Showing papers on "Coercivity published in 2023"

Thickness scaling down to 5 nm of ferroelectric ScAlN on CMOS compatible molybdenum grown by molecular beam epitaxy

Abstract: We report on the thickness scaling behavior of ferroelectric Sc0.3Al0.7N (ScAlN) films grown on Mo substrates by molecular beam epitaxy. Switchable ferroelectricity is confirmed in ScAlN films with thicknesses ranging from 100 to 5 nm. An increase in coercive field and a significant diminution of remnant polarization are found when the ferroelectric layer is scaled down to below 20 nm. Notably, a switching voltage of 2–3.8 V and saturated remnant polarization of ∼23 μC/cm2 are measured in 5 nm thick ScAlN. X-ray diffractions and transmission electron microscopy studies indicate that the increase in coercive field and diminishment in switchable polarization can be closely linked to the surface oxidation and strain state in ultrathin ScAlN films. This work sheds light on the fundamental thickness scaling fingerprints of ScAlN thin films and represents an important step for next-generation compact and power-efficient devices and applications based on nitride ferroelectrics.

Impact of different magnetic materials added to silver–magnetite nanoparticles on the structural, magnetic and antimicrobial properties

Abstract: Abstract Different magnetic materials of spinel copper and cobalt nanoferrites added to silver–magnetite nanoparticles were fabricated by a facile, low cost, and rapid auto-combustion method to form a nanocomposite. X-ray diffraction patterns and atomic force microscopy were studied for the investigated samples and confirmed their nanosize range. Adding cobalt nanoferrite to silver–magnetite (CoAF) yielded a more pronounced effect in the magnetic measurements than adding copper nanoferrite (CuAF). This result was attributed to the much higher coercivity H c and saturation magnetization M s (5.7-fold and 2.8-fold, respectively) of CoAF than CuAF; accordingly, the CoAF nanocomposite can be applied to a permanent magnet. Next, the operating frequencies of the nanocomposites were calculated from the magnetic measurements. The CoAF and CuAF nanocomposites were applicable in the microwave super-high-frequency C-band and the microwave super-high-frequency S-band, respectively. Both nanocomposites were ineffective against the tested fungi but showed strong antimicrobial activities against the tested Gram-positive and Gram-negative bacteria. Thus, CoAF and CuAF nanocomposites are potential antibacterial nanomaterials for biomedical applications.

Structural and Physical Comparison Between CS/PVP Blend and CS/PVP/Sr-Hexaferrite Nanocomposite Films

Abstract: Abstract CS/PVP blend embedded by Sr-hexaferrite nanoparticles as a novel composite material to improve the optical and magnetic properties of composite samples. This work aimed to study and compare the functional and physical properties of CS/PVP film after and before adding SrFe 12 O 19 with different weight percentages to form nanocomposite film with chemical formula CS/PVP/x Wt% SrFe 12 O 19 ; x = 1, 3, 5 and 7. SrFe 12 O 19 was prepared successfully by using citrate auto-combustion methods, then added to CS/PVP blend with different weight percentages. XRD shows the formation of Sr-hexaferrite in a single phase with an average crystallite size 44 nm. The semi-crystalline nature of CS/PVP film decreases with the addition of Sr-hexaferrite. FTIR displays the interaction between CS/PVP and SrFe 12 O 19 by changing the intensity and broadening the OH band. HRTEM images show that SrFe 12 O 19 has a rod structure and has average particle size ranging from 50 to 100 nm. The coercivity value increased by increasing the weight% of nanofiller as it increased from 421 Oe for SrFe 12 O 19 to 4502.6 and 4488.2 Oe for x = 3 wt% and 7 wt% for SrFe 12 O 19 . The transition between the top of the valance band and the bottom of the conduction band in CS/PVP/ x Wt % SrFe 12 O 19; x = 1, 3, 5, 7 system occurred through the indirect transition.

Hard ferrite magnetic insulators revealing giant coercivity and sub-terahertz natural ferromagnetic resonance at 5-300 K.

Abstract: The temperature behavior of the magnetic properties is crucial for the application of magnetic materials. Recently, giant room temperature coercivities (20-36 kOe) and sub-terahertz natural ferromagnetic resonance (NFMR) frequencies (160-250 GHz) were observed for single-domain M-type hexaferrites with high aluminum substitution. Herein, the temperature dependences of the magnetic properties and natural ferromagnetic resonance are studied at 5-300 K for single-domain Sr1-x/12Cax/12Fe12-xAlxO19 (x = 1.5-5.5) particles. It is shown that the samples maintain their magnetic hardness over the whole temperature range. The coercivity and NFMR frequencies have a maximum shifting to the low-temperature region with a rise in aluminum concentration. The highest coercivity of 42 kOe and the maximum NFMR frequency of 297 GHz are observed for x = 5.5 at 180 K.

Ferroelectric [HfO 2 /ZrO 2 ] Superlattices with Enhanced Polarization, Tailored Coercive Field, and Improved High Temperature Reliability

Abstract: Modern microelectronic systems and applications demand an every increasing amount of non-volatile memories that are fast, reliable, and consume little power. Memory concepts based on ferroelectric HfO2 like the ferroelectric field effect transistor (FeFET) and the ferroelectric random access memory (FeRAM) are promising to satisfy these requirements. As a consequence, continuing high attention is given to improve the ferroelectric properties and the reliability characteristics of the ferroelectric HfO2 films –- for instance by using different dopant elements, dopant concentrations, and film thicknesses. Superlattices (i.e., a periodic structure of two materials stacked upon each other) are a promising alternative approach. Herein, [HfO2/ZrO2] superlattices of various sublayer thicknesses and a constant total thickness of 10 nm are embedded into metal-ferroelectric-metal (MFM) capacitors and then electrically as well as structurally characterized with special focus on remanent polarization, coercive field, endurance, and high temperature reliability. Compared to a 10 nm (Hf,Zr)O2 solid solution reference film, the use of superlattice stacks significantly improves the above mentioned parameters. In addition, most of these parameters depend on the sublayer thickness, which allows, for instance, tailoring the coercive field of the whole device.

Effect of La3+and Ni2+ substitution on Sr1-xLaxFe12-yNiyO19 hexaferrite structural, magnetic, and dielectric properties

Abstract: Herein, Sol-gel auto combustion is used to successfully synthesize M−type La3+ and Ni2+ substituted strontium nano-hexaferrite, Sr1-xLaxFe12-yNiyO19 (where × = y = 0.0, 0.05, 0.1, 0.15, and 0.2), powders. The prepared materials are sintered at a temperature of 1200 °C for 2 h. Characterization techniques like XRD, FT-IR, FE-SEM, VSM, and LCR Meter Bridge are used to study the structural, morphological, magnetic, and dielectric properties at room temperature. The XRD analysis of samples confirmed the formation of a single-phase hexagonal structure with P63/mmc space group. The saturation magnetization values initially increased and then decreased after × = 0.15 with the increase in La3+ and Ni2+ ions content. The coercivity showed irregular variation with the increase in dopants concentration. The loss tangent and dielectric constant parameters were also obtained to investigate the dielectric nature of prepared samples.

Using Preisach Theory to Evaluate Chemical Remanent Magnetization and Its Behavior During Thellier‐Thellier‐Coe Paleointensity Experiments

Abstract: The behavior of grain-growth chemical remanent magnetizations (gCRM) are investigated for different coercivity and magnetostatic-interaction-field distributions and acquisition conditions using a thermally activated Preisach model for assemblages of interacting single-domain grains. A new growth-rate dependent equation was derived, from which it was found that gCRM intensity is over 10% more sensitive to growth rate than previously modeled. We compare the gCRM results to the behavior of thermoremanences (TRM). gCRMs are two times more sensitive to changes in coercivity distribution, whereas TRMs are four times more sensitive to changes in magnetostatic interactions. The Thellier-Thellier-Coe paleointensity protocol was simulated in Preisach space, and gCRMs were found to produce concave-up Arai plots with pTRM checks which plot to the left of the Arai plot and positive partial-TRM tail checks that increase with magnetostatic interactions. This often leads to the failure of selection criteria, but high-temperature segments can pass the criteria for weakly interacting gCRMs; these estimates can underestimate the field by up to 66%.

Preparation and magnetic properties of Co2-based Heusler alloy glass-coated microwires with high Curie temperature

Abstract: In this article, we studied the effect of annealing (600 °C for 1 h) and the applied magnetic field from 50 Oe to 20 kOe of Co2FeSi glass-coated microwires with ordered L21 structure prepared by Taylor–Ulitovsky technique on the magnetic behavior. The as-prepared and annealed samples show a ferromagnetic behavior at the range of measuring temperature (5 to 400 K) and magnetic field (50 Oe to 20 kOe). M–H loops of as prepared sample do not show a squared shape. Meanwhile, perfectly squared hysteresis loops have detected for the annealed sample. In addition, annealed sample shows high magnetization M/M5K ratio, coercivity, and anisotropy field, as-compared to the as-prepared one. The annealed sample shows considerable irreversibility when the magnetic behavior changes with temperature upon the applied magnetic field at 50 and 200 Oe. Such irreversibility does not found in the as-prepared sample measured at the same magnetic field due to mixed amorphous and crystalline structure. By increasing the external magnetic field higher than 200 Oe and up to 20 kOe a gradual changing in the magnetic behavior has been detected where the irreversibility disappeared at applying magnetic field about 1 kOe and the magnetic behavior is totally change by increasing the external magnetic field up to the maximum 20 kOe. The difference in the magnetic behavior of the annealed glass-coated Co2FeSi glass-coated microwires indicates the effect of internal stresses induced by the presence of the glass-coating and the annealing-induced recrystallization.

CoFe2O4@HaP as Magnetic Heterostructures for Sustainable Wastewater Treatment

Abstract: The aim of this study was to synthesize a CoFe2O4@HaP nanocomposite (HaP-Hydroxyapatite) through the coprecipitation method in aqueous solution, with the purpose of using it in adsorption processes for the removal of Congo Red dye from aqueous solutions. Fourier Transform Infrared Spectroscopy (FT-IR) was used to characterize the synthesized material, identifying absorption bands specific to the functional groups of cobalt ferrite (Fe-O and Co-O at 603 and 472 cm−1) and hydroxyapatite PO43− at 1035, 962, 603 and 565 cm−1. Powder X-ray diffraction confirmed the cubic spinel structure of cobalt ferrite (S.G Fd-3m) and the hexagonal structure of hydroxyapatite (S.G P63/m). The nanocomposite’s crystallite size was calculated to be 57.88 nm. Nitrogen adsorption/desorption isotherms and BET specific surface area measurements were used to monitor textural parameters, revealing an increase in specific BET surface area when cobalt ferrite nanoparticles (15 m2/g) were introduced into the hydroxyapatite heterostructure (34 m2/g). Magnetic properties were investigated by interpreting hysteresis curves in the ±10 kOe range, with the nanocomposite showing a saturation magnetization of 34.83 emu/g and a coercivity value of 0.03 kOe. The adsorption capacity of the CoFe2O4@HaP nanocomposite is up to 15.25 mg/g and the pseudo-second-order kinetic model (Type 1) fits the data with a high correlation coefficient of 0.9984, indicating that the chemical adsorption determines the rate-determining step of the process. The obtained nanocomposite is confirmed by the analyses, and the absorption measurements demonstrate that it can be utilized to degrade Congo Red dye.

Thickness-dependent magnetic properties in Pt/[Co/Ni] n multilayers with perpendicular magnetic anisotropy

Abstract: We systematically investigated the Ni and Co thickness-dependent perpendicular magnetic anisotropy (PMA) coefficient, magnetic domain structures, and magnetization dynamics of Pt(5 nm)/[Co(t Co)/Ni(t Ni)]5/Pt(1 nm) multilayers by combining the four standard magnetic characterization techniques. The magnetic-related hysteresis loops obtained from the field-dependent magnetization M and anomalous Hall resistivity (AHR) ρxy showed that the two serial multilayers with t Co = 0.2 nm and 0.3 nm have the optimum PMA coefficient K U as well as the highest coercivity H C at the Ni thickness t Ni = 0.6 nm. Additionally, the magnetic domain structures obtained by magneto-optic Kerr effect (MOKE) microscopy also significantly depend on the thickness and K U of the films. Furthermore, the thickness-dependent linewidth of ferromagnetic resonance is inversely proportional to K U and H C, indicating that inhomogeneous magnetic properties dominate the linewidth. However, the intrinsic Gilbert damping constant determined by a linear fitting of the frequency-dependent linewidth does not depend on the Ni thickness and K U. Our results could help promote the PMA [Co/Ni] multilayer applications in various spintronic and spin-orbitronic devices.

Temperature dependent magnetic properties of NixCo1-xFe2O4: Single- and multidomain particles

Abstract: In the present work, nanocrystalline NixCo1-xFe2O4 oxides with average crystallite size between 11 nm and 111 nm have been analyzed by Mössbauer spectroscopy, hysteresis loops, field cooled (FC) and zero field cooled (ZFC) magnetization measurements. A core-shell model has been proposed. Accordingly, the Mössbauer spectra evidence a ferrimagnetic core and a disordered shell (spin-glass), the latter increasing with Ni concentration. Hysteresis curves reveal the ferromagnetic nature of the investigated compounds and transformation from single-to multi-domain behaviour at a critical particle size dependent on Ni2+ ion concentration. The magnetic properties of finest powders (average crystallite size ∼ 11 nm) are the most sensitive to the Ni2+ ions content. A general increase in the coercive field, HC, with reducing temperature according to the modified Kneller's formula Hc(T) = Hc(0)[1-(T/TB)β where β = 0.45 occurs. A high saturation magnetization of about 90 emu/g and an increase in HC from about 0.3 kOe at 300 K to 7 kOe at 10 K have been observed for the sample Ni0.1Co0.9Fe2O4 (x = 0.1). Increasing magnetization and coercive field with reducing temperature are also explained within the core shell model. FC and ZFC data show strong dependence of the magnetic properties on crystallite size and concentration of Ni2+ ions.