High Saturation Magnetic Moment Research Articles

Above-room-temperature strong intrinsic ferromagnetism in 2D van der Waals Fe3GaTe2 with large perpendicular magnetic anisotropy

The absence of two-dimensional (2D) van der Waals (vdW) ferromagnetic crystals with both above-room-temperature strong intrinsic ferromagnetism and large perpendicular magnetic anisotropy (PMA) severely hinders practical applications of 2D vdW crystals in next-generation low-power magnetoelectronic and spintronic devices. Here, we report a vdW intrinsic ferromagnetic crystal Fe3GaTe2 that exhibits record-high above-room-temperature Curie temperature (Tc, ~350-380 K) for known 2D vdW intrinsic ferromagnets, high saturation magnetic moment (40.11 emu/g), large PMA energy density (~4.79 × 105 J/m3), and large anomalous Hall angle (3%) at room temperature. Such large room-temperature PMA is better than conventional widely-used ferromagnetic films like CoFeB, and one order of magnitude larger than known 2D vdW intrinsic ferromagnets. Room-temperature thickness and angle-dependent anomalous Hall devices and direct magnetic domains imaging based on Fe3GaTe2 nanosheet have been realized. This work provides an avenue for room-temperature 2D ferromagnetism, electrical control of 2D ferromagnetism and promote the practical applications of 2D-vdW-integrated spintronic devices.

Electrospun, Oriented, Ferromagnetic Ni 1-x Fe x Nanofibers.

Electrospinning has been used to fabricate ferromagnetic Ni0.47Fe0.53 nanofiber mats that were composed of individual, orientated Ni0.47Fe0.53 nanofibers. The key steps were processing a polyvinylpyrrolidone nanofiber template containing ferric nitrate and nickel acetate metal precursors in Ar at 300°C and then 95% Ar: 5% H2 at 600°C. The Ni0.47Fe0.53 fibers were nanostructured and contained Ni0.47Fe0.53 nanocrystals with average diameters of ~14 nm. The Ni0.47Fe0.53 ferromagnetic mats had a high saturation magnetic moment per formula unit that was comparable to those reported in other studies of nanostructured Ni1-xFex. There is a small spin-disordered fraction that is typically seen in nanoscale ferromagnets and is likely to be caused by the surface of the nanofibers. There was an additional magnetic contribution that could possibly stem from a small Fe1-zNizO phase fraction surrounding the fibers. The coercivity was found to be enhanced when compared with the bulk material.

Fe doping-stabilized γ-Ga2O3thin films with a high room temperature saturation magnetic moment

A thermostable Fe-doped γ-Ga2O3thin film with a high room temperature saturation magnetic moment of 5.73μB/Fe has been obtained for the first time.

Mixed Phase Crystalline Hausmannite and Manganese Ferrite Nanoparticles with Magnetic Properties for Environmental Application

High surface to volume ratio in ferrites results novel phenomena of nanomagnetism such as superparamagnetism, magnetic quantum tunneling and spin-glasslike behavior, attracting the science community. MnFe2O4 is one of such important magnetic oxides with tunable magnetic properties and Mn3O4 is the most stable form of manganese oxide with paramagnetic behavior. The composite of these two outstanding materials of is synthesized by a simple chemical precipitation method using NaOH as the precipitating agent. Ferric chloride anhydrous (FeCl3) and manganese chloride tetra hydrate (MnCl2.4H2O) were used as iron and manganese sources respectively. The samples were annealed at 400°C for eight hours to obtain homogeneous powder of Manganese ferrite. The powders were characterized by using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and Fourier transform infrared spectroscopic (FTIR) measurements. The sample was found polycrystalline on X-ray diffraction study. The magnetic properties of the sample were investigated by vibrating sample magnetometer (VSM) measurements. From the magnetic moment vs. magnetic field plot, the sample was found to have high saturation magnetic moment of 30.12 emu/g. The synthesized nano-composite was used as adsorbent for removal toxic dye reactive orange (RO) from water and its easy magnetic serration process is explored. In addition to environmental application, this nano-composite with such an appreciable magnetic moment along with its electrical properties will be a candidate material for different applications in electronics and exploring its functionality in the field of recently developing semiconductor device physics and spintronics.

Large reversible magnetocaloric effect induced by metamagnetic transition in antiferromagnetic HoNiGa compound**Project supported by the National Natural Science Foundation of China (Grant Nos. 51671022 and 51427806), the Beijing Natural Science Foundation, China (Grant No. 2162022), and the Fundamental Research Funds for the Central Universities, China (Grant No. FRF-TP-15-002A3).

The magnetic properties and magnetocaloric effects (MCE) of HoNiGa compound are investigated systematically. The HoNiGa exhibits a weak antiferromagnetic (AFM) ground state below the Ńeel temperature TN of 10 K, and the AFM ordering could be converted into ferromagnetic (FM) ordering by external magnetic field. Moreover, the field-induced FM phase exhibits a high saturation magnetic moment and a large change of magnetization around the transition temperature, which then result in a large MCE. A large −ΔSM of 22.0 J/kg K and a high RC value of 279 J/kg without magnetic hysteresis are obtained for a magnetic field change of 5 T, which are comparable to or even larger than those of some other magnetic refrigerant materials in the same temperature range. Besides, the μ0H2/3 dependence of well follows the linear fitting according to the mean-field approximation, suggesting the nature of second-order FM–PM magnetic transition under high magnetic fields. The large reversible MCE induced by metamagnetic transition suggests that HoNiGa compound could be a promising material for magnetic refrigeration in low temperature range.

Synthesis and characterization of dilute magnetic semiconductor based on Zn1−xMnxO thin films prepared by 5-methyl-7-methoxyisoflavone modified sol-gel/spin-coating technique

Zn1−xMnxO2 (0.01≤x≤0.09) thin films were prepared by 5-methyl-7-methoxyisoflavone modified sol-gel/spin-coating technique on Quartz substrates to improve their optical properties and room temperature ferromagnetism for spintronic applications. The crystal structure, chemical composition, magnetic and optical properties of these films were investigated by X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, vibrating magnetometer and spectrophotometry. The incorporation of Mn ions into the hexagonal crystal structure of ZnO gave rise to an increase of the unit cell volume and a decrease of the crystal residual stress. However, the introduction of the Mn2+ ions into the ZnO nanocrystals lead to a decrease of the band energy gap from 3.23eV to 2.63eV. The films showed an average optical transparency of 88%. The XPS spectra revealed that 80% of the incorporated Mn ions into the ZnO crystal structure are in the form of Mn2+ and 20% in the form of Mn4+. The replacement of Zn+2 ions by Mn2+ ions resulted in an increase of the amount of the surface oxygen vacancy. The magnetization was improved by more than 50 times compared conventional methods. Therefore, remarkable room temperature ferromagnetism with high saturation magnetic moment (3.32μB/Mn) and high coercivity (280G) were obtained.

Searching for magnetism in pyrrolic N-doped graphene synthesized via hydrothermal reaction

Improving the ferromagnetism property of graphene materials is particularly important for a wide range of applications such as spintronics, magnetic memory, and other electromagnetic devices. Pyrrolic nitrogen (N) doping is an effective means to enhance the ferromagnetism of graphene materials. Here we report the synthesis of N-doped graphene with 6.02at.% doping concentration through a high-throughput hydrothermal method. X-ray photoelectron spectroscopy reveals that the pyrrolic N bonding configuration dominates over the other bonding types observed in our samples, which is in good agreement with the Raman spectroscopy and first-principle calculations. The vibrating sample magnetometer and SQUID are employed to further analyze the magnetic properties of the pyrrolic N-doped graphene. At room temperature, the sample exhibits significant ferromagnetism with a high saturation magnetic moment (1.4×10−2emu/g) among graphene materials and a narrow coercivity (181.4Oe). Our results have not only extended the synthesis method of N-doped graphene materials but also deepened the fundamental understanding of the N doping behaviors in enhancing their magnetism.

Structure and magnetic properties of diluted magnetic metal oxides based on Cu-doped CeO2 nanopowders

The development of engineered nanostructures with precise morphology has gained significant attention due to new properties of these materials. Herein, we report a novel recipe to synthesize Ce1−xCuxO nanostructures via a hexamethylene triperoxide diamine assisted solvothermal method. The influence of Cu ion concentration (0.01≤x≤0.10) on the structure and morphology of the CeO nanocrystals was examined. The X-ray photoelectron spectroscopy demonstrated that the copper atoms tend to be incorporated into the CeO crystal structure in the form of Cu2+. At the Cu ion concentration x=0.09, the Cu-doped CeO2 displayed a very high saturation magnetic moment of 1.58μB/Co and coercivity of 154 G. The synthetic method designed in this work enhanced the ferromagnetic properties of the Ce1−xCuxO nanostructures compared to the materials obtained by conventional techniques.

Iron Oxide Nanoparticles Prepared by Modified Co-Precipitation Method

The safe, targeted and effective release of drugs for therapeutics from nanostructured functional materials, particularly nanoparticles (NPs), has attracted much attention due to the ability to diagnose and cure of cancer and other ailments. The potential of magnetic NPs, that stems from intrinsic properties of their magnetic cores combined with their drug, can be exploited for clinical applications. Two main magnetic requirements for bionanotechnology-a high saturation magnetic moment and a near-zero remanence-occur in superparamagnetic materials. Here, we report synthesis of magnetite NPs by modified coprecipitation method. The effect of pH on the shape and size of NPs has also been reported in this paper. For superparamagnetic nature, the size of the NPs has great significance and should be compatible with the living cell. Ferric and ferrous chlorides are used as precursors and the amount of NaOH was varied to control the size and shape of the nanoparticles. X-ray diffraction patterns show the formation of magnetites. Scanning electron microscopy reveals that the prepared nanoparticles have size compatible with the diseased cell. M-H curves show the superparamagnetic nature of the nanoparticles, hence these NPs are well suited for the magnetic resonance imaging as the contrast agents, for cell tagging, magnetic separation, and hyperthermia treatments.

Role of hydroxyl (OH) on structural and ferrimagnetism of annealed CoFe2O4 nanoparticles

Cobalt ferrites (CoFe2O4) with high magnetic moments and coercivity are proposed for the fabrication of media recording devices; however, their very high coercivity, which produces noise, is big hurdle in the practical form of these devices. Cobalt ferrites with high magnetic moment and moderate coercivity, and the role of hydroxyls on the structural and ferrimagnetic properties, have been investigated in detail. The proposed research investigates the following aspects that are important in understanding the role of hydroxyls: (1) the average particle size and presence of hydroxyls are correlated to the annealing temperatures, and (2) the hydroxyls have considerably influenced the structure and magnetic ordering in the nanocrystal. The prepared single spinel structure of cobalt ferrites exhibits good saturated hysteresis loops with ferrimagnetic behaviour and annealing at high temperature observed to play a significant role for the tuning of particle size, saturation magnetisation, coercivity and remnant magnetisation. The removal of hydroxyl at high temperatures in CoFe2O4 shows a stable crystallinity with high saturation magnetic moment and moderate coercivity. The novel aspect of the proposed system is the presence of hydroxyls at low annealing temperature, and later, the removal of these hydroxyls at high annealing temperature plays an important role for modifying the magnetic properties. The application of the research can be imagined as applications of media recording devices with low noise and high efficiency and also as antimicrobial/medical applications in biomaterials.

Magnetism regulation of (In1−x Fe x )2O3 semiconductors prepared by sol-gel method

Fe doped In2O3 samples (In1−xFex)2O3 (x=0, 0.05, 0.1, 0.2 and 0.3) on glass substrate were prepared by sol-gel method. The XRD results demonstrate that the solubility of Fe ions in In2O3 matrix is around 20%, above which impurity phase can be observed. The transmittance of the samples with x=0, 0.05, 0.1 and 0.2 are above 80% in the visible region while the transimittance of the glass is 90%. The transmittance curves slightly red-shifts as x increasing. All of the samples except x=0 are ferromagnetic at room temperature. The highest saturation magnetization moment is reached in the sample x=0.2 with 330 emu/cm3, and the coercive force is 169 Oe which is also the largest in our samples. The results indicate that the addition of Fe ions could tune the structure, the ferromagnetism and optical property in the In2O3 matrix.

Design and fabrication of non-superparamagnetic high moment magnetic nanoparticles for bioapplications

We present a new type of magnetic nanoparticles for bioapplications. Multilayered nanodisks consisting of two magnetic layers separated by a non-magnetic layer with two capping layers were designed and fabricated. Two key magnetic requirements for bioapplications, a high saturation magnetic moment and a near-zero remanence, were achieved through the magnetostatic interlayer coupling between two magnetic layers. Capping layers provide functionalization sites for biomolecule attachment. A pillar-template-based synthesis method was employed for fabrication. Nanodisks with a diameter of 70 nm and a thickness of 60 nm were produced in large quantity. The magnetic characterization shows that each nanodisk possesses a magnetic moment equivalent to 100 10-nm Co nanoparticles and a near-zero remanent moment.

Room Temperature Ferromagnetism of Mn Implanted AlInN

Ferromagnetic properties of Mn-implanted wurtzite AlxIn1-xN/GaN thin films grown by metal organic chemical vapor deposition (MOCVD) were observed using a quantum design superconducting quantum interference device (SQUID) magnetometer. Hysteresis behavior with a reasonably high saturation magnetic moment at room temperature for all the samples was noted. Two optical thresholds were observed at 1.58 and 2.64 eV, which are attributed to internal transition (5E→5T2) of Mn3+ (d4) and hole emission from the neutral Mn acceptor level to the valence band respectively. Bound magnetic polaron formation is considered to be the origin of ferromagnetism in our samples.

Electron stabilized ferromagnetism in GaGdN

AbstractWith the aim of understanding the observed roomtemperature giant magnetic moment of highly diluted GaGdN reported in literature GaGdN, GaGdN:Si and GaGdN:H have been grown by molecular beam epitaxy (MBE) and the Gd concentration is between 1016 and 1021 cm3. All samples are ferromagnetic at 300 K as measured by SQUID and the very high saturation magnetic moment in this type of samples is confirmed by our experiments.With co‐doping of hydrogen or silicon we were able to decrease or increase the strength of the magnetic moments in the layers, respectively. All our findings indicate that ferromagnetism is stabilized by electrons. Electrical measurements on GaGdN layers grown on highly resistive 6H‐SiC (0001) show a typical temperature dependence of hopping conductivity. The resistivity of the material is 0,1 to 13 kΩ cm in the temperature range from 60 to 10 K. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Room-temperature ferromagnetism in Mn and Fe codoped In2O3

The synthesis and characterization of polycrystalline room-temperature ferromagnetic semiconductor (In0.9Fe0.1−xMnx)2O3 (x=0–0.1) oxide are reported. All of the samples with intermediate x values are ferromagnetic at room temperature. The highest saturation magnetization moment at 300K per total amount of magnetic ion is reached in the (In0.9Fe0.04Mn0.06)2O3 sample. The lattice constant a increases linearly with increasing Mn content. Fe-only doped samples were paramagnetic, while a Mn-only doped sample was found to be ferromagnetic below TC=46K.

Magnetic structure of Nd 7Co 6Al 7

Time-of-flight neutron powder diffraction has been used to determine the magnetic structure of the intermetallic compound Nd 7Co 6Al 7. The thermodynamic, magnetic and electrical properties of this compound indicate that it undergoes a paramagnetic–ferromagnetic transition at 15.5 K, and possesses a magnetic refrigerant capacity of approximately 40 J/kg. The average value of the high field saturation magnetic moment per Nd atom at low temperatures is almost 50% below that of the free ion value. Neutron powder diffraction measurements have been performed at 300 K, in order to confirm the details of the crystal structure, and below the magnetic ordering temperature, at 6 K, in order to establish the nature of the magnetic structure. The high temperature data clearly confirm that Nd 7Co 6Al 7 crystallizes in the Pr 7Co 6Al 7 structure (space group P4/ mbm). The low temperature data show the presence of reflections at (100), (110), (200) and (210), reflections which are non-existent above the ordering temperature. The presence of the (100) reflection indicates the presence of antiferromagnetic configurations in this system. Models of the magnetic structure for Nd 7Co 6Al 7 will be presented and discussed.

Scalar Relativistic Spin Polarized Electronic Structure of Ferromagnetic fcc GdAl2

Typical magnetic Laves phase structure substances as the GdAl 2 [1] and the other RM 2 [2, 3] (R — rare earth, M — metal) have been the subject of the extensive experimental as well as theoretical studies [4-7]. Monocrystalline GdAl2 below 171 K orders ferromagnetically and shows resistivity about 100 μΩ cm [3]. A rather high (7.2B) saturation magnetic moment per Gd atom and sufficiently strong mobility of conducting electrons causes that this substance is a prototype material for testing applicability of whole s-f, s-d [8, 9] family of models. With the help of those models, applying the simplest approximations it was easy to get satisfactory quantitative description of the static magnetic properties, conductivity, ... for finite temperature. The great progress has been made during the last decade, in the field of uSing local spin density functional theory (LSDFT)for the description of even stuc-