Wide Linearity Range 3D Magnetic Sensor and Angular Position Detector Based on a Single FePt Spin-Orbit Torque Device.

Three-dimensional (3D) vector magnetic sensors play a significant role in a variety of industries, especially in the automotive industry, which enables the control of precise position, angle, and rotation of motion elements. Traditional 3D magnetic sensors integrate multiple sensors with their sensing orientations along the three coordinate axes, leading to a large size and inevitable nonorthogonal misalignment. Here, we demonstrate a wide linearity range 3D magnetic sensor utilizing a single L10-FePt Hall-bar device, whose sensitivity is 291 VA-1 T-1 in the z-axis and 27 VA-1 T-1 in the in-plane axis. Based on the spin-orbit torque-dominated magnetization reversal, the linear response of anomalous Hall resistance within a large linear range (±200 Oe) for the x, y, and z components of magnetic fields has been obtained, respectively. Typically, it exhibits a relatively lower magnetic noise level of 7.9 nV at 1 Hz than previous results, improving measurement resolution at the low frequency. Furthermore, we provide a straightforward approach for noncontact angular position detection based on a single Hall-bar device, which shows great potential for application in rotational motion control.

Hyaluronic acid functionalized iron-platinum nanoparticles for photothermal therapy and photoacoustic imaging.

This study represents an innovative approach to construct multi-functional nanoplatforms for cancer diagnosis and therapy by combining hyaluronic acid (HA) with iron-platinum nanoparticles (FePt NPs). These HA-coated FePt NPs, referred to as FePt@HA NPs, demonstrated remarkable biocompatibility, high absorption, and excellent light-to-heat conversion properties in the near-infrared (NIR) region, making them ideal candidates for photothermal therapy (PTT). In vitro studies revealed their effective cancer cell eradication under NIR laser irradiation, while in vivo experiments on mice showcased their superior heating capabilities. Moreover, FePt@HA NPs exhibited a distinct and strong photoacoustic (PA) signal, facilitating enhanced and precise intra-tumoral PA imaging. Our results highlight the potential of FePt@HA NPs as promising photothermal agents for future PTT applications. They offer high selectivity, precision, and minimal side effects in cancer treatment, along with their valuable PA imaging application for tumor localization and characterization.

Morphology and Phase Compositions of FePt and CoPt Nanoparticles Enriched with Noble Metal.

The article reveals for the first time the features of nanoparticle morphology, phase compositions, and their changes when heating FePt and CoPt nanoalloys. Nanoparticles were obtained by co-reduction of precursor solution mixtures with hydrazine hydrate. The features were found by a complex of methods of X-ray diffraction (in situ XRD and X-ray scattering), TEM HR, and cyclic voltammetry. In addition, adsorbometry results were obtained, and the stability of different nanocluster structures was calculated by the molecular dynamics method. There were only FCC solid solutions in the X-ray patterns of the FePt and CoPt nanoalloys. According to XRD, in the case of nanoparticle synthesis with Fe and Co content less than 10 at. %, the composition of solid solutions was close to or practically equal to the composition of the as-synthesized nanoparticles quantified by inductively coupled plasma optical emission spectrometry. For systems synthesis with Fe and Co content greater than the above, the solubility limits (SLs) of Fe and Co in Pt were set 11.4 ± 0.7 at. % and 17.5 ± 0.6 at. %, respectively. Therefore, there were non-registered XRD extra-phases (XRNDPh-1) in the systems when CFe,Co ≥ SL. This statement was supported by the results of TEM HR and X-ray scattering: the smallest nanocrystals (1-2 nm) and amorphous particles were found, which qualitatively agreed with the sorbometry and SAXS results. Molecular dynamics calculations of stability for FePt and CoPt alloys claimed the structures of the most stable phase corresponded to phase diagrams (A1 and L12). Specific peculiarities of the morphology and compositions of the solid solutions of nanoalloys were established: structural blockiness (domain) and composition heterogeneity, namely, platinum enrichment of internal (deep) layers and homogenization of the nanoalloy compositions at relatively low temperatures (130-200 °C). The suggested model of the formation of nanoalloys during the synthesis, qualitatively, was compliant with the results of electrochemical deposition of FePt films on the surface of various electrodes. When nanocrystals of solid solutions (C(Fe, Co) < SL) were heated above specific temperatures, there were phase transformations with the formation of two-phase regions, with solid solutions enriched with platinum or iron (non-registered XRD phase XRNDPh-2). The newly formed phase was most likely intermetallic compounds, FePt3, CoPt3. As a result of the study, the model was developed, taking into account the nanoscale of the particles: XRDPh (A1, FeaPt1-a) → XRDPh (A1, Fem×a-xPtm-m×a+x) + XRNDPh-2 (Fen×a+yPtn-n×a-y) (here, m + n = 1, m ≤ 1, n ≤ 1).

High-frequency ultrasound imaging for monitoring the function of meningeal lymphatic system in mice.

The meningeal lymphatic system drains the cerebrospinal fluid from the subarachnoid space to the cervical lymphatic system, primarily to the deep cervical lymph nodes. Perturbations of the meningeal lymphatic system have been linked to various neurologic disorders. A method to specifically monitor the flow of meningeal lymphatic system in real time is unavailable. In the present study, we adopted the high-frequency ultrasound (HFUS) with 1,1'diocatadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI)-loaded microbubble and FePt@PLGA nanoparticle contrast agents to evaluate the flow of the meningeal lymphatic system in 2-month-old mice. Statistical analysis was performed to identify changes of HFUS signals among the microbubbles, FePt@PLGA nanoparticles, and saline control groups. Approximately 15 min from the start of intracerebroventricular injection of contrast agents, their signals were evident at the deep cervical lymph nodes and lasted for at least 60 min. These signals were validated on the basis of the presence of DiI and Fe signals in the deep cervical lymph nodes. Ligation of afferent lymphatic vessels to the deep cervical lymph nodes eliminated the HFUS signals. Moreover, ablation of lymphatic vessels near the confluence of sinuses decreased the HFUS signals in the deep cervical lymph nodes. Glioma-bearing mice that exhibited reduced lymphatic vessel immunostaining signals near the confluence of sinuses had lowered HFUS signals in the deep cervical lymph nodes within 60 min. The proposed method provides a minimally invasive approach to monitor the qualities of the meningeal lymphatic system in real time as well as the progression of the meningeal lymphatic system in various brain disease animal models.

Terahertz permeability of hard ferromagnetic L10-FePt alloy nanowire.

It is commonly thought that ferromagnetic materials can not find applications in terahertz domain because of their very weak dynamic magnetic responses. However, our results in this paper show that the terahertz (THz) permeability of an isolated L10-FePt alloy nanowire with super hard ferromagnetic properties is significant at 0.348 THz, as long as it is at proper remanent states (for instance, Mr/Ms = 1.0), which are ever thought only possible in some metamaterials. Compared to the gigahertz (GHz) permeability of single Fe nanowire, the THz permeability spectra of L10-FePt are shown obviously different. Unusual negative imaginary parts of permeability (µâ€³ < 0) is found related to the equivalent negative damping constant, which is explained from the perspective of abnormal precession of natural resonance at THz for FePt nanowire.

Magnetically guided theranostics: montmorillonite-based iron/platinum nanoparticles for enhancing in situ MRI contrast and hepatocellular carcinoma treatment.

In Asia, including Taiwan, malignant tumors such as Hepatocellular carcinoma (HCC) one of the liver cancer is the most diagnosed subtype. Magnetic resonance imaging (MRI) has been a typical diagnostic method for accurately diagnosing HCC. When it is difficult to demonstrate non-enhanced MRI of tumors, radiologists can use contrast agents (such as Gd3+, Fe3O4, or FePt) for T1-weighted and T2-weighted imaging remain in the liver for a long time to facilitate diagnosis via MRI. However, it is sometimes difficult for T2-weighted imaging to detect small tumor lesions because the liver tissue may absorb iron ions. This makes early cancer detection a challenging goal. This challenge has prompted current research to create novel nanocomposites for enhancing the noise-to-signal ratio of MRI. To develop a method that can more efficiently diagnose and simultaneously treat HCC during MRI examination, we designed a functionalized montmorillonite (MMT) material with a porous structure to benefit related drugs, such as mitoxantrone (MIT) delivery or as a carrier for the FePt nanoparticles (FePt NPs) to introduce cancer therapy. Multifunctional FePt@MMT can simultaneously visualize HCC by enhancing MRI signals, treating various diseases, and being used as an inducer of magnetic fluid hyperthermia (MFH). After loading the drug MIT, FePt@MMT-MIT provides both MFH treatment and chemotherapy in one nanosystem. These results ultimately prove that functionalized FePt@MMT-MIT could be integrated as a versatile drugs delivery system by combining with MRI, chemotheraeutic drugs, and magnetic guide targeting.

Investigation of Flexible Arrayed Lactate Biosensor Based on Copper Doped Zinc Oxide Films Modified by Iron-Platinum Nanoparticles.

Potentiometric biosensors based on flexible arrayed silver paste electrode and copper-doped zinc oxide sensing film modified by iron-platinum nanoparticles (FePt NPs) are designed and manufactured to detect lactate in human. The sensing film is made of copper-doped zinc oxide (CZO) by a radio frequency (RF) sputtering system, and then modified by iron-platinum nanoparticles (FePt NPs). The surface morphology of copper-doped zinc oxide (CZO) is analyzed by scanning electron microscope (SEM). FePt NPs are analyzed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The average sensitivity, response time, and interference effect of the lactate biosensors are analyzed by voltage-time (V-T) measurement system. The electrochemical impedance is analyzed by electrochemical impedance spectroscopy (EIS). The average sensitivity and linearity over the concentration range 0.2-5 mM are 25.32 mV/mM and 0.977 mV/mM, respectively. The response time of the lactate biosensor is 16 s, with excellent selectivity.

An Advanced In Situ Magnetic Resonance Imaging and Ultrasonic Theranostics Nanocomposite Platform: Crossing the Blood-Brain Barrier and Improving the Suppression of Glioblastoma Using Iron-Platinum Nanoparticles in Nanobubbles.

Glioblastoma (GBM) is one of the deadliest and most invasive brain cancers/gliomas, and there is currently no established way to treat this disease. The treatment of GBM typically involves intracranial surgery followed by chemotherapy. However, the blood-brain barrier (BBB) impedes the delivery of the chemotherapeutic drug, making the treatment challenging. In this study, we embedded a chemotherapeutic drug and other nanomaterials into a nanobubble (NB), utilized active tracking and other guidance mechanisms to guide the nanocomposite to the tumor site, and then used high-intensity focused ultrasound oscillation to burst the nanobubbles, generating a transient cavitation impact on the BBB and allowing the drug to bypass it and reach the brain. FePt enhances the resolution of T2-weighted magnetic resonance imaging images and has magnetic properties that help guide the nanocomposite to the tumor location. FePt nanoparticles were loaded into the hydrophobic core of the NBs along with doxorubicin to form a bubble-based drug delivery system (Dox-FePt@NB). The surface of the NBs is modified with a targeting ligand, transferrin (Dox-FePt@NB-Tf), giving the nanocomposite active tracking abilities. The Dox-FePt@NB-Tf developed in the present study represents a potential breakthrough in GBM treatment through improved drug delivery and biological imaging.

Formation and Application of Core-Shell of FePt-Au Magnetic-Plasmonic Nanoparticles.

Monodispersed FePt core and FePt-Au core-shell nanoparticles (NPs) have been chemically synthesized in liquid solution and with controllable surface-functional properties. The NP size was increased from 2.5 nm for FePt to 6.5 nm for FePt-Au, which could be tuned by the initial concentration of gold acetate coated onto FePt seeding NPs via a seed-mediated formation of self-assembled core-shell nanostructures. The analyses of the interplanar spacing obtained from the high-resolution transmission electron microscopy (HRTEM), selective electron diffraction pattern (SAED), and x-ray diffraction (XRD) confirmed that both FePt core and Au shell belong to the face-centered cubic (fcc) structure. FePt-Au NPs have a surface plasmon resonance (SPR) peak at 528 nm in the visible optical band region, indicating the red shift compared with the typical theoretical value of 520 nm of pure Au NPs. The surface modification and ligand exchange of FePt-Au was using mercaptoacetic acid (thiol) as a phase transfer reagent that turned the NPs hydrophilic due to the functional carboxyl group bond on the surface of presented multifunctional magnetic-plasmonic NPs. The water-dispersible FePt-based NPs conjugated with biomolecules could reach the different biocompatibility requirements and also provide enough heating response that acted as a potential agent for magnetic fluid hyperthermia in biomedical engineering research fields.

Micron-Scale Anomalous Hall Sensors Based on FexPt1-x Thin Films with a Large Hall Angle and near the Spin-Reorientation Transition.

In this work, we fabricate and characterize an energy-efficient anomalous Hall sensor based on soft-magnetic FexPt1-x thin films with a large anomalous Hall angle. By varying the composition of the FexPt1-x alloy, its layer thickness and interfacial materials, the magnetization is tuned to be near the spin transition between the perpendicular and in-plane reorientations. We performed magneto-transport and noise characterizations on anomalous Hall sensors with a small sensing area of 20 × 20 µm2 in the 180 to 350 K temperature range. We found the best performance in a 1.25-nm-thick Fe0.48Pt0.52 sandwiched by two 1.6-nm-thick MgO layers at room temperature. The sensor has a large anomalous Hall angle of 1.95%. Moreover, it has the best field detectability of 237.5 nT/√Hz at 1 Hz and 15.3 nT/√Hz at 10 kHz, as well as a high dynamic reserve of 112.0 dB. These results suggest that the FexPt1-x alloy system is suitable for energy-efficient anomalous Hall sensors, particularly in micro-sensing applications.

Influence of Cu on the Improvement of Magnetic Properties and Structure of L10 FePt Nanoparticles.

L10 ordered FePt and FePtCu nanoparticles (NPs) with a good dispersion were successfully fabricated by a simple, green, one-step solid-phase reduction method. Fe (acac)3, Pt (acac)2, and CuO as the precursors were dispersed in NaCl and annealed at different temperatures with an H2-containing atmosphere. As the annealing temperature increased, the chemical order parameter (S), average particle size (D), coercivity (Hc), and saturation magnetization (Ms) of FePt and FePtCu NPs increased and the size distribution range of the particles became wider. The ordered degree, D, Hc, and Ms of FePt NPs were greatly improved by adding 5% Cu. The highest S, D, Hc, and Ms were obtained when FePtCu NPs annealed at 750 °C, which were 0.91, 4.87 nm, 12,200 Oe, and 23.38 emu/g, respectively. The structure and magnetic properties of FePt and FePtCu NPs at different annealing temperatures were investigated and the formation mechanism of FePt and FePtCu NPs were discussed in detail.

Magneto-Electrically Enhanced Intracellular Catalysis of FePt-FeC Heterostructures for Chemodynamic Therapy.

Intracellular catalytic reactions can tailor tumor cell plasticity toward high-efficiency treatments, but the application is hindered by the low efficiency of intracellular catalysis. Here, a magneto-electronic approach is developed for efficient intracellular catalysis by inducing eddy currents of FePt-FeC heterostructures in mild alternating magnetic fields (frequency of f = 96 kHz and amplitude of B ≤ 70 mT). Finite element simulation shows a high density of induced charges gathering at the interface of FePt-FeC heterostructure in the alternating magnetic field. As a result, the concentration of an essential coenzyme-ß-nicotinamide adenine dinucleotide-in cancer cells is significantly reduced by the enhanced catalytic hydrogenation reaction of FePt-FeC heterostructures under alternating magnetic stimulation, leading to over 80% of senescent cancer cells-a vulnerable phenotype that facilitates further treatment. It is further demonstrated that senescent cancer cells can be efficiently killed by the chemodynamic therapy based on the enhanced Fenton-like reaction. By promoting intracellular catalytic reactions in tumors, this approach may enable precise catalytic tumor treatment.

3D Microprinting of Iron Platinum Nanoparticle-Based Magnetic Mobile Microrobots.

Wireless magnetic microrobots are envisioned to revolutionize minimally invasive medicine. While many promising medical magnetic microrobots are proposed, the ones using hard magnetic materials are not mostly biocompatible, and the ones using biocompatible soft magnetic nanoparticles are magnetically very weak and, therefore, difficult to actuate. Thus, biocompatible hard magnetic micro/nanomaterials are essential toward easy-to-actuate and clinically viable 3D medical microrobots. To fill such crucial gap, this study proposes ferromagnetic and biocompatible iron platinum (FePt) nanoparticle-based 3D microprinting of microrobots using the two-photon polymerization technique. A modified one-pot synthesis method is presented for producing FePt nanoparticles in large volumes and 3D printing of helical microswimmers made from biocompatible trimethy- lolpropane ethoxylate triacrylate (PETA) polymer with embedded FePt nanoparticles. The 30 µm long helical magnetic microswimmers are able to swim at speeds of over five body lengths per second at 200 Hz, making them the fastest helical swimmer in the tens of micrometer length scale at the corresponding low- magnitude actuation fields of 5-10 mT. It is also experimentally in vitro verified that the synthesized FePt nanoparticles are biocompatible. Thus, such 3D-printed microrobots are biocompatible and easy to actuate toward creating clinically viable future medical microrobots.

Dependence of the Growth Mode in Epitaxial FePt Films on Surface Free Energy.

Epitaxial thin films of L10-ordered FePt alloys are one of the most important materials in magnetic recording and spintronics applications due to their large perpendicular magnetic anisotropy (PMA). The key to the production of these required superior properties lies in the control of the growth mode of the films. Further, it is necessary to distinguish between the effect of lattice mismatch and surface free energy on the growth mode because of their strong correlation. In this study, the effect of surface free energy on the growth mode of FePt epitaxial films was investigated using MgO, NiO, and MgON surfaces with almost the same lattice constant to exclude the effect of lattice mismatch. It was found that the growth mode can be tuned from a three-dimensional (3D) island mode on MgO to a more two-dimensional (2D)-like mode on MgON and NiO. Contact angle measurements revealed that MgON and NiO show larger surface free energy than MgO, indicating that the difference in the growth mode is due to their larger surface free energy. In addition, MgON was found to induce not only a flat surface as FePt grown on SrTiO3 (STO), which has a small lattice mismatch, but also a larger PMA than that of STO/FePt. As larger lattice mismatch is favored to induce a higher PMA into the FePt films, MgO substrates are exclusively used, but 3D island growth is indispensable. This work demonstrates that tuning the surface free energy enables us to achieve a large PMA and flat film surface in FePt epitaxial films on MgO. The results also indicate that modifying the surface free energy is pertinent for the flexible functional design of thin films.

Overcoming Radiation Resistance by Iron-Platinum Metal Alloy Nanoparticles in Human Copper Transport 1-Overexpressing Cancer Cells via Mitochondrial Disturbance.

BACKGROUND: Radiation therapy remains an important treatment modality in cancer therapy, however, resistance is a major problem for treatment failure. Elevated expression of glutathione is known to associate with radiation resistance. We used glutathione overexpressing small cell lung cancer cell lines, SR3A-13 and SR3A-14, established by transfection with γ-glutamylcysteine synthetase (γ-GCS) cDNA, as a model for investigating strategies of overcoming radiation resistance. These radiation-resistant cells exhibit upregulated human copper transporter 1 (hCtr1), which also transports cisplatin. This study was initiated to investigate the effect and the underlying mechanism of iron-platinum nanoparticles (FePt NPs) on radiation sensitization in cancer cells. MATERIALS AND METHODS: Uptakes of FePt NPs in these cells were studied by plasma optical emission spectrometry and transmission electron microscopy. Effects of the combination of FePt NPs and ionizing radiation were investigated by colony formation assay and animal experiment. Intracellular reactive oxygen species (ROS) were assessed by using fluorescent probes and imaged by a fluorescence-activated-cell-sorting caliber flow cytometer. Oxygen consumption rate (OCR) in mitochondria after FePt NP and IR treatment was investigated by a Seahorse XF24 cell energy metabolism analyzer. RESULTS: These hCtr1-overexpressing cells exhibited elevated resistance to IR and the resistance could be overcome by FePt NPs via enhanced uptake of FePt NPs. Overexpression of hCtr1 was responsible for the increased uptake/transport of FePt NPs as demonstrated by using hCtr1-transfected parental SR3A (SR3A-hCtr1-WT) cells. Increased ROS and drastic mitochondrial damages with substantial reduction of oxygen consumption rate were observed in FePt NPs and IR-treated cells, indicating that structural and functional insults of mitochondria are the lethal mechanism of FePt NPs. Furthermore, FePt NPs also increased the efficacy of radiotherapy in mice bearing SR3A-hCtr1-WT-xenograft tumors. CONCLUSION: These results suggest that FePt NPs can potentially be a novel strategy to improve radiotherapeutic efficacy in hCtr1-overexpressing cancer cells via enhanced uptake and mitochondria targeting.

Annealing Condition Effects on the Structural Properties of FePt Nanoparticles Embedded in MgO via Pulsed Laser Deposition.

FePt nanoparticles (NPs) were embedded into a single-crystal MgO host by pulsed laser deposition (PLD). It was found that its phase, microstructures and physical properties were strongly dependent on annealing conditions. Annealing induced a remarkable morphology variation in order to decrease its total free energy. H2/Ar (95% Ar + 5% H2) significantly improved the L10 ordering of FePt NPs, making magnetic coercivity reach 37 KOe at room temperature. However, the samples annealing at H2/Ar, O2, and vacuum all showed the presence of iron oxide even with the coverage of MgO. MgO matrix could restrain the particles' coalescence effectively but can hardly avoid the oxidation of Fe since it is extremely sensitive to oxygen under the high-temperature annealing process. This study demonstrated that it is essential to anneal FePt in a high-purity reducing or ultra-high vacuum atmosphere in order to eliminate the influence of oxygen.

Multifunctional CNTs-PAA/MIL101(Fe)@Pt Composite Membrane for High-throughput Oily Wastewater Remediation.

A surge of effort has been devoted to establishing super-wetting membranes with versatility for oily waste water purification. However, persistent challenge remains the lower separation flux. Moreover, the majorities of catalysts are only adsorbed on the surface and easily fall off after multiple cyclic separations. In this work, an effective strategy has been taken to construct a composite membrane consisting of polyacrylic acid functionalized carbon nanotubes (CNTs-PAA) and MIL101(Fe)@platinum nanoparticles (MIL101(Fe)@Pt NPs). The obtained CNTs-PAA/MIL101(Fe)@Pt composite membrane can achieve degradation of dye molecules and at the same time effective separation of oil-in-water emulsions. The separation throughput of this composite membrane can reach up to 11000 L m-2 h-1 bar-1, which has exceeded most of the previous reported multifunctional separation membranes. Furthermore, this composite membrane has presented stable mechanical property and excellent anti-corrosion ability. This work gives comprehensive consideration to excellent separation performance, versatility and stability, which could have potential applications in practical oily wastewater treatment.

First-principles study of electronic structure and magnetic properties of L10-ordered FeNi, FePd, and FePt alloys.

The structural, electronic, and magnetic properties of three spin configurations of L10-ordered FeM alloys (M = Ni, Pd, or Pt) were studied using the first-principles method. The calculations were carried out using Quantum ESPRESSO package within the framework of Density Functional Theory (DFT). The exchange-correlation functional potentials were studied using local density approximation (LDA) of Perdew-Zunger (PZ), the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE), Perdew and Wang 91 (PW91), and Perdew-Burke-Ernzerhof revised for solids (PBEsol). We found that the PBE approximation has the most accurate results for lattice parameters compared to the experimental values. Furthermore, our results reveal that the most stable spin configuration for the considered alloys is the ferromagnetic configuration, where all spins are aligned perpendicular to the (001) plane. However, in FePd and FePt alloys, a small variation in the tetragonality ratio c/a (from 0.98 to 0.92) can transform them from ferromagnetic to antiferromagnetic state. In an antiferromagnetic state, a pseudogap is observed just below fermi energy for each alloy. Moreover, our calculations reveal large magnetocrystalline anisotropies for FePt alloy in the order of 3 meV/f.u. On the other hand, FePd and FeNi show relatively lower values in the range of 0.18-0.42 meV/f.u. Finally, Heisenberg exchange interactions are calculated from first-principles and Green's functions formalism.

Evolution of the Structural and Magnetic Properties of Bulk Fe61Co10B20W1Y8-XPtx Alloys through the Partial Substitution of Pt for Y.

This paper presents the results of an investigation into rapidly quenched Fe-based alloys with the chemical formula: Fe61Co10B20W1Y8-xPtx (where x = 3, 4, 5). In these alloys, a small quantity of Pt was added, and the Y content was reduced concurrently. Samples of the aforementioned alloys were injection-cast in the form of plates with the dimensions: 0.5 mm × 10 mm × 10 mm. The resulting structure was examined using X-ray diffractometry (XRD), Mössbauer spectroscopy and scanning electron microscopy (SEM). The results of the structural research reveal that, with a small addition of Pt, areas rich in Pt and Y are created-in which Fe-Pt and Pt-Y compounds, with different crystallographic systems, are formed. It has also been shown that an increase in Pt content, at the expense of Y, contributed to the formation of fewer crystalline phases, i.e., it allowed a material with a more homogeneous structure to be obtained. Magnetic properties of the Fe61Co10B20W1Y8-xPtx (where x = 3, 4, 5) alloy samples were tested using a vibrating sample magnetometer (VSM). The magnetic properties of the investigated materials revealed that the saturation magnetisation increased with increasing Pt content, at the expense of Y. This effect is due to the occurrence of different proportions of crystalline magnetic phases within the volume of each alloy.

Magnetic Phase Coexistence and Hard-Soft Exchange Coupling in FePt Nanocomposite Magnets.

With the aim of demonstrating phase coexistence of two magnetic phases in an intermediate annealing regime and obtaining highly coercive FePt nanocomposite magnets, two alloys of slightly off-equiatomic composition of a binary Fe-Pt system were prepared by dynamic rotation switching and ball milling. The alloys, with a composition Fe53Pt47 and Fe55Pt45, were subsequently annealed at 400 °C and 550 °C and structurally and magnetically characterized by means of X-ray diffraction, 57Fe Mössbauer spectrometry and Superconducting Quantum Interference Device (SQUID) magnetometry measurements. Gradual disorder-order phase transformation and temperature-dependent evolution of the phase structure were monitored using X-ray diffraction of synchrotron radiation. It was shown that for annealing temperatures as low as 400 °C, a predominant, highly ordered L10 phase is formed in both alloys, coexisting with a cubic L12 soft magnetic FePt phase. The coexistence of the two phases is evidenced through all the investigating techniques that we employed. SQUID magnetometry hysteresis loops of samples annealed at 400 °C exhibit inflection points that witness the coexistence of the soft and hard magnetic phases and high values of coercivity and remanence are obtained. For the samples annealed at 500 °C, the hysteresis loops are continuous, without inflection points, witnessing complete exchange coupling of the hard and soft magnetic phases and further enhancement of the coercive field. Maximum energy products comparable with values of current permanent magnets are found for both samples for annealing temperatures as low as 500 °C. These findings demonstrate an interesting method to obtain rare earth-free permanent nanocomposite magnets with hard-soft exchange-coupled magnetic phases.