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21.
Low‐field magnetoresistance is an effective and energy‐saving way to use half‐metallic materials in magnetic reading heads and magnetic random access memory. Common spin‐polarized materials with low field magnetoresistance effect are perovskite‐type manganese, cobalt, and molybdenum oxides. In this study, we report a new type of spinel cobaltite materials, self‐assembled nanocrystalline NiCo2O4, which shows large low field magnetoresistance as large as –19.1% at 0.5 T and –50% at 9 T (2 K). The large low field magnetoresistance is attributed to the fast magnetization rotation of the core nanocrystals. The surface spin‐glass is responsible for the observed weak saturation of magnetoresistance under high fields. Our calculation demonstrates that the half‐metallicity of NiCo2O4 comes from the hopping eg electrons within the tetrahedral Co‐atoms and the octahedral Ni‐atoms. The discovery of large low‐field magnetoresistance in simple spinel oxide NiCo2O4, a non‐perovskite oxide, leads to an extended family of low‐field magnetoresistance materials. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
22.
Imaging the Magnetic Reversal of Isolated and Organized Molecular‐Based Nanoparticles using Magnetic Force Microscopy 下载免费PDF全文
Elena Pinilla‐Cienfuegos Samuel Mañas‐Valero Josep Canet‐Ferrer Laure Catala Talal Mallah Alicia Forment‐Aliaga Eugenio Coronado 《Particle & Particle Systems Characterization》2015,32(6):693-700
In the race towards miniaturization in nanoelectronics, magnetic nanoparticles (MNPs) have emerged as potential candidates for their integration in ultrahigh‐density recording media. Molecular‐based materials open the possibility to design new tailor‐made MNPs with variable composition and sizes, which benefit from the intrinsic properties of these materials. Before their implementation in real devices is reached, a precise organization on surfaces and a reliable characterization and manipulation of their individual magnetic behavior are required. In this paper, it is demonstrated how molecular‐based MNPs are accurately organized on surfaces and how the magnetic properties of the individual MNPs are detected and tuned by means of low‐temperature magnetic force microscopy (LT‐MFM) with variable magnetic field. The magnetization reversal on isolated and organized MNPs is investigated; in addition, the temperature dependence of their magnetic response is evaluated. 相似文献
23.
第一过渡系中的顺磁性离子CrⅢ、MnⅡ/MnⅢ、FeⅡ/FeⅢ、CoⅡ、NiⅡ和CuⅡ及抗磁性离子CoⅢ和ZnⅡ均可与DyⅢ在多齿螯合配体配位下形成单分子磁体配合物。在本文中,我们阐述或汇总了几乎所有的第一过渡系金属-镝单分子磁体。对于由顺磁性第一过渡金属离子和DyⅢ离子形成的配合物,有2个有趣的现象需要引起人们的注意:一是一些Cr-Dy配合物具有较高的阻塞温度和较大的矫顽场,这可归功于配合物内CrⅢ离子和DyⅢ离子之间较强的磁耦合作用(|J|>10 cm-1)。二是报道的FeⅡ2-Dy配合物的能垒可达到319 cm-1(459 K),这在第一过渡系金属-镝单分子磁体中也是比较高的。这可能与FeⅡ2-Dy中DyⅢ具有较高的轴向对称性(D5h)有关,且从头计算表明该配合物中Dy的第一激发态也具有较高的轴向对称性。除了部分Cr-Dy和FeⅡ-Dy配合物外,其他顺磁性第一过渡金属-Dy的能垒较低,这可能由配合物内顺磁离子间弱的磁耦合造成的。为了消除磁耦合对磁弛豫行为影响,近年来人们关注于使用抗磁性第一过渡金属离子与DyⅢ构建单分子磁体配合物。相比其他核数的Zn-Dy配合物,三核Zn2Dy配合物被报道的数目最多且研究得最为深入,这可能与较易调控Zn2Dy中Dy配位几何对称性有关。最后,我们提出了几点关于进一步提升第一过渡系金属-镝单分子磁体的磁性能的建议,其中最为重要的是控制Dy配位几何的轴向对称性及Dy的基态mJ的电荷分布。对于第一过渡系金属-镝单分子磁体中的DyⅢ离子,DyⅢ基态mJ的电荷与配体的电荷之间的静电排斥应该降到最低。 相似文献
24.
L.H. KongY.L. Gao T.T. SongQ.J. Zhai 《Journal of magnetism and magnetic materials》2011,323(16):2165-2169
Structure and magnetic properties of Nb-doped (FeZrB)100−xNbx alloy are investigated by X-ray diffraction (XRD), differential scanning calorimetry and vibrating sample magnetometer. The fully amorphous structure of the as-quenched ribbons is confirmed by the XRD pattern. With increasing Nb, the glass transition temperature and the onset crystallization temperature are increased, indicating increased stability of the amorphous structure. For x=1, the saturation magnetization of the ribbons is 125.7 emu/g and the optimized annealing temperature increases from 550 to 630 °C. The morphology of the crystallized phases is observed by scanning electron microscopy. The results show that nanocrystalline α-Fe grains are dispersed in the amorphous matrix. 相似文献
25.
V. I. Trukhin V. I. Maksimochkin Yu. A. Minina 《Moscow University Physics Bulletin》2009,64(3):344-348
The behavior of two-sublattice natural ferromagnetics under the effects of static and variable fields and high and low temperatures
is studied. Novel unknown peculiarities of thermoremanent magnetization (TRM) and partial thermoremanent magnetization (pTRM)
dependences on fields and temperatures are obtained. Self-reversal of TM and pTRM in the sample, where self-reversal has not
been observed prior to the application of fields and temperatures, is revealed.
Original Russian Text ? V.I. Trukhin, V.I. Maksimochkin, Yu.A. Minina, 2009, published in Vestnik Moskovskogo Universiteta.
Fizika, 2009, No. 3, pp. 103–107. 相似文献
26.
Sadhan Ghosh 《Journal of magnetism and magnetic materials》2011,323(5):552-556
This work reports isothermal reversible variation of magnetization in nanoporous Pd-Ni alloys subjected to continuous charging and discharging of the sample in aprotic electrolyte medium. Polarizing metal surface with excess charge also finds strain in the nanoporous structure using the sample as working electrode. Therefore, it is proposed that pressure induced by strain is the key parameter for the observed reversible magnetization in the transition metal alloys. 相似文献
27.
A. Adanlété AdjanohR. Belhi J. VogelM. Ayadi K. Abdelmoula 《Journal of magnetism and magnetic materials》2011,323(5):504-508
Magnetization reversal in ultra-thin Au/Co/Au films deposited on single crystal silicon (1 0 0) was investigated using Kerr microscopy. In the considered ultra-thin Co films, with a thickness between 0.7 and 1 nm, the coercivity and magnetic anisotropy decrease with decrease in cobalt layer thickness and the magnetization reversal dynamics is dominated by disordered domain wall motion. An analysis of the observed magnetization reversal dynamics is proposed, starting from the Fatuzzo-Labrune model. We show that the relaxation curves of these samples are well described by a function obtained by a technical transformation of Fatuzzo-Labrune model in the regime dominated by domain wall motion. 相似文献
28.
Theoretical analysis of the anisotropy of the magnetization of the Ho^3+ ion in holmium iron garnet single crystals 下载免费PDF全文
The spontaneous magnetization of the Ho^3+ ion in holmium iron garnet (HoIG) single crystals in the temperature range of 4.2-294K along the directions [111], [110], and [100] are calculated, taking into account the effects of six magnetically inequivalent sites occupied by the Ho^3+ ions based on the quantum theory. The calculated results show that the magnetization of the Ho^3+ ion in HoIG is obviously anisotropic. The theoretical results ave in agreement with those of experiments. A primary interpretation of the anisotropy of magnetization of the Ho^3+ ion in HoIG is put forward. 相似文献
29.
Low-field microwave absorption has been measured as a function of magnetic field in a series of thin film structures exhibiting or not exhibiting the giant magnetoresistance effect (GMR). Although a close correlation has been found between the microwave absorption and GMR, an additional absorption due to magnetization reversal is shown to have substantial effect on the overall microwave response. 相似文献
30.
Magnetic and transport properties of Tm2Co7B3 compound have been studied. This compound crystallizes in the hexagonal Ce2Co7B3 type structure. The coercivity (H
c) of the compound was determined from hysteresis measurements in fields up to 4 T. The temperature dependence of coercivity has been explained by a thermally activated process of domain wall motion. The resistivity at low temperatures shows a T
2 dependence. At higher temperatures the resistivity is not a linear function of temperature, which indicates an electron-phonon interaction in the presence of a small s-d scattering. 相似文献