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91.
92.
M. Patra K. De S. Majumdar S. Giri 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):367-371
We observe the negative shift of the magnetic hysteresis loop at 5 K, while the sample is cooled in external magnetic field
in case of 30% of Fe substitution in LaMnO3. The negative shift and training effect of the hysteresis loops indicate the phenomenon of exchange bias. The cooling field
dependence of the negative shift increases with the cooling field below 7.0 kOe and then, decreases with further increase
of cooling field. The temperature dependence of the negative shift of the hysteresis loops exhibits that the negative shift
decreases sharply with increasing temperature and vanishes above 20 K. Temperature dependence of dc magnetization and ac susceptibility
measurements show a sharp peak (Tp) at 51 K and a shoulder (Tf) around 20 K. The relaxation of magnetization shows the ferromagnetic and glassy magnetic components in the relaxation process,
which is in consistent with the cluster-glass compound. 相似文献
93.
A modified combustion process, namely a mixed fuel process making use of a mixture of two fuels, such as citric acid and glycine
has been developed to prepare nanocrystalline ceria powders. The effect of the mixed fuel and the different fuel to oxidant
ratios on the decomposition characteristics of the gels were investigated by simultaneous thermal analysis experiments. It
was established from various characterization techniques that the ceria powder prepared through the mixed fuel process has
got the optimum powder characteristics, namely, a surface area of 33.33 m2/g and a crystallite size of 14 nm compared to the powders produced through the combustion process using a single fuel like
glycine or citric acid. Such powders when sintered at 1250°C resulted in pellets with densities in the range of 94–96% of
theoretical density. In this paper, we have carried out systematic studies on the sintering of ceria powders prepared by different
approaches. The sintered ceramic from mixed fuel batch, exhibited and retained relative density more than 95% up to 1250°C
and this data clearly underscores the ability of this process in developing ceria ceramics with increased stability against
reduction. 相似文献
94.
J. V. Pinto M. M. Cruz R. C. da Silva N. Franco A. Casaca E. Alves M. Godinho 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(3):253-260
The magnetic and electrical properties of Co-implanted
single crystalline TiO2 rutile are presented. For fluences of
the order of 1017 cm-2 and implantation energy of 150
keV the maximum atomic concentration of cobalt is 13 at% at a depth
of 65 nm from the surface. The as implanted single crystals exhibit
superparamagnetic behaviour attributed to the formation of nanosized
cobalt clusters. After annealing at 1073 K an anisotropic
ferromagnetic behaviour emerges with the easy magnetization axis
lying in the (001) plane of rutile. The ferromagnetic behaviour is
associated with oriented cobalt aggregates. Electrical conductivity
of the implanted samples annealed in vacuum also exhibits
anisotropic behaviour at low temperatures, but no magnetoresistive
effects were detected. 相似文献
95.
The FePt system has important perspectives as high-temperature corrosion-resistant magnets. In the form of rapidly solidified melt-spun ribbons, FePt-based magnets may exhibit in certain cases a two-phase hard–soft magnetic behaviour. The present paper deals with a microstructural and magnetic study of FePtAgB alloys with increasing Ag content. The aim is to identify and confirm the effect of Ag addition in decreasing the temperature of the FePt disorder–order structural phase transformation. A detailed high-resolution transmission electron microscopy study is employed, and the alternative disposal of hard and soft regions within the two-phase microstructure is observed and interpreted with respect to the X-ray diffraction results. In the as-cast Ag-containing samples, it is shown that there is an optimum of the Ag content for which best magnetic properties are obtained. Ag addition creates a nonlinear behaviour of the coercive field and the ordering parameter, similar to the RKKY interaction-induced interlayer exchange coupling (IEC) observed in magnetic layers separated by non-magnetic spacer layers. Direct formation of the L10 phase from the as-cast state in the FePtAgB alloys is reported with magnetic parameters compatible to other exchange spring permanent nanomagnets. These findings open novel perspectives into utilization of such alloys in applications requiring magnets operating in high-temperature industrial environments. 相似文献
96.
C. Raghu Indranil Rudra Diptiman Sen S. Ramasesha 《Journal of Chemical Sciences》2001,113(5-6):459-486
One of the fascinating fields of study in magnetism in recent years has been the study of quantum phenomena in nanosystems.
While semiconductor structures have provided paradigms of nanosystems from the stand point of electronic phenomena, the synthesis
of high nuclearity transition metal complexes have provided examples of nano magnets. The range and diversity of the properties
exhibited by these systems rivals its electronic counterparts. Qualitative understanding of these phenomena requires only
a knowledge of basic physics, but quantitative study throws up many challenges that are similar to those encountered in the
study of correlated electronic systems. In this article, a brief overview of the current trends in this area are highlighted
and some of the efforts of our group in developing a quantitative understanding of this field are outlined. 相似文献
97.
铜、钛复合添加对结NdFeB磁体显微组织和磁性能的影响 总被引:2,自引:0,他引:2
研究了烧结NdFeB磁体晶间合添加Cu和Ti 对磁体显微组织和磁性能的影响,当钛含量小于1.2%时,Cu和Ti晶间复合添加可大幅度提高烧结NdFeB磁体的矫顽力,磁变化不大,矫顽力的提高归因于Cu和Ti在主相晶粒表面富集,细化晶粒,阻断主相晶粒之间的磁交换作用,阻碍反磁化畴的传播,当钛含量大于1.2%时,矫顽力略有下降,乘磁急剧下降,乘磁下降的原因在于出现了大量的条状纯钛相。与晶间单独合金化相比,晶间复合合金化可更有效改善NdFeB磁体显微组织与性能。 相似文献
98.
Ductile nickel-tungsten (Ni-W) alloys containing about 20–21 at.%W were electroplated onto copper substrates. The development
of the amorphous/nanocrystalline microstructure towards a complete crystallization by isochronal heat treatments in vacuum
was monitored by different methods. For medium annealing temperatures a solid-solution of W in the fcc-Ni lattice was achieved
resulting in an increased hardness. For temperatures of 600 °C and upward recrystallization started and thermodynamically
stable intermetallic compounds like Ni4W and NiW were formed. A third phase, containing more than 80 at.%W was also detected but could not be identified so far.
Only by combination of different methods and especially by use of analytical TEM structural analysis and phase identification
in these amorphous-nanocrystalline Ni-W alloys were successful. 相似文献
99.
Oxide films, 7–10 µm thick, were produced on commercially pure titanium by plasma electrolytic oxidation in a sodium orthophosphate electrolyte using a pulsed unipolar current with frequency (f) and duty cycle (δ) varying within f = 0.1–10 kHz and δ = 0.8–0.2, respectively. The coatings comprised a mixture of an amorphous phase with nanocrystalline anatase and rutile phases, where the relative rutile content range was 17–25 wt%. Incorporation of phosphorus from the electrolyte into the coating in the form of PO2 –, PO3 2– and PO4 3–, as demonstrated by EDX and FT-IR analyses, contributed to the formation of the amorphous phase. Residual stresses associated with the crystalline coating phase constituents were evaluated using the X-ray diffraction sin2 ψ method. It was found that, depending on the treatment parameters, internal direct and shear stresses in anatase ranged from–205 (±17) to–431 (±27) MPa and from–98 (±6) to–145 (±10) MPa, respectively, whereas the rutile structure is comparatively stress-free. 相似文献