BaM Layer Research Articles

Dependence of the Structural and Magnetic Properties on the Growth Sequence in Heterostructures Designed by YbFeO3 and BaFe12O19.

The structure and the chemical composition of individual layers as well as of interfaces belonging to the two heterostructures M1 (BaFe12O19/YbFeO3/YSZ) and M2 (YbFeO3/BaFe12O19/YSZ) grown by pulsed laser deposition on yttria-stabilized zirconia (YSZ) substrates are deeply characterized by using a combination of methods such as high-resolution X-ray diffraction, transmission electron microscopy (TEM), and atomic-resolution scanning TEM with energy-dispersive X-ray spectroscopy. The temperature-dependent magnetic properties demonstrate two distinct heterostructures with different coercivity, anisotropy fields, and first anisotropy constants, which are related to the defect concentrations within the individual layers and to the degree of intermixing at the interface. The heterostructure with the stacking order BaFe12O19/YbFeO3, i.e., M1, exhibits a distinctive interface without any chemical intermixture, while an Fe-rich crystalline phase is observed in M2 both in atomic-resolution EDX maps and in mass density profiles. Additionally, M1 shows high c-axis orientation, which induces a higher anisotropy constant K1 as well as a larger coercivity due to a high number of phase boundaries. Despite the existence of a canted antiferromagnetic/ferromagnetic combination (T < 140 K), both heterostructures M1 and M2 do not reveal any detectable exchange bias at T = 50 K. Additionally, compressive residual strain on the BaM layer is found to be suppressing the ferromagnetism, thus reducing the Curie temperature (Tc) in the case of M1. These findings suggest that M1 (BaFe12O19/YbFeO3/YSZ) is suitable for magnetic storage applications.

Effect of Underlayer Quality on Microstructure, Stoichiometry, and Magnetic Properties of Hexaferrite BaFe12O19 Grown on YSZ(111) by Pulsed Laser Deposition.

We have studied the effect of platinum underlayer for two deposited thicknesses on the microstructure, crystalline quality, morphology, chemical composition, and magnetic properties as well as magnetic domain formation of BaFe12O19 (BaM) grown on YSZ(111) by pulsed laser deposition (PLD). We found that PLD platinum deposited with a thickness of 25 nm cannot withstand the dewetting phenomenon occurring during the subsequent BaM layer growth. A smooth and continuous Pt underlayer that possesses a sharp interface and omits the intermixing between the BaM and substrate was successfully achieved for a deposited Pt film thickness of 75 nm. Independent of the thickness of the deposited Pt layer, the c-axis orientation as well as coercivity Hc and the anisotropy HA fields were significantly improved due to a remarkable improvement of lattice mismatch in comparison with the BaM layer grown without a Pt underlayer on YSZ(111). By applying high-resolution X-ray diffraction, scanning and transmission electron microscopy (SEM/TEM), and atomically resolved scanning TEM imaging combined with energy-dispersive X-ray spectroscopy, as well as atomic and magnetic force microscopy, a comprehensive investigation of both structure and chemical composition of the deposited BaM films and their interfacial regions was performed. This study aimed to correlate the enhancement of the overall magnetic properties and of the local spin magnetic domain orientation with the modification of BaM microstructure and chemical composition at the nanometer scale due to the Pt underlayer. Finally, we attempted to understand the mechanisms that control the magnetic properties of these BaM films in order to be able to tailor them.

Optical Analysis Using Effective Medium Theory and Finite Element Method to Study the Enhanced Light Absorption in Porous BaMgAl10O17:Eu2+ Phosphor

The main objective of this paper is to reveal the mechanism of enhanced excitation light absorption in nano-pores structure BaMgAl10O17:Eu2+ (BAM) phosphor by optical analysis. The optical refractive index of the BAM was calculated from the reflectance spectra by Kramers–Kronig dispersion relation. And based on the effective medium theory, the anisotropic optical properties of porous BAM layer and its relations of absorption enhancement with porosity and thickness were investigated. A finite element simulation model was used for study the influence of pores size on optical properties. All the numerically evaluated results were match the experimental data.

Optical analysis using effective medium theory and finite element method to study the enhanced light absorption in porous BaMgAl-=SUB=-10-=/SUB=-O-=SUB=-17-=/SUB=- : Eu-=SUP=-2+-=/SUP=- phosphor

AbstractThe main objective of this paper is to reveal the mechanism of enhanced excitation light absorption in nano-pores structure BaMgAl_10O_17:Eu^2+ (BAM) phosphor by optical analysis. The optical refractive index of the BAM was calculated from the reflectance spectra by Kramers–Kronig dispersion relation. And based on the effective medium theory, the anisotropic optical properties of porous BAM layer and its relations of absorption enhancement with porosity and thickness were investigated. A finite element simulation model was used for study the influence of pores size on optical properties. All the numerically evaluated results were match the experimental data.

Thin films sputtered from Ba2NdFeNb4O15 multiferroic targets on BaFe12O19 coated substrates

Ba2NdFeNb4O15 tetragonal tungsten bronze (TTB)/BaFe12O19 (BaM) hexaferrite bilayers have been grown by RF magnetron sputtering on Pt/TiO2/SiO2/Si (PtS) substrates. The BaM layer is textured along (001) while the TTB layer is multioriented regardless of the PtS or BaM/PtS substrate. Dielectric properties of TTB films are similar to those of bulk, i.e., ε∼150 and a magnetic hysteresis loop is obtained from TTB/BaM bilayers, thanks to the BaM component. This demonstrates the possibility of transferring to 2 dimensional structures the composite multiferroic system TTB/BaM previously identified in 3 dimensional bulk ceramics.

Properties of Ba-Hexaferrite Thin Films with Different Layer Structures

M-type Ba-hexaferrite (BaM) thin films with two different structures (single layered and double layered) were deposited on (001) Al2O3 substrates by RF magnetron sputtering. The changes in microstructural and magnetic properties of the films corresponding to different layer structures and substrate temperatures (Ts) were investigated. Experimental results indicated that for the single layered films deposited directly on substrates at Ts = 300 °C and Ts = 500 °C, most of the grains are acicular type grains with their c-axis in-plane and/or randomly oriented. However, in the double layered film with first interfacial layer deposited at Ts = 300 °C and second layer deposited at Ts = 500 °C, good crystallographic characteristics and excellent perpendicular c-axis orientation were obtained. The c-axis dispersion angle (Δθc) decreased to 0.49°, while the squareness ratio and coercivity of the out-of-plane respectively increased to 0.85 and 4.67 kOe in the double layered film. The mechanism for improving perpendicular c-axis orientation with the interfacial BaM layer was attributed to an increase in the perpendicularly oriented nucleation sites and the release of the stress that comes from the film-substrate interface.

System Dynamics Modeling of Nitrogen Removal in a Stormwater Infiltration Basin with Biosorption‐Activated Media

Stormwater infiltration basins, one of the typical stormwater best management practices, are commonly constructed for surface water pollution control, flood mitigation, and groundwater restoration in rural or residential areas. These basins have soils with better infiltration capacity than the native soil; however, the ever-increasing contribution of nutrients to groundwater from stormwater due to urban expansion makes existing infiltration basins unable to meet groundwater quality criteria related to environmental sustainability and public health. This issue requires retrofitting current infiltration basins for flood control as well as nutrient control before the stormwater enters the groundwater. An existing stormwater infiltration basin in north-central Florida was selected, retrofitted, and monitored to identify subsurface physiochemical and biological processes during 2007-2010 to investigate nutrient control processes. This implementation in the nexus of contaminant hydrology and ecological engineering adopted amended soil layers packed with biosorption activated media (BAM; tire crumb, silt, clay, and sand) to perform nutrient removal in a partitioned forebay using a berm. This study presents an infiltration basin-nitrogen removal (IBNR) model, a system dynamics model that simulates nitrogen cycling in this BAM-based stormwater infiltration basin with respect to changing hydrologic conditions and varying dissolved nitrogen concentrations. Modeling outputs of IBNR indicate that denitrification is the biogeochemical indicator in the BAM layer that accounted for a loss of about one third of the total dissolved nitrogen mass input.

Effects of BaM Interfacial Layer on the $c$-Axis Orientation of BaM Thin Films Deposited on SiO$_{2}$/Si Substrates

M-type barium ferrite (BaM) thin films with two different structures (single layered and double layered) were deposited on thermally oxidized silicon (SiO2/Si) substrates by radio frequency (RF) magnetron sputtering. The changes in surface morphologies, crystallographic and magnetic properties of the films corresponding to different structures and substrate temperatures (Ts) were investigated in detail. In the single layered films deposited directly on SiO2/Si substrates at Ts = 300°C and Ts = 500°C respectively, most of the grains are acicular type. XRD data and magnetic properties measurement confirmed that they are both weakly c-axis perpendicularly oriented. However, in the double layered film with first interfacial layer deposited at Ts = 300°C and second layer deposited at Ts = 500°C, good crystallographic characteristics and excellent perpendicular c-axis orientation were obtained. The c-axis dispersion angle (Δθc) decreased to 0.51°C; the lattice parameters were comparable to those of the bulk BaM; the squareness ratio and coercivity of the out-of-plane increased to 0.85 and 338 kA/m, respectively, for the double layered film. The mechanism for improving perpendicular -axis orientation with an interfacial BaM layer was attributed to two reasons. One is a relative increase in the nucleation sites for perpendicularly oriented grains over the nucleation sites for in-plane and/or randomly oriented grains, and the other is the release of stress that comes from the interface between BaM thin film and SiO2/Si substrate.

Deposition of perpendicular c-axis oriented BaM thin films on (001) Al2O3 substrates by introducing an interfacial BaM buffer layer

M-type barium ferrite (BaM) thin films with two different structures (single layered and double layered) were deposited on (001) Al2O3 single crystal substrates using an RF magnetron sputtering system. The changes in the surface morphologies, crystallographic and magnetic properties of BaM thin films corresponding to the different structures and substrate temperatures (Ts) were investigated in detail. The results indicated that the interfacial BaM buffer layer plays an important role in improving the crystallographic and magnetic properties of BaM thin films. The single layered BaM thin films deposited at Ts=300°C and Ts=500°C are both randomly c-axis oriented. Whereas, by introducing a thin BaM layer which acts as an interfacial buffer layer, an excellent perpendicular c-axis orientation with an epitaxial structure for the double layered BaM thin film was obtained. The c-axis dispersion angle (Δθc) decreased to 0.49°, and the perpendicular squareness ratio increased to 0.85 for the double layered film. The mechanism for improving the perpendicular c-axis orientation with an interfacial BaM buffer layer was attributed to two reasons. One is a relative increase in the nucleation sites for perpendicularly oriented grains over the nucleation sites for in-plane and/or randomly oriented grains, and the other is the release of the stress that comes from the interface between BaM thin film and Al2O3 substrate.

Electric-field control of ferromagnetic resonance in monolithic BaFe12O19–Ba0.5Sr0.5TiO3 heterostructures

This paper demonstrates an electric-field tuning of the ferromagnetic resonance (FMR) responses at millimeter wave frequencies for a monolithic magneto-electric heterostructure. The layered stack is comprised of c-axis oriented and low loss barium hexaferrite (BaM) and (111) oriented ferroelectric barium strontium titanate (BSTO) layers along with embedded platinum electrode layers, all fabricated by pulsed laser deposition technique. A tunability of the FMR frequency as large as 3.5 MHz/V has been observed at 60 GHz due to application of bias voltages in the range of several volts. The realization of such a large tunability relies on the quasi-lattice-to-lattice contact between the BaM and BSTO layers as well as the high quality of those layers.

Preparation and magnetic properties of hexagonal barium ferrite films using BaM nanoparticles

Barium ferrite (BaFe 12O 19—BaM) thick films have been synthesized using a spinning coating sol–gel process. The coating sol was formed from BaM powders dispersed in the BaM raw sol. XRD, SEM, EDX, vibrating sample magnetometer (VSM), and ac susceptometer, were employed to evaluate the structure, composition and magnetic properties of BaM thick films. The results indicated that a uniform and crack-free coating of BaM with ∼15 μm thickness can be produced with good deal of consistency. The perpendicular and in-plane coercivity had the same value of 5 kOe. The high coercivity is attributed to the magnetocrystalline anisotropy and grain size of the sintered BaM layer. Effective magnetic susceptibility in all measurements have linear variation with increasing dc field.

Multifunctional dual-tunable low loss ferrite-ferroelctric heterostructures for microwave devices

Oriented barium ferrite (BaM) and polycrystalline ferroelectric barium strontium titanate (BSTO) layered structures have been fabricated by pulsed laser deposition. The 0.5μm thick BaM layer has a saturation induction of 4kG, a uniaxial effective anisotropy field of 16kOe, and a relatively low ferromagnetic resonance linewidth of about 25Oe, values that are indicative of a high quality film. The dielectric constant of the 0.9μm thick BSTO layer drops by a factor of 2 for an applied voltage of 3V.

Growth and characterization of sputtered BSTO∕BaM multilayers

Multilayers of Ba0.5Sr0.5TiO3 (BSTO) and BaFe12O19 (BaM), with tunable permeability and permittivity are attractive systems for radio frequency and microwave applications. We have grown multilayers of BSTO and BaM using magnetron sputtering on Al2O3 substrates. Film growth conditions such as sputtering parameters were optimized to obtain high quality multilayers. X-ray diffraction established that both BSTO and BaM were formed and cross-sectional SEM studies showed sharp interfaces between BSTO and BaM layers. Magnetization showed a large coercivity (∼2000Oe) consistent with the hexaferrite component. The hysteresis loops also revealed the distinct influence of magnetocrystalline and shape anisotropies at different temperatures.

Microstructure and magnetism in barium strontium titanate (BSTO)–barium hexaferrite (BaM) multilayers

High quality multilayers of barium ferrite (BaM) and barium strontium titanate (BSTO) were grown in optimized conditions on thermally oxidized Si(1 0 0) and Al 2O 3 substrates using magnetron sputtering. As-grown films were amorphous and different annealing procedures were explored to stabilize crystalline phases. BSTO and BaM phases were identified using X-ray diffraction and cross-sectional scanning electron micrographs showed sharp interfaces between BSTO and BaM layers. Magnetic hysteresis loops obtained at various temperatures and field orientations showed a large coercivity (∼2500 Oe) consistent with the hard magnetic hexaferrite component. Hysteresis loops also revealed the distinct influence of magnetocrystalline and shape anisotropies at different temperature ranges.

Manipulation of crystal orientation and microstructure of barium ferrite thin film

Pt, Pd, and Pt–Pd alloy underlayers were used to deposit c-axis oriented barium ferrite (BaM) thin films by a facing target sputtering system. All of the BaM thin films grown on these three underlayers show c-axis orientation normal to the film plane. But the grain size of BaM layer is strongly manipulated by the underlayer grain size. It is found that Pt–Pd alloy underlayer is effective to achieve c-axis oriented barium ferrite films with small grain size.

C-axis oriented Ba–ferrite thin film with small grain for perpendicular magnetic recording

Hexagonal Ba–ferrite(BaM) thin films with amorphous AlO(a-AlO) under-layer were prepared by a facing targets sputtering system. The grain size of c-axis perpendicularly oriented BaM/a-AlO films is about 20 nm at the thickness of 20 nm for BaM layer. The perpendicular coercivity is about 3.5–4.3 kOe with BaM layer thickness in the range from 80 to 30 nm and 2.3 kOe for BaM layer thickness of 20 nm.The in-plane coercivity for BaM/a-AlO films was less than 0.1 kOe at the thickness ranging from 20 to 80 nm.

Ex situ annealing method for c-axis oriented barium ferrite thick films

A barium hexaferrite (BaFe12O19, magnetoplumbite structure, BaM) multilayered film, with a total thickness of 0.63 μm, was deposited on a Si substrate by stacking several 0.09 μm layers using a rf sputtering technique. Each 0.09 μm layer was ex situ annealed at 800 °C for 10 min prior to deposition of the succeeding layer. A vibrating sample/torque magnetometer was employed to characterize the magnetic properties of both the BaM multilayered and a single layered film of the same thickness. The 0.63 μm thick BaM multilayered and single layered films show a squareness (SQ=Mr/Ms at 7 kOe) of 0.81 and 0.62, respectively. An anisotropy field (HA) was found to be 17 kOe for the BaM multilayered film and 14.5 kOe for the single layered film. A stacking of BaM layers, with ex situ annealing between each layer, improves the c-axis orientation and anisotropy field as compared to a single layered film with the same thickness. This is attributed to limiting the number of nucleation sites for randomly oriented BaM crystallites existing in films thicker than 0.1 μm.

Properties of Ba-ferrite/AlN double layered films for perpendicular magnetic recording media

In this paper, research works on Ba-ferrite (BaM) thin films achieved during the last two decades have been introduced. Magnetic properties of BaM/AlN films were studied. Grain size of BaM layer with an AlN underlayer was suppressed to 50–80 nm. A non-magnetic layer was formed between BaM and AlN layers due to the diffusion of Al. The H C⊥ for BaM/AlN films with c-axis orientation was 4.9 kOe at T S of about 600°C.

Perpendicular magnetic recording media using hexagonal ferrite thin films deposited on Pt underlayers and interlayers

Ba ferrite (BaM) thin films with excellent c-axis orientation were deposited on Pt(1 1 1) underlayers using Facing Targets Sputtering system. BaM thin films with extremely low thickness, as thin as 8 nm, exhibited apparent c-axis orientation. Such thin BaM layers exhibited small grain size. BaM/Pt multilayered structure was also effective to introduce exchange interaction among BaM crystallites.

Barium and strontium ferrite perpendicular thin film media with a sendust soft magnetic underlayer

The possibility of using sendust (FeAlSi) as the soft magnetic underlayer for hexagonal barium ferrite (BaM) and strontium ferrite (SrM) was studied. Sendust films were found to retain their soft magnetic properties with a rapid thermal anneal (RTA) at 800 C for 60 s, which is necessary to crystallize the as-deposited amorphous BaM and SrM films. Several film structures with sendust films as the soft underlayer were studied and compared. Strong hcp (001) texture and bcc (110) texture were obtained on the BaM(SrM)/Pt/buffer/FeAlSi/Si multi-layer structure films, as indicated by the strong hcp (006), (008) and (0014) reflections for BaM(SrM) layer and bcc (110) reflection for the sendust underlayer from X-ray diffraction measurements.