appeared to be strongly reduced, in some samples even close to zero. Using superconducting quantum interference magnetometry, x-ray absorption near edge spectroscopy, and polarized neutron reflectometry, a simple rotation of the magnetization vector due to a change in magnetocrystalline anisotropy was excluded. The experimental data rather suggest an intrinsic loss of magnetic moment due to a possible transition into a low or intermediate spin state of Fe2+. This observation discloses a different aspect of the Verwey transition

Intrinsic versus extrinsic ferromagnetism in HfO2−x and Ni:HfO2−x thin films

We have investigated the possible evolution of an intrinsic stable ferromagnetic moment in oxygen deficient undoped and magnetically doped HfO2−x thin films grown by reactive molecular beam epitaxy. Neither oxygen vacancies nor substituted Ni in combination with such vacancies results in an observable magnetic moment for a broad range of oxygen vacancy concentrations. By combining integral and element specific magnetization measurements, we show that a fluctuating deposition rate of the magnetic dopant induces extrinsic ferromagnetism by promoting the formation of metallic clusters. We suggest the element specific measurement of an induced magnetic moment at the nonmagnetic site as a proof of intrinsic ferromagnetism in diluted magnetic semiconductors

Nanoporous Silicon Oxycarbonitride Ceramics Derived from Polysilazanes In situ Modified with Nickel Nanoparticles

Ni–polysilazane precursors were synthesized from polysilazane and trans- [bis(2-aminoetanol-N,O)diacetato-nickel(II)]. The Ni–polysilazane precursors are superparamagnetic indicating formation of nanosized nickel particles (2−3 nm) confirmed by HRTEM as well. The as-obtained Ni–polysilazane precursors were thermolized at 700 °C and transformed to ceramic nanocomposites, manifesting a nanoporous structure, revealing a BET surface area of 215 m2 g–1, a micropore surface area of 205 m2 g–1, and a micropore volume of 0.113 cm3 g–1. Although Si–C–N–(O) ceramics derived from the native polysilazane are nonporous, the pronounced development of porosity in the Ni/Si–C–N–(O) system was attributed to (i) the stabilizing effect of carbosilane bonds, which prohibit the formation of macropores during thermolysis; (ii) the reduced barrier for heterogeneous pore nucleation as a result of in situ created nickel nanoparticles; and (iii) the reduced viscous flow of the pores due to the presence of nickel nanoparticles and turbostratic carbon. The formation of turbostratic carbon is due to the reactions catalyzed by nickel nanoparticles that result in graphene stacking as inferred from the STA–MS studies

High-temperature stability and saturation magnetization of superparamagnetic nickel nanoparticles in microporous polysilazane-derived ceramics and their gas permeation properties

Superparamagnetic Ni nanoparticles with diameters of about 3 nm are formed in situ at room temperature in a polysilazane matrix, forming Ni/polysilazane nanocomposite, in the reaction between a polysilazane and trans-bis(aceto-kO) bis(2-aminoethanol-k2N,O)nickel(II). The thermolysis of the Ni/polysilazane nanocomposite at 700 °C in an argon atmosphere results in a microporous superparamagnetic Ni/silicon oxycarbonitride (Ni/SiCNO) ceramic nanocomposite. The growth of Ni nanoparticles in Ni/SiCNO ceramic nanocomposite is totally suppressed even after thermolysis at 700 °C, as confirmed by HRTEM and SQUID characterizations. The analysis of saturation magnetization of Ni nanoparticles in Ni/polysilazane and Ni/SiCNO nanocomposites indicates that the saturation magnetization of Ni nanoparticles is higher than expected values and infers that the surfaces of Ni nanoparticles are not oxidized. The microporous superparamagnetic Ni/SiCNO nanocomposite is shaped as a free-standing monolith and foam. In addition, Ni/SiCNO membranes are fabricated by the dip-coating of a tubular alumina substrate in a dispersion of Ni/polysilazane in THF followed by a thermolysis at 700 °C under an argon atmosphere. The gas separation performance of Ni/SiCNO membranes at 25 and 300 °C is assessed by the single gas permeance (pressure rise technique) using He, H2, CO2, N2, CH4, n-propene, n-propane, n-butene, n-butane, and SF6 as probe molecules. After hydrothermal treatment, the higher increase in the hydrogen permeance compared to the permeance of other gases as a function of temperature indicates that the hydrogen affinity of Ni nanoparticles influences the transport of hydrogen in the Ni/SiCNO membrane and Ni nanoparticles stabilize the structure against hydrothermal corrosion

High-Temperature Stability and Saturation Magnetization of Superparamagnetic Nickel Nanoparticles in Microporous Polysilazane-Derived Ceramics and their Gas Permeation Properties

Superparamagnetic Ni nanoparticles with diameters of about 3 nm are formed in situ at room temperature in a polysilazane matrix, forming Ni/polysilazane nanocomposite, in the reaction between a polysilazane and <i>trans</i>-bis­(aceto-<i>k</i>O)­bis­(2-aminoethanol-<i>k</i>²N,O)­nickel­(II). The thermolysis of the Ni/polysilazane nanocomposite at 700 °C in an argon atmosphere results in a microporous superparamagnetic Ni/silicon oxycarbonitride (Ni/SiCNO) ceramic nanocomposite. The growth of Ni nanoparticles in Ni/SiCNO ceramic nanocomposite is totally suppressed even after thermolysis at 700 °C, as confirmed by HRTEM and SQUID characterizations. The analysis of saturation magnetization of Ni nanoparticles in Ni/polysilazane and Ni/SiCNO nanocomposites indicates that the saturation magnetization of Ni nanoparticles is higher than expected values and infers that the surfaces of Ni nanoparticles are not oxidized. The microporous superparamagnetic Ni/SiCNO nanocomposite is shaped as a free-standing monolith and foam. In addition, Ni/SiCNO membranes are fabricated by the dip-coating of a tubular alumina substrate in a dispersion of Ni/polysilazane in THF followed by a thermolysis at 700 °C under an argon atmosphere. The gas separation performance of Ni/SiCNO membranes at 25 and 300 °C is assessed by the single gas permeance (pressure rise technique) using He, H₂, CO₂, N₂, CH₄, n-propene, n-propane, n-butene, n-butane, and SF₆ as probe molecules. After hydrothermal treatment, the higher increase in the hydrogen permeance compared to the permeance of other gases as a function of temperature indicates that the hydrogen affinity of Ni nanoparticles influences the transport of hydrogen in the Ni/SiCNO membrane and Ni nanoparticles stabilize the structure against hydrothermal corrosion

High Mobility Indium Zinc Oxide Thin Film Field-Effect Transistors by Semiconductor Layer Engineering

Indium zinc oxide thin-film transistors are fabricated via a precursor in solution route on silicon substrates with silicon dioxide gate dielectric. It is found that the extracted mobility rises, peaks, and then decreases with increasing precursor concentration instead of rising and saturating. Investigation with scanning probe techniques reveals full thickness variations within the film which are assumed to adversely affect charge transport. Additional layers are coated, and the extracted mobility is observed to increase up to 19.7 cm2 V–1 s–1. The reasons for this are examined in detail by direct imaging with scanning tunneling microscopy and extracting electron density profiles from X-ray reflection measurements. It is found that the optimal concentration for single layer films is suboptimal when coating multiple layers and in fact using many layers of very low concentrations of precursor in the solution, leading to a dense, defect and void free film, affording the highest mobilities. A consistent qualitative model of layer formation is developed explaining how the morphology of the film develops as the concentration of precursor in the initial solution is varied