Room Temperature Saturation Research Articles

Above-room-temperature intrinsic ferromagnetism in ultrathin van der Waals crystal Fe3+xGaTe2

Two-dimensional (2D) van der Waals (vdW) magnets are crucial for ultra-compact spintronics. However, so far, no vdW crystal has exhibited tunable above-room-temperature intrinsic ferromagnetism in the 2D ultrathin regime. Here, we report the tunable above-room-temperature intrinsic ferromagnetism in ultrathin vdW crystal Fe3+xGaTe2 (x = 0 and 0.3). By increasing the Fe content, the Curie temperature (TC) and room-temperature saturation magnetization of bulk Fe3+xGaTe2 crystals are enhanced from 354 to 376 K and 43.9 to 50.4 emu·g−1, respectively. Remarkably, the robust anomalous Hall effect in 3-nm Fe3.3GaTe2 indicates a record-high TC of 340 K and a large room-temperature perpendicular magnetic anisotropy energy of 6.6 × 105 J m−3, superior to other ultrathin vdW ferromagnets. First-principles calculations reveal the asymmetric density of states and an additional large spin exchange interaction in ultrathin Fe3+xGaTe2 responsible for robust intrinsic ferromagnetism and higher TC. This work opens a window for above-room-temperature ultrathin 2D magnets in vdW-integrated spintronics.

Disentangling different interfacial effects of reduced thin layer magnetizations

Abstract Thin buried magnetic layers ranging from thicknesses of a few atomic monolayers to several nanometers are omnipresent in the fields of magnetism and spintronics. For the functionality and fine tuning of devices build with such layers, exact knowledge of the depth dependent magnetic properties is essential. Especially the interfacial magnetic properties are important. Hence, understanding how magnetism is affected by structural variations, such as thickness or interface roughness, is mandatory. In this study, we use x-ray resonant magnetic reflectometry and magnetometry to study the high-resolution depth dependent magnetization profiles of thin magnetic transition metal layers sandwiched between an oxide and chromium layer. Compared to bulk materials, the room temperature saturation magnetization of these layers is reduced by up to 67%. These reductions are extremely sensitive to small structural variations. From the magnetic depth profiles, we disentangle different effects contributing to the magnetization reduction and the exact magnetic properties of the interface.

Structural, magnetic and impedance dynamics of multiferroic high entropy garnet ceramics

We have synthesized (Gd0.2Y0.2Nd0.2Dy0.2R0.2)3Fe5O12(R=Er,Sm and Pr) high entropy garnet ceramic samples via solid-state reaction route for the first time. All the samples are formed in a single phase and exhibit a simple cubic crystal structure with an Ia3‾d space group. The lattice constant of these samples varies as per the ionic radii of the substituted element and ranges in between 12.4458Å to 12.5062Å. The morphology and elemental contributions are also investigated for all the high entropy samples. Additionally, magnetization data reveal a similar value of room temperature saturation magnetization i.e., ∼16emu/g for (Gd0.2Y0.2Nd0.2Dy0.2R0.2)3Fe5O12(R=Sm and Pr) samples and it becomes 13.67emu/g for Er doped sample. This variation is understood with Dionne's sublattice magnetization model where the molecular weight of the substituent will affect the saturation magnetization. Furthermore, a deviation from ideal Debye-type relaxation behavior is noticed in room temperature Nyquist plots for all three samples. An anomaly in the dielectric plot around ferrimagnetic transition temperature indicates the multiferroic behavior of these high entropy ceramic materials.

Excellent intrinsic magnetic properties in the TbCu7-type Sm-Fe-N compound

We report excellent intrinsic magnetic properties of SmFe9Nδ epitaxial thin films with TbCu7-type crystal structure, i.e., room temperature saturation magnetization (μ0Ms) of 1.64 T, Curie temperature (Tc) of 771 K and magnetic anisotropy field (μ0HA) of ∼22 T for δ=1.1, the saturation magnetization of which is superior to that of Sm2Fe17N3 (μ0Ms= 1.57 T) and Nd2Fe14B compounds (μ0Ms= 1.61 T). X-ray diffraction and transmission electron microscopy revealed that the thin films have a highly textured single TbCu7-type phase with its c-axis perpendicular to the film. Heat treatment of the thin films under N atmosphere expands the lattice and increases the unit cell volume of the SmFe9Nδ structure, which also switches the magnetocrystalline anisotropy from easy plane (δ = 0) to easy axis (δ=1.1). Furthermore, the μ0Ms and Tc of SmFe9Nδ films also increased with increasing nitrogen content in the structure, leading to promising intrinsic magnetic properties. Based on this study, we can conclude that the rare-earth lean SmFe9Nδ based TbCu7-type compound has potential for the development of high performance anisotropic bonded magnets with superior performance to that of existing anisotropic Sm2Fe17N3 or Nd-Fe-B bonded magnets.

High magnetoelectric coupling in piezoelectric modified BNT and magnetic NZFO particulate composite

Lead-free magnetoelectric (ME) particulate composite comprising piezoelectric 72.5Bi0·5Na0·5TiO3-22.5Bi0·5K0·5TiO3–5BiMg0·5Ti0·5O3 (MBNT) and piezomagnetic Ni0·7Zn0·3Fe2O4 (NZFO) in varying phase fraction, i.e., (1-x)MBNT-xNZFO (x = 0.05–0.30; Δx = 0.05) was prepared by solid state reaction route. Their structural, electrical, magnetic and ME properties were investigated. The high temperature sustainability up to 390 °C and the relaxor behavior was confirmed by their dielectric study. The room temperature dielectric constant (∼1081 at 1 kHz), saturation polarization (∼37.12 μC/cm2) and electro-strain (∼0.22 %) was observed maximum for pure MBNT, which decreases in composites with the induction of non-ferroelectric NZFO content. All composites exhibited magnetic hysteresis behavior where net increase in magnetization was associated with the relative increase in NZFO that possessed a saturation magnetization of 74.52 emu/g. At the optimum phase fraction of composite (i.e., 0.80MBNT-0.20NZFO), giant ME coefficient (∼58.12 mV/cm.Oe at 800 Oe) was observed at low frequency of 10 Hz, which suggest its credibility for energy harvester.

A Novel Spinel Ferrite-Hexagonal Ferrite Composite for Enhanced Magneto-Electric Coupling in a Bilayer with PZT.

The magnetoelectric effect (ME) is an important strain mediated-phenomenon in a ferromagnetic-piezoelectric composite for a variety of sensors and signal processing devices. A bias magnetic field, in general, is essential to realize a strong ME coupling in most composites. Magnetic phases with (i) high magnetostriction for strong piezomagnetic coupling and (ii) large anisotropy field that acts as a built-in bias field are preferred so that miniature, ME composite-based devices can operate without the need for an external magnetic field. We are able to realize such a magnetic phase with a composite of (i) barium hexaferrite (BaM) with high magnetocrystalline anisotropy field and (ii) nickel ferrite (NFO) with high magnetostriction. The BNx composites, with (100 - x) wt.% of BaM and x wt.% NFO, for x = 0-100, were prepared. X-ray diffraction analysis shows that the composites did not contain any impurity phases. Scanning electron microscopy images revealed that, with an increase in NFO content, hexagonal BaM grains become prominent, leading to a large anisotropy field. The room temperature saturation magnetization showed a general increase with increasing BaM content in the composites. NFO rich composites with x ≥ 60 were found to have a large magnetostriction value of around -23 ppm, comparable to pure NFO. The anisotropy field HA of the composites, determined from magnetization and ferromagnetic resonance (FMR) measurements, increased with increasing NFO content and reached a maximum of 7.77 kOe for x = 75. The BNx composite was cut into rectangular platelets and bonded with PZT to form the bilayers. ME voltage coefficient (MEVC) measurements at low frequencies and at mechanical resonance showed strong coupling at zero bias for samples with x ≥ 33. This large in-plane HA acted as a built-in field for strong ME effects under zero external bias in the bilayers. The highest zero-bias MEVC of ~22 mV/cm Oe was obtained for BN75-PZT bilayers wherein BN75 also has the highest HA. The Bilayer of BN95-PZT showed a maximum MEVC ~992 mV/cm Oe at electromechanical resonance at 59 kHz. The use of hexaferrite-spinel ferrite composite to achieve strong zero-bias ME coupling in bilayers with PZT is significant for applications related to energy harvesting, sensors, and high frequency devices.

High-Temperature Ferroic Glassy States in SrTiO_{3}-Based Thin Films.

Disordered ferroics hold great promise for next-generation magnetoelectric devices because their lack of symmetry constraints implies negligible hysteresis with low energy costs. However, the transition temperature and the magnitude of polarization and magnetization are still too low to meet application requirements. Here, taking the prototype perovskite of SrTiO_{3} as an instance, we realize a coexisting spin and dipole reentrant glass states in SrTiO_{3} homoepitaxial films via manipulation of local symmetry. Room-temperature saturation magnetization and spontaneous polarization reach ∼ 10 emu/cm^{3} and ∼ 25 μC/cm^{2}, respectively, with high transition temperatures (101K and 236K for spin and dipole glass temperatures and 556K and 1100K for Curie temperatures, respectively). Our atomic-scale investigation points out an underlying mechanism, where the Ti/O-defective unit cells break the local translational and orbital symmetry to drive the formation of unusual slush states. This study advances our understanding of the nature of the intricate couplings of ferroic glasses. Our approach could be applied to numerous perovskite oxides for the simultaneous control of the local magnetic and polar orderings and for the exploration of the underlying physics.

CA and/or EDTA functionalized magnetic iron oxide nanoparticles by oxidative precipitation from FeCl2 solution: structural and magnetic study

Four samples containing magnetic iron oxide nanoparticles (MIONs) of various sizes are prepared employing a simple low-temperature method of oxidative precipitation from FeCl2∙4H2O–NaOH–NaNO3 aqueous solution. For the preparation of two samples, the usual oxidation-precipitation synthesis protocol is modified by using ethylenediaminetetraacetic acid (EDTA) chelating agent as a stabilizer of the Fe2+ ions in a solution, which results in the partial capping of the prepared MIONs with EDTA molecules. Three out of four samples are subjected to citric acid (CA) functionalization in the post synthesis protocol. Structural and magnetic properties of the synthesized MIONs are assessed using various experimental techniques (XRD, TEM, Fourier transform infrared, dynamic light scattering, Mössbauer, and SQUID). The average size of spherical-like MIONs is tuned from 7 nm to 38 nm by changing the synthesis protocol. Their room temperature saturation magnetization, M s, is in the range of 43 to 91 emu g−1. Magnetic heating ability, expressed via specific absorption rate value, which ranges from 139 to 390 W/gFe, is discussed in relation to their structural and magnetic properties and the possible energy dissipation mechanisms involved. The best heating performance is exhibited by the sample decorated with EDTA and with a bimodal size distribution with average particle sizes of 14 and 37 nm and M s = 87 emu g−1. Though this sample contains particles prone to form aggregates, capping with EDTA provides good colloidal stability of this sample, thus preserving the magnetic heating ability. It is demonstrated that two samples, consisting of 7 nm-sized CA- or 14 nm-sized EDTA/CA-functionalized superparamagnetic MIONs, with a similar hydrodynamic radius, heat in a very similar way in the relatively fast oscillating alternating current magnetic field, f = 577 kHz.

Flexomagnetic Effect Enhanced Ferromagnetism and Magnetoelectrochemistry in Freestanding High-Entropy Alloy Films.

Freestanding thin films of functional materials enable the tuning of properties via strain and strain gradients, broadening their applications. Here, a systematic approach is proposed to fabricate freestanding CrMnFeCoNi high-entropy alloy (HEA) thin films by pulsed laser deposition using expansion-contraction of NaCl substrates and weak van der Waals interaction of the interface, which form wrinkles with inhomogeneous strain gradients when transferred to a viscous handle. We demonstrate that the nonuniform gradients of external strain (flexomagnetic effect) can induce the partial structural phase transition from FCC to BCC in the wrinkled HEA film, resulting in a 10-fold increase in its room-temperature saturation magnetization compared with the unstrained flat HEA film. Furthermore, after applying an external magnetic field, due to the different electron transfer behavior caused by the electron scattering in wrinkled and flat HEA films, their electrocatalytic magnetic responses showed a diametrically opposite picture. Our work provides a promising strategy for tuning physical and chemical properties via complex strained geometries.

Mesoporous CoFe2O4 nanocrystals: Rapid microwave-hydrothermal synthesis and effect of synthesis temperature on properties

Cobalt ferrite (CoFe2O4) nanoparticles of the size of 7–20 nm have been easily synthesized by microwave-hydrothermal route with rapid heating at 100, 150, and 200 °C. The XRD and TEM studies establish that the pure spinel CoFe2O4 phase is obtained at all the synthesis temperatures. FTIR examination presents the bands representative of cubic CoFe2O4 phase and triton X-100 surfactant. Thermal analysis shows nominal weight loss between 25 and 1000 °C demonstrating high thermal stability of the samples. Electron microscopy examination reveals spherical morphology with the particle size increasing as the synthesis temperature increases. The EDX spectrum reveals the stoichiometric proportion to be nearly 1:2 for Co: Fe as anticipated, and the elemental mapping results show the extreme distribution of elements Co, Fe, and O. The SAED patterns show bright and distinct diffraction rings associated with the different lattice planes of cubic CoFe2O4 phase. The clear lattice fringes in HRTEM images endorse the single-crystalline nature of the nanoparticles. N2 sorption studies demonstrate mesoporous structure with specific surface area decreasing with rising synthesis temperature. These nanoparticles exhibit hysteretic magnetization at room temperature, characteristic of the ferrimagnetic material, with the room temperature saturation magnetization close to that of bulk CoFe2O4. The MS value increases, but Mr and Hc values decrease as the synthesis temperature/particle size increases. It is anticipated that the findings of this study will offer more insight into the effective use of microwave-hydrothermal synthesis to tailor the properties of CoFe2O4 nanoparticles for applications.

Magnetic, magnetodielectric, and magnetoimpedance correlations in co-substituted (Co, Ho) KBiFe2O5 at room temperature

The exotic physical properties of unique brownmillerite KBiFe2O5 (HC0) are enhanced by co-substituting rare-earth Holmium (Ho) and transition metal Cobalt (Co), ion and establishing their interaction. Dielectric, structural, magnetic, magnetodielectric (MD), and magnetoimpedance (MI) properties of co-substituted KBi1−xHoxFe2(1−y)CoyO5 [x = y = 0, 0.05, 0.1, & 0.15] are investigated. The solid-state reaction method is used to synthesize, and the Rietveld refined powder X-ray diffraction patterns confirm the monoclinic structure with the P2/c space group. The Raman shift decreases, but the lattice strain increases with increased co-doping and correlates with MD data. The room temperature (RT) remnant (MR) and saturation (MS) magnetization increase by ∼ 20 and ∼ 2 times, respectively, with co-doping. The magnetic anomaly near dielectric transition (∼ 500 °C for KBi0.95Ho0.05Fe1.9Co0.05O5) suggests the signature of MD coupling for the co-doped samples. The MD and magneto-loss (ML) strength of HC0 increase with co-doping from 0.35 % to 0.65 % and 0.65 % to 1.25 %, respectively. In addition, the MD coupling coefficient increases from 4 % to 11 %, with the increase in co-doping. The RT MI curve of KBi0.85Ho0.15Fe1.75Co0.15O5 (HC15) shows an enhanced symmetric hysteresis loop (butterfly-like) with a maximum strength of ∼ 0.6 %. The frequency-dependent MD of HC0 shows that the maximum MD% at a high frequency (> 50 kHz) is enhanced with the increase in co-doping, and the corresponding MD and ML strength of HC15 are − 1.2 % and − 0.4 %, respectively. The dielectric relaxation time for HC15 shows maximum non-linear variation with the magnetic field, suggesting an intrinsic contribution to MD coupling. The observed dielectric transition (TC) around 510 °C of HC0 decreases to 480 °C (for HC15) with the increase in the co-doping. Thus, enhanced MD coupling and magnetic field-controlled dielectric relaxation for co-doped HC0 make this material suitable for next-generation spintronic and storage device applications.

Effect of pH value on multiferroic properties of barium ferrite ceramics prepared by sol–gel method

In this paper, BaFe12O19 (BaM) ceramics at different pH values were prepared by sol–gel method. Effects of pH value on the microstructure, electrical as well as magnetic properties were systematically studied. XRD indicate that the ceramics were mainly BaM. However, with the pH value increasing further, the BaFe2O4 impurity phase appears gradually in both powders and ceramics due to the degree of complexation between citric acid and metal cations and other reasons. SEM results show that the grain size of ceramics decreases from 2.28 μm to 1.35 μm with the pH value increase from 4 to 8. It is found that room temperature dielectric constant, residual polarization, and saturation magnetization of the ceramics is the largest when the pH value of the solution is 4, which are 0.108 μC/cm2 and 32.829 emu/g, respectively. The dielectric constant and residual polarization of ceramics decrease with the increase of pH value. The ferroelectric and magnetic hysteresis loops have confirmed room-temperature multiferroic properties of the prepared ceramics. It laid the foundation for the further development of new room temperature single-phase multi-iron materials.

Tuning the photocatalytic performance through magnetization in Co-Zn ferrite nanoparticles

In this work, the link between the photocatalytic performance of Co-Zn ferrite nanoparticles and the net magnetic moment is analyzed. CoxZn1-xFe2O4 nanoparticles (0 ≤ x ≤ 1) were synthesized by co-precipitation method and different physicochemical techniques were employed to characterize the samples (X-ray diffraction, Transmission Electron Microscopy (TEM), BET surface area, Diffuse Reflectance Spectroscopy (DRS), Photoluminescence spectroscopy, Z-potential, SQUID magnetometry). Enhanced photocatalytic degradation (maximum degradation ratios of two emerging pollutants, phenol and toluene) are found in those nanoparticles (0.4 ≤ x ≤ 0.6) with optimum magnetic response (i.e. superparamagnetism at room temperature and high saturation magnetization). The magnetization of the nanoparticles turns out to be the determining factor in the optimization of the photocatalytic response, since there is no clear relationship with other physicochemical parameters (i.e. specific surface area, isoelectric point, band gap energy or photoluminescence). These results support the current field of research related to photocatalytic performance enhancement through magnetic field effects.

Internet of Things- (IoT-) Based Real-Time Vital Physiological Parameter Monitoring System for Remote Asthma Patients

In this paper, the design and implementation of an asthma patient monitoring system are presented. It can be categorized as an IoT-based device which can monitor heart rate, room temperature, humidity, air quality, nostril temperature, and oxygen saturation (SpO2) using an ESP8266 microcontroller and different sensors. All data will be sent to Firebase via Wi-Fi and then to patients and doctors via mobile applications and websites, respectively. Doctors can access this data via a website and instruct patients based on their specific needs. An ESP8266 microcontroller, a DHT11 temperature and humidity sensor, a MAX30100 pulse and SpO2 sensor, a MQ-135 air quality sensor, and an LM-35 temperature sensor have been used for the proposed system in this research. This system uses an efficient way to store all the data and information about the patient. It also carries their various test reports. The data is preserved in a proper way, which will help the patient or doctor retrieve any information in a smooth and swift manner. The software part of the system is divided into two parts. One of them is a mobile application that was designed by the Android Studio. The second one is the website, and it is also divided into two parts. HTML (hypertext markup language), CSS (cascading style sheets), and JavaScripts are designed for the front end of the website, and PHP (hypertext preprocessor) is used for the backend of the website. The device is tested on seven different real human test subjects, and the accuracy of that device is state of the art. It can measure the heart rate of a person along with their oxygen saturation with accuracy. Also, this device calculates the humidity properly as it changes the moment wet towels are put near the sensors and far from the sensors. It also shows the proper air quality as it has been tested with smoke to measure the extreme difference in the air quality. This system also has video calling and prescription features. Using this system, patients can consult with the doctor and get a prescription. Using this system, the vital physiological parameters of the remote patients can be measured and monitored. Any hospital or diagnostic center can be more efficient and organized by using a system. And patients are also freed from the hustle as they do not need to go and visit the doctor over and over again. The system is designed in such a way that it can look after the particular needs of a typical hospital or a diagnostic center and is able to provide easy and efficient storage of information related to patients.

Carbon Dots/Iron Oxide Nanoparticles with Tuneable Composition and Properties.

We present a simple strategy to generate a family of carbon dots/iron oxide nanoparticles (C/Fe-NPs) that relies on the thermal decomposition of iron (III) acetylacetonate in the presence of a highly fluorescent carbon-rich precursor (derived via thermal treatment of ethanolamine and citric acid at 180 °C), while polyethylene glycol serves as the passivation agent. By varying the molar ratio of the reactants, a series of C/Fe-NPs have been synthesized with tuneable elemental composition in terms of C, H, O, N and Fe. The quantum yield is enhanced from 6 to 9% as the carbon content increases from 27 to 36 wt%, while the room temperature saturation magnetization is improved from 4.1 to 17.7 emu/g as the iron content is enriched from 17 to 31 wt%. In addition, the C/Fe-NPs show excellent antimicrobial properties, minimal cytotoxicity and demonstrate promising bioimaging capabilities, thus showing great potential for the development of advanced diagnostic tools.

An investigation on the heat dissipation in Zn-substituted magnetite nanoparticles, coated with citric acid and pluronic F127 for hyperthermia application

Zinc substituted spinel ferrite nanoparticles are appropriate for magnetic fluid hyperthermia. Stable suspensions of Zn2+ substituted magnetite (ZnxFe3-xO4, 0 ≤ x ≤ 0.20) nanoparticles in aqueous solutions (pH 5.5) were synthesized by means of co-precipitation approach, using citric acid (CA) and pluronic F127 as surfactants for hyperthermia application. The specimens were characterized by different methods. XRD patterns of the precipitates confirmed that all specimens have single phase cubic spinel structures and their lattice parameters increased as Zn2+ content increased. Mean crystallite sizes of the uncoated specimens were determined to be around 28 nm, using Scherrer's formula. By increasing the Zn2+ content, Curie temperature of the uncoated specimens reduced from 545 to 410 °C monotonically caused by reduction in super-exchange interactions. Room temperature saturation magnetizations of the uncoated specimens increased to 98.8 emu/g for x = 0.10 initially, and then decreased to 79.6 emu/g for x = 0.20. It is attributed to the replacement of paramagnetic Fe3+ ions by diamagnetic Zn2+ ones and spin canting. FTIR spectra reconfirmed formation of pure magnetite and Zn2+ substituted magnetite nanoparticles and also proved the presence of ligands on the surface of the nanoparticles. TEM investigation showed that mean particle sizes of the coated nanoparticles were in the range of 35–40 nm. The obtained ferrofluids showed a good stability in aqueous medium (pH 5.5) and according to the room temperature magnetic measurements, heating efficiency is scarcely released due to relaxation processes. Maximum obtained specific loss power (SLP) was 539 W/g and that of intrinsic loss power (ILP) was 7.26 nHm2/kg for x = 0.05 (f = 290 kHz, H = 16 kA/m) with a nanoparticle concentration as low as 1.2 mg/ml, which is a promising candidate for magnetic hyperthermia applications potentially.

Unravelling the Anisotropic Behavior of Nickel—Wires Prepared through External Magnetic Field Assisted Hydrazine Reduction Method

Ni wires, prepared through a hydrazine reduction, were exposed to external magnetic fields of different geometrical shape and configuration during the synthesis denoted as Ni-Non-Magnetic, Ni-Double, Ni-Single, Ni-Ring. Their effect on the wire morphology, magnetization and magnetic anisotropy was then investigated via various characterization techniques viz. X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (HR-FESEM), and vibrating sample magnetometer (VSM). The polycrystalline single phase of the Ni-wires with face centered cubic symmetry was confirmed through the analysis of XRD patterns. Analysis of HR-FESEM images revealed that the Ni-particles were aligned in form of wire-like morphology. The Ni-single sample formed the wires with minimum diameter compared to the parent sample. The magnetization measurements performed at 300 K and 50 K demonstrated the ferromagnetic behavior of all the samples. The room temperature saturation magnetization (MS) and anisotropy constant (K) of the Ni-wires were reduced upon providing the external field during synthesis. However, the low temperature (50 K) magnetization behavior was rather opposing, indicating enhanced values of MS and K. Among all, Ni-ring sample showed maximum anisotropy with a value of 3.84 × 104 erg/cm3 at 50 K. The ambiguous nature of the anisotropic constant and saturation magnetization ascribed partly to the variation in diameters of Ni-wires and to the intermittent spin-spin exchange interactions of unaligned/partially aligned particles during the synthesis. Briefly, in the present study, it was established that the morphology and magnetic anisotropy of the Ni-wires could be tailored through the external magnetic field assisted synthesis method.

Magnetism and spin transport in platinum/scandium-substituted terbium iron garnet heterostructures

Growth, structural, magnetic, and spin transport properties of epitaxial scandium-substituted terbium iron garnet (TbScIG) thin films on gadolinium gallium garnet [GGG, (111) orientation] substrates are reported as a function of Sc content. The films are epitaxial on GGG without strain relaxation up to a thickness of 90 nm and exhibit perpendicular magnetic anisotropy. Sc, a nonmagnetic cation, occupies up to 40% of the octahedral Fe sites. Increasing Sc lowers the compensation temperature and Curie temperature and increases the room-temperature saturation magnetization from 37 kA/m for ${\mathrm{Tb}}_{2.8}{\mathrm{Fe}}_{5.2}{\mathrm{O}}_{12}$ to 59 kA/m for ${\mathrm{Tb}}_{2.8}{\mathrm{Sc}}_{0.8}{\mathrm{Fe}}_{4.4}{\mathrm{O}}_{12}$. Anomalous Hall effect-like spin Hall magnetoresistance measurements were performed to determine the effect of scandium content on spin mixing conductance of the TbScIG|Pt interface. The spin mixing conductance increased significantly with an increase in Sc content, consistent with a dependence of spin transport on the net Fe magnetization instead of the total magnetization of the garnet.

Anisotropic Growth and Magnetic Properties of α″-Fe16N2@C Nanocones.

α″-Fe16N2 nanomaterials with a shape anisotropy for high coercivity performance are of interest in potential applications such as rare-earth-free permanent magnets, which are difficult to synthesize in situ anisotropic growth. Here, we develop a new and facile one-pot microemulsion method with Fe(CO)5 as the iron source and tetraethylenepentamine (TEPA) as the N/C source at low synthesis temperatures to fabricate carbon-coated tetragonal α″-Fe16N2 nanocones. Magnetocrystalline anisotropy energy is suggested as the driving force for the anisotropic growth of α″-Fe16N2@C nanocones because the easy magnetization direction of tetragonal α″-Fe16N2 nanocrystals is along the c axis. The α″-Fe16N2@C nanocones agglomerate to form a fan-like microstructure, in which the thin ends of nanocones direct to its center, due to the magnetostatic energy. The lengths of α″-Fe16N2@C nanocones are ~200 nm and the diameters vary from ~10 nm on one end to ~40 nm on the other end. Carbon shells with a thickness of 2–3 nm protect α″-Fe16N2 nanocones from oxidation in air atmosphere. The α″-Fe16N2@C nanocones synthesized at 433 K show a room-temperature saturation magnetization of 82.6 emu/g and a coercive force of 320 Oe.

Effect of atom substitutions on the magnetic properties in Ce2Fe17: Toward permanent magnet applications

Due to the rapidly developing technologies and huge market demand, there has been increasing interest internationally in exploring permanent magnet formulations in addition to the well-known Nd2Fe14B and SmCo5/Sm2Co17. Given Fe's low materials cost and generally high magnetization, Fe-rich rare earth binaries such as Ce2Fe17 comprise a rich “hunting ground” for such new materials. While this compound suffers from a low ordering point and is a helimagnet, these difficulties are easily remedied by the substitution of appropriate amounts of cobalt for Fe, with room-temperature saturation magnetization as high as 1.5 T. Here, we try to switch the all-important magnetic anisotropy from planar to uniaxial behavior in Ce2Fe17 via 18h- and 6c-type atom substitutions with Si, Ir, and numerous other atoms. The uniaxial magnetocrystalline anisotropy is successfully achieved in the 6c-site-substituted Ce2Fe15Ir2 systems, along with large magnetization. We find that iridium substitution, in particular, induces a substantial uniaxial anisotropy of 11.25 MJ/m3, which is comparable to most of the current rare earth permanent magnets. Although the iridium substitution is costly, the finding of Ir-triggered uniaxial magnetic anisotropy indicates the potential of Ce–Fe-based alloys for permanent magnets.