共查询到20条相似文献，搜索用时 46 毫秒
1.
The discrepancy between the magnetic hysteresis properties of magnetite crystals that are precipitated from solution (<0.3 micrometer) and of crushed sifted grains (>0.3 micrometer) is not an inherent property of magnetite but is caused by the highly stressed state of crushed material and by adhering finer fragments. The size trends of magnetic properties exhibited by submicrometer-size precipitated grains continue in the size range from 1 micrometer to 1 millimeter in a set of hydrothermally recrystallized magnetite crystals. Coercive forces of these narrowly sized crystals follow a power law over a wide size range (0.1 micrometer to 1 millimeter) as predicted by theory. Dislocation etch pits show similar dislocation densities for hydrothermally grown (3 x 10(10) meter (-2)) and natural (1 x 10(10) meter(-2)) magnetite crystals. Hysteresis parameters of hydrothermally grown crystals are similar to those of natural crystals but are about one-fifth of those for crushed grains. 相似文献
2.
Although magnetic data are the primary evidence for ocean floor spreading, the processes by which magnetic phases in ocean floor basalts are formed remain poorly constrained. Scanning transmission electron microscopic observations show that magnetic single-domain magnetite in sheeted dike basalts of Deep Sea Drilling Project hole 504B formed through oxidation-exsolution of ilmenite, exsolution of ulv?spinel lamellae, and recrystallization of end-member magnetite by interaction with convecting fluids. The data suggest that the sheeted dike basalts, with single-domain magnetite as an efficient and stable magnetic carrier, contribute significantly to sea-floor magnetism. 相似文献
3.
Karato S 《Science (New York, N.Y.)》1993,262(5140):1708-1711
Anisotropy of the inner core of the Earth is proposed to result from the lattice preferred orientation of anisotropic iron crystals during their solidification in the presence of a magnetic field. The resultant seismic anisotropy is related to the geometry of the magnetic field in the core. This hypothesis implies that the observed anisotropy (fast velocity along the rotation axis) indicates a strong toroidal field in the core, which supports a strong field model for the geodynamo if the inner core is made of hexagonal close-packed iron. 相似文献
4.
Magnetoreception by honeybees (Apis mellifera) is demonstrated by such activities as comb building and homing orientation, which are affected by the geomagnetic field. In other magnetoreceptive species, iron oxide crystals in the form of magnetite have been shown to be necessary for primary detection of magnetic fields. Here it is shown that trophocytes, which are apparently the only iron granule-containing cells in honeybees, contain super-paramagnetic magnetite. These cells are innervated by the nervous system, which suggests that trophocytes might be primarily responsible for magnetoreception. Electron microscopy also shows cytoskeletal attachments to the iron granule membrane. 相似文献
5.
Single-domain magnetite crystals have been isolated and characterized from tissue located in a sinus within the dermethmoid bone of the skull of the yellowfin tuna, Thunnus albacares. Their chemical composition, narrow size distribution, and distinctive crystal morphology indicate that these crystals are biochemical precipitates. Experiments on the interaction between particles reveal the organization of the particles in situ and suggest a possible form for candidate magnetoreceptor organelles. The consistent localization of such particles with similar arrangement within the dermethmoids of this and other pelagic fishes suggests that the ethmoid region is a possible location for a vertebrate magnetic sense organ. 相似文献
6.
Jedwab J Herbosch A Wollast R Naessens G Van Geen-Peers N 《Science (New York, N.Y.)》1970,167(3918):618-619
Magnetite crystals larger than 2 micrometers are absent from rocks and fines. Smaller opaque spheres in the fines can tentatively be identified as magnetite. Their concentration is not higher than 1 x 10(-6) particle per particle smaller than 1 millimeter. In the fines from the sampling site, the contribution of material similar to type 1 carbonaceous meteorites is insignificant, either because it never existed, or because it was evaporated or comminuted by impact or was diluted by indigenous material. Other magnetite habits typical of carbonaceous meteorites or possibly of cosmic dust or comets were also sought without success-such as rods, platelets, framboids, spherulites, and idiomorphic crystals. 相似文献
7.
氧化亚铁硫杆菌,通过氧化二价铁或还原态无机硫化物获得能量,在细胞内能合成磁性纳米颗粒。通过扫描电镜和透射电镜对氧化亚铁硫杆菌菌体进行分析。探讨了该菌的趋磁性以及不同铁源对菌体生长和磁小体合成的影响。结果表明:生长于9K培养基的细菌能够合成磁小体,单个细胞的磁小体数目大概为2个;干燥菌体和湿菌体都能被磁铁吸附;当有外加磁场时,细菌在半固体平板和光学显微镜下均可见趋磁性;氧化亚铁硫杆菌生长和磁小体合成的最佳铁源均为硫酸亚铁。 相似文献
8.
Okazaki R Shibauchi T Shi HJ Haga Y Matsuda TD Yamamoto E Onuki Y Ikeda H Matsuda Y 《Science (New York, N.Y.)》2011,331(6016):439-442
A second-order phase transition is characterized by spontaneous symmetry breaking. The nature of the broken symmetry in the so-called "hidden-order" phase transition in the heavy-fermion compound URu(2)Si(2), at transition temperature T(h) = 17.5 K, has posed a long-standing mystery. We report the emergence of an in-plane anisotropy of the magnetic susceptibility below T(h), which breaks the four-fold rotational symmetry of the tetragonal URu(2)Si(2). Two-fold oscillations in the magnetic torque under in-plane field rotation were sensitively detected in small pure crystals. Our findings suggest that the hidden-order phase is an electronic "nematic" phase, a translationally invariant metallic phase with spontaneous breaking of rotational symmetry. 相似文献
9.
[目的]研究双过渡金属-类金属的三元合金纳米线各成分的改变对磁学性质的影响。[方法]在氧化铝模板中用电化学沉积法制备2种体系的Fe-Co-P三元合金纳米线。[结果]用扫描电子显微镜和透射电子显微镜观测氧化铝模板和纳米线的形貌。选区电子衍射和X射线衍射结果表明,(Fe1-xCox)0.88P0.12纳米线为非晶结构,而(Fe1-xCox)0.92P0.08纳米线近似为晶态结构。用振动样品磁强计和穆斯堡尔谱仪研究了非晶态体系和晶态体系在室温下的宏观和微观磁性。随Co含量x的变化,每个体系磁参量的变化趋势基本相似,而当x相同时两体系的磁学性质又有所不同。[结论]纳米线中非晶体系的形状各向异性比晶态更明显,更适宜用于垂直磁记录中。 相似文献
10.
趋磁细菌是一类能够沿着磁场方向运动的革兰氏阴性细菌的总称,其最显著的特征是能够在胞内合成特殊的原核细胞器——磁小体。磁小体是具有外膜包被、纳米级、在胞内成链状排列的Fe3O4或Fe3S4磁性颗粒,并且具有专属的形态、大小和排列。正是因为磁小体的这些特性使不同领域的科研工作者开发着趋磁细菌的应用。另外,磁小体可以作为生物矿化和原核生物形成膜细胞器的理想模型。趋磁细菌磁小体合成相关蛋白在磁小体囊泡的形成、铁的转运、成晶的控制以及胞内磁性颗粒的排列等过程中发挥作用。文中重点介绍了近年来发现的和趋磁细菌磁小体合成相关的蛋白,并对未来磁小体蛋白的研究进行了展望。 相似文献
11.
《Science (New York, N.Y.)》1984,226(4671):116
In the report "A candidate magnetic sense organ in the yellowfin tuna, Thunnus albacares" by M. M. Walker et al. (18 May, p. 751), the standard error given on page 752 (3rd column, first full paragraph) for the sizes of the magnetite particles was instead the standard deviation. Use of the term "standard error" implies a far greater variance in the sizes of the particles than actually existed and could lead to the conclusion that the published electron micrograph is not typical but presents a biased sample of the particles. 相似文献
12.
Hinkov V Haug D Fauqué B Bourges P Sidis Y Ivanov A Bernhard C Lin CT Keimer B 《Science (New York, N.Y.)》2008,319(5863):597-600
Electronic phases with symmetry properties matching those of conventional liquid crystals have recently been discovered in transport experiments on semiconductor heterostructures and metal oxides at millikelvin temperatures. We report the spontaneous onset of a one-dimensional, incommensurate modulation of the spin system in the high-transition-temperature superconductor YBa2Cu3O6.45 upon cooling below approximately 150 kelvin, whereas static magnetic order is absent above 2 kelvin. The evolution of this modulation with temperature and doping parallels that of the in-plane anisotropy of the resistivity, indicating an electronic nematic phase that is stable over a wide temperature range. The results suggest that soft spin fluctuations are a microscopic route toward electronic liquid crystals and that nematic order can coexist with high-temperature superconductivity in underdoped cuprates. 相似文献
13.
A previously undescribed magnetotactic spirillum isolated from a freshwater swamp was mass cultured in the magnetic as well as the nonmagnetic state in chemically defined culture media. Results of Mossbauer spectroscopic analysis applied to whole cells identifies magnetite as a constituent of these magnetic bacteria. 相似文献
14.
Magnetic anisotropy measurements on single crystals of a series of paramagnetic 8-coordinate lanthanide shift reagent adducts of the type Ln[(CH(3))(3)CCOCHCOC(CH(3))(3)(4-CH(3)C(5)H(1)N)(2) have been made for the following lanthanides: praseodymium, neodymium, samarium, europium, terbium, dysprosium, holmium, erbium, thulium, and ytterbium. The susceptibility tensors are highly anisotropic and nonaxial. Dipolar nuclear magnetic resonance shifts evaluated from the solid-state date are in satisfactory agreement with the solution results. 相似文献
15.
I Chong Z Hiroi M Izumi J Shimoyama Y Nakayama K Kishio T Terashima Y Bando M Takano 《Science (New York, N.Y.)》1997,276(5313):770-773
Critical-current density (Jc) is a parameter of primary importance for potential applications of high-temperature copper oxide superconductors. It is limited principally by the breakdown of zero-resistive current due to thermally activated flux flow at high temperatures and high magnetic fields. One promising method to overcome this limitation is to introduce efficient pinning centers into crystals that can suppress the flux flow. A marked increase in Jc was observed in Bi2Sr2CaCu2O8+delta (Bi-2212) single crystals doped with a large amount of Pb. By electron microscopy, characteristic microstructures were revealed that probably underlie the observed enhancement in Jc: thin (10 to 50 nanometers), platelike domains having a modulation-free structure appeared with spacings of 50 to 100 nanometers along the b axis. 相似文献
16.
Bertelsen P Goetz W Madsen MB Kinch KM Hviid SF Knudsen JM Gunnlaugsson HP Merrison J Nørnberg P Squyres SW Bell JF Herkenhoff KE Gorevan S Yen AS Myrick T Klingelhöfer G Rieder R Gellert R 《Science (New York, N.Y.)》2004,305(5685):827-829
The magnetic properties experiments are designed to help identify the magnetic minerals in the dust and rocks on Mars-and to determine whether liquid water was involved in the formation and alteration of these magnetic minerals. Almost all of the dust particles suspended in the martian atmosphere must contain ferrimagnetic minerals (such as maghemite or magnetite) in an amount of approximately 2% by weight. The most magnetic fraction of the dust appears darker than the average dust. Magnetite was detected in the first two rocks ground by Spirit. 相似文献
17.
18.
Gambardella P Rusponi S Veronese M Dhesi SS Grazioli C Dallmeyer A Cabria I Zeller R Dederichs PH Kern K Carbone C Brune H 《Science (New York, N.Y.)》2003,300(5622):1130-1133
The isotropic magnetic moment of a free atom is shown to develop giant magnetic anisotropy energy due to symmetry reduction at an atomically ordered surface. Single cobalt atoms deposited onto platinum (111) are found to have a magnetic anisotropy energy of 9 millielectron volts per atom arising from the combination of unquenched orbital moments (1.1 Bohr magnetons) and strong spin-orbit coupling induced by the platinum substrate. By assembling cobalt nanoparticles containing up to 40 atoms, the magnetic anisotropy energy is further shown to be dependent on single-atom coordination changes. These results confirm theoretical predictions and are of fundamental value to understanding how magnetic anisotropy develops in finite-sized magnetic particles. 相似文献
19.
Weisheit M Fähler S Marty A Souche Y Poinsignon C Givord D 《Science (New York, N.Y.)》2007,315(5810):349-351
A large electric field at the surface of a ferromagnetic metal is expected to appreciably change its electron density. In particular, the metal's intrinsic magnetic properties, which are commonly regarded as fixed material constants, will be affected. This requires, however, that the surface has a strong influence on the material's properties, as is the case with ultrathin films. We demonstrated that the magnetocrystalline anisotropy of ordered iron-platinum (FePt) and iron-palladium (FePd) intermetallic compounds can be reversibly modified by an applied electric field when immersed in an electrolyte. A voltage change of -0.6 volts on 2-nanometer-thick films altered the coercivity by -4.5 and +1% in FePt and FePd, respectively. The modification of the magnetic parameters was attributed to a change in the number of unpaired d electrons in response to the applied electric field. Our device structure is general and should be applicable for characterization of other thin-film magnetic systems. 相似文献
20.
The magnetization directions of individual monodomain nanoparticles as small as 5 nanometers in diameter are determined using the Foucault method of Lorentz microscopy. A model is developed to explain the images and diffraction patterns of samarium cobalt nanoparticles as a function of the aperture shift direction. Thermally induced changes in the magnetization direction of superparamagnetic magnetite nanoparticles were observed but with a much slower rate than expected, due to surface anisotropy. When the time scale for magnetization reversal is much shorter than the data acquisition time, as in carbon-coated iron cobalt alloy nanoparticles, the images show an average of such thermally induced changes. 相似文献