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1.
We present the synthesis, microstructural and magnetic characterization of cubic CoO nanoparticles with well-controlled size and shape. The as-synthesized CoO nanoparticles are stable because of the organic coating that occurred in situ. The Néel temperature is 225 and 280 K for the 42 and 74 nm CoO particles, respectively. The CoO nanoparticles exhibit anomalous magnetic properties, such as large moments, coercivities and loop shifts. These results provide evidence for the formation of spin compensated random system in CoO. The structurally distorted and magnetically disordered surface layer ferromagnetic phase played an important role in the magnetic behavior of CoO nanoparticles. The smaller is the particle size, the stronger is the contribution of the ferromagnetic phase and the more is the surface layer helpful to enhance the observed coercivity and the exchange bias. 相似文献
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Magnetic properties of CoO nanoparticles 总被引:2,自引:0,他引:2
《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,9(1-4):479-481
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《Photonics and Nanostructures》2014,12(2):144-151
Magnetic properties of magnetophotonic crystals based on opal matrices have been studied as well as their electromagnetic properties in millimeter waveband. The particles of cobalt oxide are embedded into the inter-sphere voids of the matrix. After annealing in hydrogen the cobalt oxide particles transform to metallic cobalt. It has been shown that if antiferromagnetic cobalt oxide remains besides ferromagnetic cobalt, the low-temperature magnetic hysteresis loop is shifted along the field axis. Magnetic field influences essentially on the microwave transmission and reflection coefficients only after annealing in hydrogen that is if the ferromagnetic phase presents in the sample. The spectra of magnetic resonance and antiresonance are studied. 相似文献
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Uniform iron oxide nanoparticles in the size range from 10 to 24 nm and polydisperse 14 nm iron oxide particles were prepared by thermal decomposition of Fe(III) carboxylates in the presence of oleic acid and co-precipitation of Fe(II) and Fe(III) chlorides by ammonium hydroxide followed by oxidation, respectively. While the first method produced hydrophobic oleic acid coated particles, the second one formed hydrophilic, but uncoated, nanoparticles. To make the iron oxide particles water dispersible and colloidally stable, their surface was modified with poly(ethylene glycol) and sucrose, respectively. Size and size distribution of the nanoparticles was determined by transmission electron microscopy, dynamic light scattering and X-ray diffraction. Surface of the PEG-functionalized and sucrose-modified iron oxide particles was characterized by Fourier transform infrared (FT-IR) and Raman spectroscopy and thermogravimetric analysis (TGA). Magnetic properties were measured by means of vibration sample magnetometry and specific absorption rate in alternating magnetic fields was determined calorimetrically. It was found, that larger ferrimagnetic particles showed higher heating performance than smaller superparamagnetic ones. In the transition range between superparamagnetism and ferrimagnetism, samples with a broader size distribution provided higher heating power than narrow size distributed particles of comparable mean size. Here presented particles showed promising properties for a possible application in magnetic hyperthermia. 相似文献
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S.M. Zhou D. Imhoff K. Yu-Zhang Y. Leprince-Wang 《Applied Physics A: Materials Science & Processing》2005,81(1):115-118
In CoO-Ag granular films with small CoO contents, we have observed ultrafine Co particles inside or on the surface of the CoO particles. After field cooling under the external magnetic field of 50 kOe, a sustained magnetization (or vertical) shift and exchange field shift were observed. The magnetization shift and the exchange field shift increased as the cooling field is increased and temperature decreased, in correlation to each other. PACS 75.30.Et; 75.30.Gw; 75.75.+a 相似文献
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M. Ijjaali K. Kowalski T. Bak B. Dupre C. Gleitzer J. Nowotny M. Rekas C. C. Sorrell 《Ionics》2001,7(4-6):351-359
This paper reports the results of the electrical conductivity measurements for polycrystalline specimens of undoped and Cr-doped
CoO in the ranges of p(O2) (10−5 – 105 Pa) and temperature (1223 – 1373 K). The experimental data are considered in terms of the effect of Cr on semiconducting
properties of CoO. It is shown that Cr results in a decrease of the reciprocal of the p(O2) exponent of electrical conductivity, however, the obtained experimental values are substantially lower than those predicted
by defect chemistry. The activation energy of the electrical conductivity remains independent of p(O2) and Cr content (at the level of about 0.5 eV) except strongly reduced CoO, at p(O2)=2.10−4 Pa, of which the activation energy is substantially higher. Thermopowervs p(O2) exhibits maximum at p(O2)=10 Pa (except of thermopower data for Cr-doped CoO at the highest temperature). The experimental data are considered in
terms of the effect of both p(O2) and Cr on semiconducting properties. 相似文献
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《Solid State Ionics》1987,24(3):217-223
Seebeck coefficient and electrical conductivity have been measured at 1270–1470 K versus oxygen partial pressure from 102 and 105 Pa. An increase of the Fermi energy and a decrease of electrical conductivity of CoO versus In concentration have been observed within the In solubility range (below 1 mol%). The application of the Debye-Hückel theory for strong electrolytes explains the oxygen partial pressure dependence of both electrical conductivity and Seebeck coefficient. 相似文献
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We use Monte Carlo simulations to study the influence of dipolar interaction on the equilibrium magnetic properties of monodisperse single-domain ferromagnetic nanoparticles. Low field magnetizations simulated in zero field cooling (ZFC)/field cooling (FC) procedures and field-dependent magnetization curves above the blocking temperatures show strong dependence on the concentration and the spatial arrangement (cubic or random) of the magnetic particles. The field-dependent magnetizations can not be simply described by the T* model at relative low temperatures due to the interplay between anisotropy and dipolar interactions, as well as the spatial arrangement effect. 相似文献
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F. Tournus N. Blanc A. Tamion M. Hillenkamp V. Dupuis 《Journal of magnetism and magnetic materials》2011,323(14):1868-1872
CoPt nanoparticles are widely studied, in particular for their potentially very high magnetic anisotropy. However, their magnetic properties can differ from the bulk ones and they are expected to vary with the particle size. In this paper, we report the synthesis and characterization of well-defined CoPt nanoparticle samples produced in ultrahigh vacuum conditions following a physical route: the mass-selected low energy cluster beam deposition technique. This approach relies on an electrostatic deviation of ionized clusters which allows us to easily adjust the particle size, independently from the deposited equivalent thickness (i.e. the surface or volume particle density in a sample). Diluted samples made of CoPt particles, with different diameters, embedded in amorphous carbon are studied by transmission electron microscopy and superconducting interference device magnetometry, which gives access to the magnetic anisotropy energy distribution. We then compare the magnetic properties of two different particle sizes. The results are found to be consistent with an anisotropy constant (including its distribution) which does not evolve with the particle size in the range considered. 相似文献
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Yuanqing He Yudhisthira Sahoo Shumin Wang Hong Luo Paras N. Prasad Mark T. Swihart 《Journal of nanoparticle research》2006,8(3-4):335-342
Nanoparticles of iron have been prepared by laser-driven decomposition of iron pentacarbonyl vapor. In this method, an infrared laser rapidly heats a dilute mixture of precursor vapors to decompose the precursor and initiate particle nucleation. It was found that when using SF6 as a photosensitizer during the synthesis, ferrous fluoride (FeF2) was produced as an undesired byproduct in the product powder. The particle size, composition, and crystalline structure have been characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS). Results of magnetization measurements for small iron nanoparticles (about 5 nm diameter) are also presented, showing superparamagnetic behavior at room temperature, and a blocking temperature near 125 K. 相似文献
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The structure and the magnetic properties of the doped rare earth cobaltite systems are of recent interest owing to the CMR
phenomenon that occur in them. In this paper, we investigate the structure and magnetic properties of Tb0.5Sr0.5CoO3 solid solution, for the first time, using neutron powder diffraction technique. The sample Tb0.5Sr0.5CoO3 is found to crystallize in orthorhombic (Pbnm) symmetry. The unit cell volume and Co—O bond length reduce with temperature.
The calculatede
g bandwidth obtained from structural parameters turns out to be 0.989 eV. Low temperature neutron diffraction profiles exhibit
a magnetic contribution to the fundamental Bragg peaks indicating a ferromagnetic ordering belowT
c. The results are compared with Co—O—Co bond angles and Co—O bond length of La0.5Sr0.5CoO3, highlighting the ionic size effects on substitution of Tb ion for La in the compound. 相似文献
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Magnetic susceptibility χ of several CoO samples has been measured in the temperature range of 4.2–350 K. Below about 140 K, and additional contribution to χ, different for different samples, is observed. It is proposed that this excess susceptibility is due to an uncompensated moment resulting from deviations from stoichimetry. The estimated χ values for a stoichiometric CoO at TN and absolute zero agree with Tachiki's calculations. 相似文献
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K. Kowalski M. Ijjaali T. Bak B. Dupre Ch. Gleitzer J. Nowotny M. Rekas C. C. Sorrell 《Ionics》2001,7(4-6):394-399
This paper reports electrical properties of CoO thin films of different thickness in the range 0.375 – 7.95 μm. Both electrical
conductivity and thermopower were measured at elevated temperatures (1223 – 1423 K) and under controlled oxygen partial pressure
(5 − 2.1x104 Pa). It was found that at low p(O2) the electrical conductivity decreases with film thickness. The activation energy of the electrical conductivity (Ea) in air decreases with the oxide thickness from 0.56 eV at 0.375 μm to 0.52 eV for massive CoO while at low p(O2)=5 Pa the Ea is independent of the thickness (Ea = 0.46 eV). The reciprocal of the p(O2) exponent of the electrical conductivity (nδ) in the range 1223 K – 1373 K is close to four for the 7,95 μm film and is about 3.5–3.7 for the 0.375 μm film. The electrical
properties of the CoO thin films are considered assuming different defect structures in the bulk phase and the surface layer. 相似文献
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Particle size effect on phase and magnetic properties of polymer-coated magnetic nanoparticles 总被引:1,自引:0,他引:1
Srinivasan Balakrishnan Michael J. Bonder George C. Hadjipanayis 《Journal of magnetism and magnetic materials》2009,321(2):117-122
Polymer-coated magnetic nanoparticles are hi-tech materials with ample applications in the field of biomedicine for the treatment of cancer and targeted drug delivery. In this study, magnetic nanoparticles were synthesized by chemical reduction of FeCl2 solution with sodium borohydride and coated with amine-terminated polyethylene glycol (aPEG). By varying the concentration of the reactants, the particle size and the crystallinity of the particles were varied. The particle size was found to increase from 6 to 20 nm and the structure becomes amorphous-like with increase in the molar concentration of the reactant. The magnetization at 1 T field (M1T) for all samples is > 45 emu/g while the coercivity is in the range of 100-350 Oe. When the ethanol-suspended particles are subjected to an alternating magnetic field of 4 Oe at 500 kHz, the temperature is increased to a maximum normalized temperature (3.8 °C/mg) with decreasing particle size. 相似文献
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Inderhees SE Borchers JA Green KS Kim MS Sun K Strycker GL Aronson MC 《Physical review letters》2008,101(11):117202
We present an experimental study of the effects of oxidation on the magnetic and crystal structures of exchange biased epsilon-Co/CoO core-shell nanoparticles. Transmission electron microscopy measurements reveal that oxidation creates a Co-CoO interface which is highly directional and epitaxial in quality. Neutron diffraction measurements find that below a Néel temperature TN of approximately 235 K the magnetization of the CoO shell is modulated by two wave vectors, q1=(1/2 1/2 1/2)2pi/a and q2=(100)2pi/a. Oxidation affects the q1 component of the magnetization very little, but hugely enhances the q2 component, resulting in the magnetic decompensation of the core-shell interface. We propose that the large exchange bias effect results from the highly ordered interface between the Co core and CoO shell, and from enhanced core-shell coupling by the uncompensated interface moment. 相似文献
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The Fe/Cu nanocomposites with iron as core and copper as shell have been successfully synthesized by a two-step reduction method. A spherical nanoparticle of γ-Fe was first fabricated by the reduction of ferrous chloride, and then the Fe particle was coated by nanocrystalline Cu through the reduction of copper sulfate. The thickness of copper shell has been tuned by varying the initial concentration of copper sulfate. The morphology, crystalline structure, chemical composition and magnetic properties of the products were investigated by using transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and vibrating sample magnetometer (VSM). It was found that the saturation magnetization (Ms) values of the Fe/Cu core–shell particles are varied owing to the different thickness of copper layer. Though the Ms value of the Fe/Cu nanocomposite is lower than that of pure iron nanoparticles, the higher Ms value (22.411 emu/g) of the Fe/Cu composites is also investigated. The result of the thermogravimetric analysis (TGA) showed the enhanced antioxidation capacity of the Fe/Cu nanocomposites. This kind of nanocomposites combined the excellent magnetism of iron and the electronic, thermal conductivity of copper, suggesting potential application as a novel electromagnetic material. 相似文献
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Ni nanoparticles (Ni-NPs), with diameter (D) ranging 5–30 nm, were synthesized by reducing nickel chloride with NaBH4 in the presence of polymer molecules of poly-vinyl alcohol (PVA) in cold water. Nickel chloride was dispersed in the PVA molecules which stabilized the resulting Ni-NPs. Experiments were carried out with and without PVA to elucidate the effect of PVA molecules on the structural and magnetic properties of Ni-NPs. It was found that both uncoated (uc) and PVA-coated (pc) Ni-NPs exhibit a tetragonal (t) crystal structure, i.e. different from the cubic (fcc) structure of bulk nickel. pc Ni-NPs (paramagnetic in nature) converted to fcc Ni (spherical shape, D ~ 12 nm) on annealing at 573 K in air, exhibiting a saturation magnetization M s = 20.5 emu/g, squareness ratio M r /M s = 0.48 and coercivity H c = 248 Oe, which is higher than the bulk Ni (0.7 Oe). uc Ni-NPs showed little improvement in M s and H c on air annealing. The core–shell structure resulted in a high H c value in stable pc Ni-NPs in air. Electron magnetic resonance revealed exchange interaction between the core and shell, which changes on annealing in air. 相似文献
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Compared with the top-down lithographic techniques, bottom-up chemical synthesis and self-assembly approaches offer much more flexibilities in creating magnetic nanostructures with controlled size, shape, composition and physical properties. This review summarizes some of the latest developments in this field, with emphasis mainly on transition metals, their alloys and metal oxide nanoparticles. The focus is directed towards the conditions of individual particles as well as large assemblies of particles through colloidal chemistry. Furthermore, some of the future directions in nanomagnetism from the perspective of physical chemists is also presented. 相似文献