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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Effect of Chromium Substitution on Structural and Magnetic Properties of Nickel-Cobalt Ferrite Nanoparticles Synthesized by Co-precipitation Method

Ni{sub 0.3}Co{sub 0.7}Cr{sub x}Fe{sub 2−x}O{sub 4} (x = 0, 0.2, 0.4, and 0.6) nanoparticles were synthesized by co-precipitation method followed by annealing treatment. The structural and magnetic properties of the samples were determined by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric and differential scanning calorimetry (TG-DSC) analysis, and a vibrating sample magnetometer (VSM) at room temperature. The XRD patterns revealed a single-phase cubic spinel structure for all the annealed products. The average crystallite size is in the range of 45–60 nm. Cation distribution by XRD analysis indicated that Cr{sup 3+} ions preferentially replace Fe{sup 3+} ions from the octahedral sites due to their favorable crystal field effects; with increasing Cr content, it was observed that Co{sup 2+} migrated from octahedral sites to tetrahedral sites. The decrease in saturation magnetization with the increase in Cr concentration could be attributed to reduction in the super-exchange interaction between the A and B sublattices. The observed decrease in coercivity can be explained by reduction in magneto-crystalline anisotropy that resulted from migration of Co{sup 2+} ions from B sites to A sites with the increase in Cr content.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Experimental and Theoretical Investigations of Magnetic Properties of Co Ferrite/Polyvinyl Alcohol Nanocomposites

Cobalt ferrite nanoparticles (NPs) have been synthesized by the modified co-precipitation technique in the presence of the polyvinyl alcohol (PVA) matrix. The structural and magnetic properties of NPs are tunable by means of interaction between the polymer and the surface of NPs. Magnetic properties of NPs were simulated using the accurate Monte Carlo (MC) method. In addition, the magnetic anisotropy constant has been obtained by means of the law of approach to saturation magnetization (LAS). The experimental and theoretical results are in good agreement with each other and show that the as-synthesized NPs are single domain and approximately non-interacting. The anisotropy constant and size of the NPs increase by increasing the concentration of precursors in the reaction medium. Nanocomposites have been characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Hysteresis loops were investigated at room temperature using a vibrating sample magnetometer (VSM). The crystallite size of single-domain NPs is lower than 20 nm, and the obtained results from FT-IR confirmed the interaction between PVA and the surface of the particles. These approximately non-interacting NPs are useful for magnetic data storage.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Improvement of the Magnetization and Coercivity of La{sub 0.67}Ca{sub 0.33}MnO{sub 3} Induced by Substitution of Nickel for Manganese

La{sub 0.67}Ca{sub 0.33}Mn{sub 1−x}Ni{sub x}O{sub 3} (0 ≤x ≤ 0.3) is synthesized by solid-state reaction at low temperatures, followed by calcination in air. The precursor and its calcined products are characterized by thermogravimetry and differential scanning calorimetry, x-ray powder diffraction, scanning electron microscopy, and vibrating sample magnetometer. A high-crystallized La{sub 0.67}Ca{sub 0.33}Mn{sub 1−x}Ni{sub x}O{sub 3} with an orthorhombic structure is obtained when the precursor is calcined at 900{sup ∘}C in air for 3 h. Crystallite size of La{sub 0.67}Ca{sub 0.33}Mn{sub 1−x}Ni{sub x}O{sub 3} increases with the increase of Ni content, attributed to the decrease of lattice strains of the La{sub 0.67}Ca{sub 0.33}Mn{sub 1−x}Ni{sub x}O{sub 3} with the increase in Ni content. Nickel substitution can markedly improve coercivity and specific magnetization of La{sub 0.67}Ca{sub 0.33}Mn{sub 1−x}Ni{sub x}O{sub 3}. The coercive field (9 Oe) of La{sub 0.67}Ca{sub 0.33}Mn{sub 0.7}Ni{sub 0.3}O{sub 3} is higher, even at 293 K, indicating that La{sub 0.67}Ca{sub 0.33}Mn{sub 0.7}Ni{sub 0.3}O{sub 3} continues being ferromagnetic above 260 K (Curie temperature for LCMO).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Mn Doping on the Structural, Magnetic, and Magnetocaloric Effect of Fe{sub 17}Dy{sub 2} Compounds

Crystal structural and magnetic properties of polycrystalline (Fe{sub 1−x}Mn{sub x}){sub 17}Dy{sub 2} (x = 0.0, 0.1, 0.2, and 0.3) compounds were studied by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) measurements. The results show that (Fe{sub 1−x}Mn{sub x}){sub 17}Dy{sub 2} forms as a substitutional solid solution with the hexagonal Th{sub 2}Ni{sub 17} type. The unit cell volume increases with Mn content. The Curie temperature (T{sub C}) can be tuned from 364 K for x = 0.0 to 80 K for x = 0.3. The magnetic transition at T{sub C} is a typical second-order ferromagnetic-paramagnetic transition. For an applied field change from 0 to 5 T, the maximum magnetic entropy change (| − ΔS{sub M}|) for (Fe{sub 1−x}Mn{sub x}){sub 17}Dy{sub 2} (x = 0.0, 0.1, and 0.2) compounds are 3.9, 2.8, and 1.7 J kg{sup −1} k{sup −1}, respectively. The high ΔS{sub M}, appropriate T{sub C}, and a high performance-to-cost ratio make (Fe{sub 1−x}Mn{sub x}){sub 17}Dy{sub 2} compounds a candidate materials for room-temperature magnetic refrigeration applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural and Magnetic Properties of Thermal- and Deformation-Induced Martensite in an Fe-27%Ni-4%Mn-1%Zn Alloy

Deformation- and thermal-induced martensite properties were examined according to existing martensite morphology and magnetic properties for same prior austenite homogenization conditions in Fe-27%Ni-4%Mn-1%Zn alloy. Scanning electron microscope (SEM) and vibrating sample magnetometer (VSM) characterization techniques were employed for the investigation. Scanning electron microscope observations showed that while martensite formation in the austenite phase of alloy exhibited a lath morphology by thermal effect, elongated deformation-induced martensite morphology exists after deformation. The Curie temperatures were detected at about 201 K for thermal-induced martensite and at about 226 K for deformation-induced martensite from VSM measurements. The magnetic saturation values were determined as about 21 emu g{sup −1} for thermal-induced martensite and 23 emu g{sup −1} for deformation-induced martensite. We found that magnetic saturation increased with deformation effect. On the other hand, VSM offered the soft ferromagnetic characteristic with coersive values of 36 Oe for thermal-induced martensite and the soft ferromagnetic characteristic with 47 Oe for deformation-induced martensite. The changes in the magnetic properties resulting from the thermal and deformation affect were clearly determined. Deformation caused magnetic stabilization in Fe-27%Ni-4%Mn-1%Zn alloy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Development of Broadband Microwave Absorber and Measurement of Its Magnetic and Microwave Properties

Toroid shape Co-doped barium hexaferrites of composition (BaFe{sub 11}CoO{sub 19}) are prepared by standard sintering technology as a sample. In this work, XRD is used to identify the structure of synthesized sample. Vibrating sample magnetometer is used to obtain magnetic hysteresis loop of sample. Scanning electron microscope is used for surface morphology of sample. The complex permeability and permittivity are measured with commercial automation measurement set up in the 2–18 GHz frequency range. As a result of measurement, the calculation of reflection loss of the synthesized samples has been carried out. Investigation of microwave absorption properties revealed that the maximum reflection loss of Co-doped barium hexaferrite sample is around −20 dB and almost flat in the measurement frequency band. From these results, it was concluded that Co-doped barium hexaferrites of composition had a good potential as microwave absorber in the broadband frequency range.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Preparation, Electrical and Magnetic Properties of Poly(m-phenylenediamine)/ZnFe{sub 2}O{sub 4} Nanocomposites

The different ratios of ZnFe{sub 2}O{sub 4} nanoparticles (10 and 20%) were wrapped on poly(m-phenylenediamine) through in situ oxidative polymerization method. The formation of PmPD/ZnFe{sub 2}O{sub 4} nanocomposites was confirmed through FTIR spectroscopy and XRD pattern. From the XRD results, the average crystalline size of ZnFe{sub 2}O{sub 4} nanoparticles and PmPD/ZnFe{sub 2}O{sub 4} nanocomposites were also calculated. The SEM image of ZnFe{sub 2}O{sub 4} nanoparticles shows granular morphology and FESEM images of PmPD/ZnFe{sub 2}O{sub 4} nanocomposites indicate the ZnFe{sub 2}O{sub 4} nanoparticles are agglomerated on PmPD matrix. The soft magnetic behavior of ZnFe{sub 2}O{sub 4} nanoparticles and PmPD/ZnFe{sub 2}O{sub 4} nanocomposites were observed from vibrating sample magnetometer. The dielectric properties of PmPD/ZnFe{sub 2}O{sub 4} nanocomposites were studied with different temperatures and frequencies. The magnetic properties of ZnFe{sub 2}O{sub 4} nanoparticles were also analyzed through Mössbauer spectroscopy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic Responses of Divinylbenzene-Fe{sub 3}O{sub 4} Composite Film Deposited by Free Radical Polymerization Method

The study reports some novel information on both production and characterization for the poly [DVB/Fe{sub 3}O{sub 4}] composite film deposited by free radical polymerization method. The composite film consists of a combination of organic phase and magnetite nanoparticles. The magnetization behavior of the poly [DVB/Fe{sub 3}O{sub 4}] composite film was analyzed with both vibrating sample magnetometers (VSM) and a technique of electron spin resonance (ESR). It was found that the ESR study performed at room temperature showed the poly [DVB/Fe{sub 3}O{sub 4}] composite film had strong transition of g{sub eff} ∼2.5 (254 mT) due to the Fe{sup 3+} S-state ions. This g{sub eff} value indicated that the composite film behavior was near superparamagnetism. The VSM results also supported the ESR results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Influence of Temperature on Sr{sub 0.35}La{sub 0.40}Ca{sub .25}Fe{sub 11.6}Co{sub 0.4}O{sub 19} Hexagonal Ferrites Against Structural, Morphological and Magnetic Properties Prepared by Conventional Ceramic Reaction Methodology

Conventional Ceramic Reaction Methodology has been utilized for the preparation of M-type hexagonal ferrites of Sr{sub 0.35}La{sub 0.40}Ca{sub 0.25}Fe{sub 11.6}Co{sub 0.4}O{sub 19} magnets. X-ray diffraction has been performed for phase determination of the magnetic powders. At calcination temperatures ranging from 1220 to 1330 {sup ∘}C, the synchronize compost of the magnetic powders comprised of M-type hexagonal ferrites together with a small amount of impurity phase such as α-Fe{sub 2}O{sub 3} were co-existed. At calcination temperature above 1270 {sup ∘}C, single-phase M-type hexaferrites can be obtained. The particles seemed to be in a hexagonal plate-like mould which spread-out homogeneously were examined by field emission scanning electron microscopy. The magnetic edibility of the magnetic powders was intended by permanent magnetic measurement test equipment vibrating sample magnetometer. Magnetic properties, such as specific saturation magnetization, coercivity and remanence were temperature-dependent. However, with the increase of sintering temperature, i.e. above 1270 {sup ∘}C, saturation magnetization was increased while the coercivity showed reversed order.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

SPION@APTES@FA-PEG@Usnic Acid Bionanodrug for Cancer Therapy

In this work, we aimed to develop stable usnic acid (UA)-conjugated superparamagnetic iron oxide nanoparticles (SPIONs) as a potential drug carrier for in vitro analysis of MCF-7 (breast cancer cell line), HeLa (cervix cancer cell line), L929 (mouse fibroblast cell line), U87 (glioblastoma cell line, brain cancer), and A549 (human lung cancer cell line) cell lines. SPIONs were synthesized via the polyol method and functionalized with APTES using the Stöber method. Carboxylated polyethylene glycol (PEG-COOH), folic acid (FA), and carboxylated luteolin (CL) were conjugated on the surface via a carboxylic/amine group using the nanoprecipitation method, respectively. X-ray powder diffraction analysis confirmed the purity of the product with crystallite size of around 11 nm. Fourier-transformed infrared spectrophotometer (FT-IR) analyses explained the conjugation of all functional groups to the surface of SPIONs. The percentages of inorganic and organic content in the products were investigated via thermal gravimetric analyzer (TGA). For morphological analysis, a transmission electron microscope (TEM) was used. The superparamagnetic property of the product was also confirmed by vibrating sample magnetometer (VSM).

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Giant Exchange Bias of Hysteresis Loops on Cr{sup 3+}-doped Ag Nanoparticles

In this study, we fabricate Cr-doped Ag nanoparticles (AgCrO{sub 2} and Ag{sub 0.5}Cr{sub 2.5}O{sub 4}) by flash autocombustion method. XRD confirmed that the samples have a single-phase spinel structure. The morphology is studied using high-resolution transmission electron microscopy (HRTEM) to confirm that the samples are on nanoscale. The magnetic properties are studied using a vibrating sample magnetometer (VSM) at room temperature (300 K) and at low temperatures (200 and 100 K). Exchange bias has occurred for the investigated samples below room temperatures. The shifts have occurred in the horizontal directions which may be ascribed to the frozen spins in the samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic and Structural Properties of SrFe{sub 12−x}Cr{sub x}O{sub 19} (x = 0, 0.25, 0.5, 0.75, 1) Hexaferrite Powders Obtained by Sol–Gel Auto-Combustion Method

The crystalline structure and magnetic properties of chromium substituted hexagonal strontium ferrite, SrFe{sub 12−x}Cr{sub x}O{sub 19} (x = 0, 0.25, 0.5, 0.75, 1), nanoparticles have been investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometer (VSM). These materials were prepared by the chemical sol–gel auto-combustion method. From the structural analysis, it was observed that the non-magnetic phase α-Fe{sub 2}O{sub 3} appears after x ≥ 0.5 and remains to be a hexagonal magnetoplumbite phase for x < 0.5. Various parameters such as lattice constants (a and c) were calculated from the XRD data. The coercively H{sub c} initially decreases and then increases with increasing chromium concentration. The saturation magnetization exhibits an increase as the chromium content increases up to (x = 0.25) and then decreases with increase in the Cr content ion from 75.19 to 61.66 emu/g due to the substitution of Fe{sup 3+} ions by less magnetic Cr{sup 3+} ions. Furthermore, M{sub r} continually decreases with increase in the Cr content.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Transition of Magnetic Characteristics from Paramagnetic State to Ferromagnetic Phase in Ce{sub 1−x}Ni{sub x}O{sub 2} Nanoparticles

Nowadays, oxide-based diluted magnetic semiconductor nanoparticles are the most reliable compounds, wherein they accommodate both spin as well as charge of the electron in single domain, means most preferable for the fabrication of spintronic devices. In this view, we report on new Ce{sub 1−x}Ni{sub x}O{sub 2} (x = 0.00, 0.02, 0.04, 0.06, and 0.08) nanoparticles prepared by precipitation method via polyethylene glycol as a surfactant. XRD analysis revealed that all the synthesized nanoparticles were crystallized in distinct FCC fluorite structure as that of CeO{sub 2} host lattice. Transmission electron microscopy analysis confirmed that all the synthesized samples were in spherical shape with average particle size of 8–10 nm, which is well concord with the grain size estimated from the Scherrer formula. The vibrating sample magnetometer evaluations suggested that pristine host lattice shows signals of paramagnetism; meanwhile, Ni substitution CeO{sub 2} nanoparticles exhibits strong ferromagnetism at room temperature. Particularly, 4% Ni-doped CeO{sub 2} samples shows enhanced ferromagnetism and which is suppressed with raising dopant concentration. The perceived magnetization with respect to the Ni dopant concentration is well anticipated by F-center exchange mechanism. We expect that the observations in this research suggest suitable path for preparing of various oxide-based diluted magnetic semiconductor nanoparticles and their applications in fabrication of spintronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electrochemical and Magnetic Properties of Electrospun SrTi{sub 1−x}Fe{sub x}O{sub 3} (x = 0, 0.05 and 0.10) Nanofibers for Anodes of Li-Ion Batteries

SrTi{sub 1−x}Fe{sub x}O{sub 3} (x = 0, 0.05 and 0.1) nanofibers (NFs) were fabricated by electrospinning technique. As prepared products were calcined at 800 {sup ∘} C in argon atmosphere for 3 h to obtain a perovskite phase. The crystal structure and morphology of samples were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Electrochemical and magnetic properties of calcined NFs were studied using a potentiostat/galvanostat electrochemical cell system and vibrating sample magnetometer (VSM), respectively. XRD results showed the cubic perovskite structure of calcined samples with the diameter estimated by TEM in the range of 137.4–141.3 nm SEM micrographs revealed the linkage of crystalline grains in NFs of porous and rough surfaces. Electrochemical properties performed on coin-cell-type Li-ion batteries (LIBs) with calcined SrTi{sub 1−x}Fe{sub x}O{sub 3} (x = 0.05 and 0.10) NF-based anodes showed a significant increase of the specific capacity from 305 to 431 mAh/g for the first cycle with the reversible values of 100 and 130 mAh/g, respectively. VSM measurements at room temperature (RT) indicated that calcined SrTiO{sub 3} NFs exhibited paramagnetic (PM) behavior, while calcined SrTi{sub 1−x}Fe{sub x}O{sub 3} NFs displayed ferromagnetic (FM) behavior at RT with the increase of unsaturated magnetization at 10 kOe from 0.46 to 0.82 emu/g for samples with x = 0.05 and 0.10, respectively. The observed FM behavior in calcined SrTi{sub 1−x}Fe{sub x}O{sub 3} (x = 0.05 and 0.1) NFs was suggested to originate from the face center exchange (FCE) mechanism owing to Fe{sup 3+} –Vo–Fe{sup 3+} couplings.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Microwave-Hydrothermal Synthesis of Y{sub 3}Fe{sub 5}O{sub 12} Nanoparticles: Sintering Temperature Effect on Structural, Magnetic and Dielectric Properties

Herein, we report a facile microwave-assisted hydrothermal method for the preparation of yttrium iron garnet (YIG, Y{sub 3}Fe{sub 5}O{sub 12})nanocrystals and realized the synergy between its structural and magnetic properties. The as-prepared powder thermal stability was characterized in detail by using thermogravimetric-differential thermal analysis (TG-DTA). The synthesized powder was microwave sintered at six different temperatures ranging from 973 to 1373 K for 60 min and characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Magnetic properties were investigated by vibrating-sample magnetometer (VSM) and ferromagnetic resonance (FMR) studies. The frequency variation of dielectric and magnetic properties was measured in the frequency range of 100 kHz–1.8 GHz. The observed magnetic and dielectric parameters such as saturation magnetization, coercivity, permeability, linewidth, dielectric constant and magnetodielectric losses are strongly affected by sintering temperature. The saturation magnetization and coercivity of YIG were found in the range 14.4–28.0 emu/g and 35–87 Oe, respectively. Furthermore, the FMR linewidth decreases from 844 to 204 Oe. This analysis undoubtedly demonstrates that the synthesis method and sintering temperature have the prominent effect on the electrical and magnetic properties of YIG and would be very useful for the garnet-based microwave device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effects of Nd, Er Doping on the Structure and Magnetic Properties of YFeO{sub 3}

Nd, Er co-doped YFeO{sub 3} compounds were synthesized by sol-gel method. The prepared compounds were characterized by powder x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive x-ray (EDX), and vibrating sample magnetometer (VSM) integrated in a physical property measurement system (PPMS-9), respectively. The results show that the compounds possess orthorhombic perovskite structure. The Y{sub 0.5}Er{sub 0.1}Nd{sub 0.4}FeO{sub 3} compound mainly consists of five elements (Er, Nd, Y, Fe, and O) and atom ratio matched well with the formula. With the increase of Nd{sup 3+} doping content in Y{sub 0.5}Er{sub 0.5−x}Nd{sub x}FeO{sub 3} (x = 0, 0.1, 0.2, 0.3, and 0.4), the coercivity increases gradually while the saturation magnetization and remanent magnetization decrease at the same time. Introducing Nd{sup 3+} and Er{sup 3+} ions into YFeO{sub 3} will make a change on a structure distortion, resulting in the decrease of the Fe–O–Fe angle and the consequent reduction of superexchange effect. From our research results, the relationship between the r (R{sup 3+}) and the superexchange bond angle is different from pure-phase orthoferrites R FeO{sub 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic Performance and Evaluation of Radiofrequency Hyperthermia of Perovskite La{sub 1−x}Sr{sub x}MnO{sub 3}

Magnetic nanoparticles (MNPs) can induce localized hyperthermia by alternating magnetic fields, in order to kill cells at tumor sites. In this study, La{sub 1−x}Sr{sub x}MnO{sub 3} nanoparticles with x = 0.2, 0.3, 0.4, and 0.5 were prepared via sol–gel technique. The synthesized nanoparticles were characterized in terms of structure, morphology, and magnetic properties with Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) studies. The average size of nanoparticles was measured to be 57.09, 30.477, 10.24, and 35.982 nm by Williamson–Hall method for x = 0.2, 0.3, 0.4, and 0.5, respectively. The absence of hysteresis in the magnetic response of nanoparticles represents the superparamagnetic behavior. Toxicity test was also performed to evaluate the toxicity concerns of the prepared nanoparticles upon entrance to the body. Furthermore, the alternating current magnetic heating characteristics of La{sub 1−x}Sr{sub x}MnO{sub 3} nanoparticles was also studied, by 1 mg/mL concentration, to test the ability of the nanoparticles as magnetic hyperthermia treatment agents. The magnetothermia were measured in an RF magnetic field of 88 Oe and 430 kHz. The present work reveals that LSMO nanoparticles possess the biocompatible properties for biomedical applications and can provide the required heat at appropriate time.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic Behavior of Iron-Rich Permalloy Nanoparticles

Iron-rich permalloy Fe{sub x}Ni{sub 1−x} nanoparticles (NPs) were fabricated using a low-temperature wet chemistry method involving the hydrothermal growth of the NPs. Three Fe–Ni NPs (Fe{sub 0.5}Ni{sub 0.5}, Fe{sub 0.625}Ni{sub 0.375}, and Fe{sub 0.83}Ni{sub 0.17}) were fabricated and studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). After the initial formations, the three Fe–Ni NPs were annealed at 200, 400, and 600 °C; the XRD showed that all three FeNi NPs had a bcc structure (not the fcc structure of the standard Fe{sub 20}Ni{sub 80} permalloy). The SEM images showed that the NPs had spherical shapes. The VSM measurements showed that none of the Fe–Ni nanoparticles were superparamagnets but were ferromagnets. The heat treatments cause the work needed to the flip the spin (coercivity (H{sub c})) to increase and the values of the saturation magnetizations to fluctuate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗