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We report on the magnetic, magnetotransport and structural characterization of (Ca1?yNdy)2Fe1+xMo1?xO6 (x 0) of Fe ions in the metallic sublattice produces a remarkable increase, by more than 90?K, of the Curie temperature. M?ssbauer spectroscopy data indicate a reinforcement of the magnetic interactions. We argue that this dramatic enhancement of the ferromagnetic order is due to the strong antiferromagnetic superexchange coupling between near-neighbour Fe?Fe occupying regular and antisite positions in the structure. Moreover, the results indicate that the excess of magnetic ions (Fe) is essential to overcome the dilution effects caused by antisite defects.

Nanostructures have interesting properties due to the confinement of electrons in small structures. In addition, since an appreciable fraction of the electronic wave-function resides outside the physical extension of the nanostructure, proximity effects become more important with decreasing size. Moreover, in magnetic nanostructures the magnetic fields also extend a considerable distance outside the physical extent of the nanostructure. Thus, the interplay between size confinement and proximity effects become particularly interesting in magnetic nanostructures. We give two interesting experimental examples of proximity effects with magnetic nanostructures. In one, small magnetic dots radically modify the magnetotransport properties of superconducting films. In the other, the properties of a ferromagnet with nanoscopic antidots are considerably changed because of proximity with an antiferromagnet.

The magnetic transitions in a thulium single crystal have been investigated with magnetization, AC susceptibility and high-resolution calorimetric measurements. The results give clear evidence of the antiferromagnetic transition at 58 K, the squaring up of the magnetic moments between 42 and 35 K, and the ferrimagnetic transition at 33 K. The transition at 33 K is of first order with a latent heat of 0.8+or-0.2 J mol-1. The magnetic moment in the ferrimagnetic state measured with a SQUID magnetometer is (1.025+or-0.001) consistent with the expected 7.0 mu B per atom and a 3, -4 antiphase domain structure. At 30 kOe afield-induced transition to ferromagnetic order takes place. In this state the moment is found to be (7.060+or-0.001) mu B. The excess moment of 6*10-2 mu B for the ferromagnetic saturation magnetization in thulium is tentatively attributed to polarization of the conduction electrons.

The coupling between hard FePt/CoFe and soft CoFe/NiFe layers through a Cu spacer has been studied in L1(0) (111) FePt(20)/CoFe(1.5)/Cu(3.5or4.5)/CoFe(2)/NiFe(3) (in nm) pseudo spin valves. The sof ...

The microstructural evolution during solid-state sintering of nanocrystalline WC–10 mass% Co powders, prepared by different ball-milling processes to give rise to diverse mechanical activation states, is investigated. During sintering, two ternary carbides, Co6W6C and Co3W3C, form at the binder phase which surrounds WC particle aggregates. The overall microstructure of the sintered material (including the formation of these carbides) is found to be very sensitive to the initial state of the powders, even more than to the sintering temperature and/or sintering time. In addition, the nanocrystalline nature of the composites is preserved during the solid-state sintering, in part assisted by the formation of these complex carbides and decarburization. This nanostructure yields moderate microhardness and fracture toughness values, in spite of the remaining levels of porosity.