Room Temperature Ferromagnetic Properties Research Articles

Structural and room temperature ferromagnetic properties of Fe3+-Doped CuCrO2 fibers

Undoped CuCrO2 and Fe-doped CuCrO2 fibers at 3, 5 and 10 at.% were synthesized using an electrospinning method and calcined at 865 °C for 7 h under a vacuum. X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) methodology and vibrating sample magnetometry (VSM) were used to analyze the synthesized samples. Characterization from XRD patterns indicated a single phase delaffosite-type CuCrO2 in all samples. Lattice parameters, a and c, increased to 2.987 Å and 17.122 Å, respectively, at a 10 at.% level of Fe3+ dopant compared to that of undoped CuCrO2 where a was 2.974 Å and c was 17.094 Å. SEM and TEM results confirmed the morphology of CuCrO2 fibers with an average diameter in the range of 0.67 ± 0.20 to 1.85 ± 0.57 μm. Specific surface areas of all synthesized fibers were investigated using BET methodology. With magnetic characterization obtained from VSM results, undoped CuCrO2 showed ferromagnetic (FM) behavior at room temperature (RT) with a magnetization (M) value of 0.0016 emu/g. All samples of Fe-doped CuCrO2 fibers displayed RT-FM behavior, with higher M values than that of undoped CuCrO2, 0.0224 emu/g at 10 at.% Fe. Indirect superexchange and double-exchange mechanisms are discussed in this work. The novelty of this work on the prepared fibers is the observation of a single phase of CuCrO2 in undoped and Fe-doped CuCrO2 fibers with a high dopant concentration of 10 at.% and showing RT-FM for all prepared Fe-doped CuCrO2 fibers.

The effect of composition on the structure, optical, and room-temperature ferromagnetic properties of hydrothermally synthesized (ZnSn)1-xCuxO nanocomposites

(ZnSn)1-xCuxO nanocomposites (NCs) with nanorods and nanosheet morphologies were synthesized by a facile hydrothermal technique. (ZnSn)1-xCuxO NCs exhibited a gradual band gap redshift from UV to visible spectral region with increasing Cu-content. The room temperature magnetic hysteresis loop indicated the improvement of room temperature ferromagnetic (RTFM) behavior of (ZnSn)1-xCuxO NCs compared with nanostructured ZnSnO NCs induced by the exchange interaction of Cu-bound polarons with the localized spins and free carriers. The (ZnSn)60Cu40O NCs exhibited the highest saturation magnetization (Ms) of 0.539 emu·g−1. Further increase in Cu-content resulted in the deterioration of crystalline domains and the reduction of Ms to 0.259 emu·g−1. This behavior revealed that the electronic and magnetic properties of (ZnSn)1-xCuxO NCs were so sensitive to the dopant concentration that need to be utilized for improving their performance as good candidate NCs for spintronic applications.

Tunable room-temperature ferromagnetism in RF magnetron sputtered Al2Cr2Cu2O8 thin film

Metal oxide solid solution thin films containing ternary mixtures of Alumina (Al2O3), Chromia (Cr2O3) and Cupric oxide (CuO) were successfully prepared combinatorially on FTO, quartz glass and Si substrates using radio frequency (RF) magnetron sputtering (vertical geometry; on-axis sputtering) technique with RF powers of 200 W and 100 W. XRD analysis prove the development of tetragonal phase Al2Cr2Cu2O8 in sputtering target. Al2Cr2Cu2O8 film deposited on Si wafer and quartz glass exhibits amorphous nature, whereas, the film deposited on FTO substrates exhibit crystalline structure with tetragonal phase owing to polycrystalline nature of the FTO substrates. Formation of high compositional purity with acceptable stoichiometric ratio of ternary metal oxide mixtures of Al2Cr2Cu2O8 was ascertained from the EDX spectra. The thicknesses of Al2Cr2Cu2O8 thin films are found to be in the ranges from 259 to 314 nm. Optical study showed that the optical energy band gap of Al2Cr2Cu2O8 thin film deposited on quartz substrates increased to 3.84 eV from 3.78 eV with decreasing RF power from 200 W to 100 W. The spin orbital splitting (SOS) between Cr 2p1/2 - Cr 2p3/2 and Cu 2p1/2 - Cu 2p3/2 were measured to be 9.9 eV and 19.3 eV by XPS for 200 W sputtered Al2Cr2Cu2O8 film on quartz substrate, which are the characteristics of Cr3+ and Cu2+ oxidation states, respectively. In addition, XPS analysis also confirms the presence of various oxygen vacancies in Al2Cr2Cu2O8 thin films (as-deposited and 1000 °C annealed films) on quartz substrate with RF power of 200 W, which is the most favorable condition for the presence of room temperature ferromagnetic properties observed in the present study.

Doping Dy improves magnetism and electricity in hexagonal boron nitride

Dy-doped hexagonal boron nitride with a circular flaky structure and a diameter of 50 nm was prepared through high-temperature reduction reactions. The hexagonal boron nitride nanosheets (hBNNSs) exhibit both room-temperature ferromagnetism and semiconductor conductivity properties. Doping with Dy transforms hBNNSs from insulators to magnetic semiconductors. The saturation magnetization of hBNNSs with a Dy doping content of 0.58 at.% at room temperature is 0.1405 emu/g. This suggests that the Curie temperature of Dy-doped hBNNSs is above room temperature. With increasing temperature, the current of the hBN film rises, demonstrating semiconductor conductive behavior. First-principles calculations indicate that the magnetic properties of the material primarily arise from the f-orbital electrons of the Dy element, while the electrical properties are mainly attributed to the Fermi energy level crossing of the conduction band, influenced by the f-orbital and d-orbital electrons of the Dy element.

Defects mediated weak ferromagnetism in Zn1−yCyO (0.00 ≤ y ≤ 0.10) nanorods semiconductors for spintronics applications

A series of carbon-doped ZnO [Zn1−yCyO (0.00 ≤ y ≤ 0.10)] nanorods were synthesized using a cost-effective low-temperature (85 °C) dip coating technique. X-ray diffractometer scans of the samples revealed the hexagonal structure of the C-doped ZnO samples, except for y = 0.10. XRD analysis confirmed a decrease in the unit cell volume after doping C into the ZnO matrix, likely due to the incorporation of carbon at oxygen sites (CO defects) resulting from ionic size differences. The morphological analysis confirmed the presence of hexagonal-shaped nanorods. X-ray photoelectron spectroscopy identified C–Zn–C bonding, i.e., CO defects, Zn–O–C bond formation, O–C–O bonding, oxygen vacancies, and sp2-bonded carbon in the C-doped ZnO structure with different compositions. We analyzed the deconvoluted PL visible broadband emission through fitted Gaussian peaks to estimate various defects for electron transition within the bandgap. Raman spectroscopy confirmed the vibrational modes of each constituent. We observed a stronger room-temperature ferromagnetic nature in the y = 0.02 composition with a magnetization of 0.0018 emu/cc, corresponding to the highest CO defects concentration and the lowest measured bandgap (3.00 eV) compared to other samples. Partial density of states analysis demonstrated that magnetism from carbon is dominant due to its p-orbitals. We anticipate that if carbon substitutes oxygen sites in the ZnO structure, the C-2p orbitals become localized and create two holes at each site, leading to enhanced p–p type interactions and strong spin interactions between carbon atoms and carriers. This phenomenon can stabilize the long-range order of room-temperature ferromagnetism properties for spintronic applications.

Correlation of oxygen defects, oxide-ion conductivity and dielectric relaxation to electronic structure and room temperature ferromagnetic properties of Yb3+ doped CeO2 nanoparticles

Ce1-xYbxO2 nanoparticles synthesized using co-precipitation route were studied for properties like structural, optical, impedance and X-ray Photoelectron Spectroscopy. Existence of cubic fluorite structure found intact with heterogeneous aggregation and spherical surface morphology. Red-shifted energy gap along with formation of defects and oxygen vacancies was confirmed with UV–Vis and Photoluminescence analyses. XPS analyses were undertaken to observe the chemical states 2+ and 3+ of Yb and 3+ and 4+ of Ce cations. The magnetization results demonstrated improved ferromagnetic ordering for varying Yb doping, explained with Bound Magnetic Polarons model and F-Centre Mechanism for creation of distinct complexes, Ce4+-Vo-Ce3+ or Yb3+-Vo-Ce3+ in the CeO2 lattice. All samples' dielectric permittivity and modulus were measured in the 120 Hz–100 kHz frequency range. The ∈′ (f) and ∈″(f) plots show two distinct regions: a plateau zone at high frequency and low frequency dielectric dispersion region. These nanoparticles could be employed for photolytic, optoelectronics and energy storage applications.

Green-synthesized Nickel oxide nanoparticles: Magnetic and biomedical applications

In this work, cubic Nickel oxide (NiO) nanoparticles (NPs) were prepared by a hotplate combustion process using Calotropis gigantea (crown flower) leaf extract as fuel. The synthesized NPs were characterized by analytical techniques like Powder X-ray diffraction (PXRD), UV–visible spectroscopy (UV–vis), Transmission electron microscope (TEM), Scanning electron microscope (SEM), and Vibrating sample magnetometer (VSM). PXRD results confirmed the formation of single-phase crystalline NiO NPs with an average crystallite size of 17.06 nm. Further, SEM and TEM analysis shows the formation of hexagonal-shaped NiO NPs with agglomeration. The energy bandgap of 3.04 eV was observed for the NiO NPs by optical studies. The vibrational stretching mode of Ni-O (431 cm−1) was validated by FTIR analysis. VSM studies reveal room temperature ferromagnetic property. The as-prepared NPs were subjected to a cytotoxicity test against liver cancer (HepG2) cell line using an MTT assay and significant anticancer activity was observed. Furthermore, an antibacterial assay indicates gram-negative bacteria is more defiant of antibiotic drugs than gram-positive bacteria.

Effective role of vibrational annealing in enhancing room temperature physical properties of Co doped ZnO nanoparticles by using novel TVA technique

Well-annealed nanocrystalline semiconductor materials in pellet or thin film form, composed of small grains with a high surface-to-volume ratio, are considered as promising candidates for multiple device applications. However, no such method is available yet that can control the grain size of such samples during heat treatment. In this present work, a novel thermo-vibrational annealing (TVA) setup for processing nanocrystalline materials was designed and fabricated in-house. Here both thermal and mechanical vibrational energy were simultaneously applied to the sample during annealing, followed by vibrational dry quenching in the presence of an inert gas environment. Co-doped ZnO pellets were synthesized by chemical route pyrophoric method followed by annealing at 800 °C for 4 h using this set up. For comparison, one pellet was annealed with vibration with calibrated vibration at a speed of 360 rpm, and another pellet was annealed without vibration. X-ray diffraction (XRD), Raman and Fourier transform Infrared (FTIR) spectroscopic studies showed the formation of a single crystalline phase with hexagonal wurtzite structure of both the samples and the proper incorporation of Co2+ ions into the ZnO matrix without any impurity phases, which was also confirmed by energy dispersive X-ray (EDX) spectroscopy studies. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) studies confirmed the decrease in average grain and particle size of the sample when processed with the TVA setup. Ultraviolet–Visible spectra showed that the bandgap energy of the Co-doped ZnO sample varies inversely with particle size. Hall-effect measurements demonstrated the semiconducting nature of both samples with n-type charge carriers. The presence of Co2+ ions in the wurtzite ZnO lattice was confirmed by X-ray photoelectron spectroscopy (XPS). The magnetic properties were studied using a SQUID magnetometer, which confirmed that a Co doped ZnO sample annealed with the TVA technique exhibit better room temperature ferromagnetism properties compared to sample annealed without vibration. Based on these studies, it was believed that the sample annealed by mechanical vibrational energy with vibrational dry quenching has a great influence on several physical properties of any material and hence Co doped ZnO sample processed with this TVA technique can be used as a promising candidate for multiple sensor and magnetic storage devices.

One-Step, In Situ Hydrothermal Fabrication of Cobalt-Doped ZnO/CdS Nanosheets for Optoelectronic Applications

An in-situ hydrothermal process was used to create Co-doped ZnO/CdS nanosheets in order to examine the effects of the divalent impurity (Co) ions on the structural, morphological, optical, and magnetic characteristics of the test material. For both ZnO and CdS, XRD verified the development of a hexagonal wurtzite structure. SEM, TEM, and HR-TEM studies produced sheet-like morphology. Elemental mapping and XPS examination verified the presence of essential elements (S, Cd, O, Co, and Zn). Co-doping dramatically increased the nanosheets’ ability to absorb light in the visible area. Comparing the bandgap energy to pure ZnO and ZnO/CdS nanocomposites, the bandgap energy (2.59 eV) was well-regulated. The PL spectrum at 577 nm showed a prominent yellow emission band that was attributed to the 4A2g(F) → 4T1g(F) transition. Improvement in the room temperature ferromagnetic properties was observed due to doping of Co2+ ions. Warm white light harvesting was confirmed by the estimated CCT value (3540 K). The test material appears to be suitable for the creation of next-generation optoelectronic devices.

Two-dimensional Janus SVAN2 (A = Si, Ge) monolayers with intrinsic semiconductor character and room temperature ferromagnetism: tunable electronic properties via strain and an electric field.

In the context of developing next-generation information technology, two-dimensional materials with inherent ferromagnetism, a Curie temperature above room temperature, and significant magnetic anisotropy hold great promise. In this work, we employed first-principles calculations to investigate a novel two-dimensional Janus structure, namely SVAN2 (A = Si, Ge). Our findings reveal that these structures are not only dynamically and thermally stable, but also exhibit semiconductor properties alongside their ferromagnetic states. The Janus SVSiN2 monolayer exhibits an in-plane easy axis, while the SVGeN2 monolayer shows an out-of-plane easy axis, both characterized by a significant magnetic anisotropy energy (129 and 172 μeV, respectively). Notably, through Monte Carlo simulation, we found that the Curie temperature of the SVSiN2 monolayer is 330 K, which is higher than room temperature. Finally, by applying biaxial strain and an external electric field, we successfully regulated the electronic properties of the SVAN2 (A = Si, Ge) monolayers, enabling a transition from semiconductor to half-metallic behavior. These remarkable electronic and magnetic properties make the Janus SVAN2 (A = Si, Ge) monolayers promising candidate materials for spin electron applications.

The optimal tuning of electronic structure, magnetic, and optical properties of (Fe, V + VO/VSn) co-doped SnO2 via first-principles calculations.

Dilute magnetic semiconductors (DMSs) with both charge and spin degrees of freedom have emerged as promising candidates in the spintronic industry. However, the Curie temperature below room temperature and uncertainty about the origin of ferromagnetism hinder the application of DMSs. To address these issues, we explored a better SnO2-based co-doped method (Fe, V + VSn) using ab initio calculations. The calculation results show that the Sn13FeVO32 (Fe, V + VSn) has a high Curie temperature (716K), good ferromagnetic properties, stronger covalency of bonds, and better optical transparency in the visible light range. In addition, the holes or electrons generated by the complexes in the (Fe, V + VO/VSn) co-doped system cause a spin-polarized double exchange effect in the Fe-3d, V-3d, and O-2p orbitals, which leads to magnetism of the co-doped systems. The static dielectric constant ɛ1(0) of the system increases after doping. Among them, Sn14FeVO31 (Fe, V + VO) has the largest ɛ1(0), indicating that Sn14FeVO31 has the strongest polarization ability and better photocatalytic properties. In Sn14FeVO31, the imaginary part of the dielectric function and the absorption spectrum all have new peaks in the low-energy region, which are caused by the jump of electrons from the guide band of the spin-polarized impurity energy level. This paper proposes a new method for preparing dilute magnetic semiconductors in spin electronic devices with high room temperature ferromagnetic properties and excellent optical properties through the (Fe, V + VO/VSn) co-doped SnO2.

Composition-Controllable Syntheses and Property Modulations from 2D Ferromagnetic Fe5 Se8 to Metallic Fe3 Se4 Nanosheets.

Exploring new-type 2D magnetic materials with high magnetic transition temperature and robust air stability has attracted wide attention for developing innovative spintronic devices. Recently, intercalation of native metal atoms into the van der Waals gaps of 2D layered transition metal dichalcogenides (TMDs) has been developed to form 2D non-layered magnetic TMDs, while only succeeded in limited systems (e.g., Cr2 S3 , Cr5 Te8 ). Herein, composition-controllable syntheses of 2D non-layered iron selenide nanosheets (25% Fe-intercalated triclinic Fe5 Se8 and 50% Fe-intercalated monoclinic Fe3 Se4 ) are firstly reported, via a robust chemical vapor deposition strategy. Specifically, the 2D Fe5 Se8 exhibits intrinsic room-temperature ferromagnetic property, which is explained by the change of electron spin states from layered 1T'-FeSe2 to non-layered Fe-intercalated Fe5 Se8 based on density functional theory calculations. In contrast, the ultrathin Fe3 Se4 presents novel metallic features comparable with that of metallic TMDs. This work hereby sheds light on the composition-controllable synthesis and fundamental property exploration of 2D self-intercalation induced novel TMDs compounds, by propelling their application explorations in nanoelectronics and spintronics-related fields.

Alternating Magnetic Field Induced Magnetic Heating in Ferromagnetic Cobalt Single-Atom Catalysts for Efficient Oxygen Evolution Reaction.

Alternating magnetic field (AMF) is a promising methodology for further improving magnetic single-atom catalyst (SAC) activity toward oxygen evolution reaction (OER). Herein, the anchoring of Co single atoms on MoS2 support (Co@MoS2), leading to the appearance of in-plane room-temperature ferromagnetic properties, is favorable for the parallel spin arrangement of oxygen atoms when a magnetic field is applied. Moreover, field-assisted electrocatalytic experiments confirmed that the spin direction of Co@MoS2 is changing with the applied magnetic field. On this basis, under AMF, the active sites in ferromagnetic Co@MoS2 were heated by exploiting the magnetic heating generated from spin polarization flip of these SACs to further expedite OER efficiency, with overpotential at 10 mA cm-2 reduced from 317 mV to 250 mV. This work introduces a feasible and efficient approach to enhance the OER performance of Co@MoS2 by AMF, shedding some light on the further development of magnetic SACs for energy conversion.

Plasma assists titanium nitride and surface modified titanium nitride nanoparticles from titanium scraps for magnetic properties and supercapacitor applications

Plasma methods are efficient processing for metal recovery from metal scrap, bearing minerals, electronic waste, etc. In this work, pure titanium nitride nanoparticles (TiN NPs) were synthesized from titanium scraps by the thermal plasma arc discharge (TPAD) method. TPAD synthesized TiN NPs have a highly crystalline nature with cubic and spherical morphologies with average particle sizes of 30–100 nm. Further, prepared TiN NPs involving surface modification (SM) or etching processes were investigated by using the non-thermal DC glow discharge plasma technique with air atmosphere at different processing times. SM@TiN NPs have a comparatively low crystalline, which was confirmed from the powder X-ray diffraction technique. SM@TiN NPs have very interesting core shell morphologies, which are due to the surface interactions of ionized air molecules. TiN and SM@TiN NPs have room-temperature ferromagnetic properties with high saturation magnetization (Ms) up to 2.6 and 3.0 emu/g and very high coercivity (Hc) of 235.5 Oe, respectively. TiN and SM@TiN NPs have superior energy storage performance with an outstanding specific capacitance of 192.8 and 435.1 F/g at a current density of 2 A/g with pseudocapacitive behavior. These results reveal that TiN and SM@TiN NPs have highly promising electrodes for supercapacitor applications.

Mono, dual and tri-doped TiO2: Sunlight photocatalytic, room temperature ferromagnetic and dielectric constant properties

In this study, the optical, magnetic and electrical properties of nanostructured TiO2 semiconductor have been investigated for multi-functional applications. Herein, different compositions composed of TiO2, Ti0.985Co0.015O2, Ti0.97Co0.015Mn0.015O2, Ti0.97Co0.015Fe0.015O2 and Ti0.97Co0.01Mn0.01Fe0.01O2 were synthesized by coprecipitation method. The XRD and Rietveld refinement analysis confirmed that TiO2, Ti0.985Co0.015O2, Ti0.97Co0.015Mn0.015O2 and Ti0.97Co0.01Mn0.01Fe0.01O2 powders have mixed phases of rutile and anatase TiO2 structure while Ti0.97Co0.015Fe0.015O2 powder has anatase structure. The incorporation of Co, (Co, Mn), (Co, Fe) and (Co, Mn, Fe) ions into TiO2 lattice decreases the band gap energy from 3.13 eV to 3.05, 2.7, 3.08 and 2.88 eV, respectively. Ti0.985Co0.015O2 and Ti0.97Co0.015Fe0.015O2 samples exhibit high sunlight efficiencies of 73% and 72% for Congo red (CR) dye degradation in 80 min, respectively. The dielectric constant and electrical conductivity of TiO2 were enhanced due to insertion of Co2+, Mn2+ and Fe2+/3+ ions. Among all samples, Ti0.97Co0.015Mn0.015O2 composition reveals the highest dielectric constant value of 5004. On the other hand, notable room temperature ferromagnetism with found in Ti0.97Co0.015Fe0.015O2 composition with magnetization value of 0.056 emu/g and coercivity of 86 Oe. The obtained results confirmed that the incorporation of Co2+, Mn2+ and Fe2+/3+ ions into TiO2 enhances the electrical, magnetic and photocatalytic properties.

Large room-temperature ferromagnetism in ordered porous In2O3 films

In this paper, ordered porous In2O3 films were prepared on ordered porous Al2O3 thin films by magnetron sputtering. The film shows large room-temperature ferromagnetism of 18.78 emu/cm3, and the saturation magnetization is more than ten times larger than in the dense In2O3 film. Moreover, the magnetic anisotropy of the ordered porous In2O3 film was observed, and the saturation magnetization in the direction perpendicular to the film surface is much greater than in the direction parallel to the film surface. In addition, by investigating the room-temperature ferromagnetism and photoluminescence properties of the film under different environments, the room-temperature ferromagnetism of ordered porous In2O3 films is most affected by the oxygen vacancies. The research in this paper provides a solid basis for the development of spintronic devices.

Oxygen vacancies and defects induced room temperature ferromagnetic properties of pure and Fe-doped CeO2 nanomaterials investigated using X-ray photoelectron spectroscopy

Structural, Optical, Magnetic and Electronic-state properties of co-precipitation method synthesized pure CeO2 and Ce1−xFexO2 nanomaterials have been analysed in pursuit of room temperature ferromagnetism and creation cum storage of oxygen vacancies for technological applications. Intact cubic fluorite structure after doping with presence of defects and oxygen vacancies are confirmed by XRD and Raman analysis. The grain size distribution of all the nanomaterials in 4–5 nm range is discussed with TEM images. Core level XPS spectra of Ce-3d, Fe-2p and O-1s are discussed to account for the change in valence state of cerium ion from Ce4+ to Ce3+. Oxygen vacancies generated due to substitution of Ce4+ by Fe3+ ion at Ce ion sites are responsible for observed weak ferromagnetism. The results for weak ferromagnetism in pure CeO2 and Ce1−xFexO2 samples are explained by correlating the F-center exchange mechanism with the formation of F+ center complexes Fe3+(↑)−VO(↓)−Ce3+(↑) and Ce3+↑−VO↓−Ce4+(↑) enjoined by oxygen vacancies.

Unveiling Semiconductor Nanostructured Based Holmium-Doped ZnO: Structural, Luminescent and Room Temperature Ferromagnetic Properties.

This research work describes the synthesis of ZnO nanostructures doped with Ho3+ ions using a conventional sol–gel synthesis method. The nanostructured produced exhibited a wurtzite hexagonal structure in both ZnO and ZnO:Ho3+ (0.25, 0.5, 0.75 mol%) samples. The change in morphology with addition of Ho3+ dopants was observed, which was assigned to Ostwald ripening effect occurring during the nanoparticles’ growth. The photoluminescence emission properties of the doped samples revealed that Ho3+ was emitting through its electronic transitions. Moreover, reduced surface defects were observed in the Holmium doped samples whose analysis was undertaken using an X-ray Photoelectron Spectroscopy (XPS) technique. Finally, enhanced room temperature ferromagnetism (RT-FM) for Ho3+-doped ZnO (0.5 mol%) samples with a peak-to-peak line width of 452 G was detected and found to be highly correlated to the UV–VIS transmittance results.

Theoretical and experimental study of (Ga1-xFex)2O3 ternary alloys

Thin films of Ga2O3 and its alloys open the possibility of ultrawide bandgap heterostructure device designs that includes HEMT, quantum well UV optoelectronics, wide bandgap spintronics, high resistive buffer layers for FET and electrocatalytic applications. In this paper, (Ga1-xFex)2O3 (for x = 0.0–0.50) thin film alloys as a function of growth temperatures (450–750 °C) and partial oxygen pressures (10-1 −10-6 torr) grown using pulsed laser deposition are reported. The results suggest that, with the increase of Fe content at a fixed growth temperature and pressure, the bandgap decreases (4.93 to 3.43 eV and 4.39 to 2.25 eV for direct and indirect, respectively) due to a change in the Fe oxidation states as the Fe composition is increased from 0 to 50%. Density functional theory calculations also show a reduction in the bandgap of the alloy as the Fe content increases with the formation of a localized band of states close to the conduction band. Fe content, ≥ 40% in the alloy leads a phase change in the crystal structure with the formation of a gamma phase, also corroborated by theoretical calculations. Finally, room temperature ferromagnetic property was observed in thin films with the introduction of Fe into the Ga2O3 lattice.

Interface-driven static and dynamic magnetic properties of ultrathin Fe/Ge multilayers

Ferromagnet-semiconductor (FM-SC) alloy phase with room temperature ferromagnetic properties at the interfaces of FM/SC heterostructures are believed to improve the electron spin injection from the FM to the SC for the realization of spintronic devices. Here we report the formation of a crystalline alloy phase (Fe3Ge) at the interfaces on growing ultrathin Fe/Ge multilayers at an elevated substrate temperature of ∼ 523 K as well as on annealing the multilayer at a temperature > 523 K. The alloy phase formation at interfaces is achieved at a much lower temperature than the Fe3Ge phase formation in bulk material (∼973 K), mainly due to rapid interdiffusion of Fe and Ge at the interfaces which is about 4 (∼2) order higher in magnitude than the diffusion of Ge (Fe) in the bulk crystalline phase. We find a large magnetic anisotropy constant (K ∼ 3 × 106 to 7 × 107 erg/cm3) on the formation of the nanocrystalline alloy phase at interfaces. Ultrathin Fe/Ge multilayers were characterized using x-ray scattering, macroscopic magnetization measurement, and polarized neutron reflectivity (PNR). The temperature-induced diffusion process indicates that the alloy phase is structurally stable up to higher temperature. PNR provided a detailed depth profile of the magnetization in the system and suggested that the alloy phase is ferromagnetic at room temperature. We have also studied the dynamic magnetic properties of these systems by employing ferromagnetic resonance measurements.