N. Kawamoto

Strong magnetocaloric effects in La1−zCez(Fex−yMnySi1−x)13 at low temperatures

The Curie temperature TC of La1−zCez(Fex−yMnySi1−x)13 is decreased by adjusting the composition, and hence the itinerant-electron metamagnetic transition is observed at 5K in La0.75Ce0.25(Fe0.850Mn0.035Si0.110)13 after zero-field cooling. As a result, the La1−zCez(FexMnySi1−x)13 compounds exhibit strong magnetocaloric effects in relatively low magnetic fields in a wide range of temperatures between about 19 and 180K. Consequently, the La1−zCez(Fex−yMnySi1−x)13 compounds are useful for the magnetic refrigerants working at low temperatures.

Local conductivity and electric field analysis of Ag-based conductive adhesive by transmission electron microscopy

The conduction mechanism in Ag-based conductive adhesive, which has attracted the attention of researchers, has been intensively studied by the in situ observations of transmission electron microscopy (TEM) and by using special methods that employ the use of microprobes; Ag-based conductive adhesive is considered as an alternative to Pb-free solders. A current versus voltage (I-V) curve measured by using a microscope exhibited peculiar fluctuations, which implied an irreversible change in the internal structure of a cured adhesive. TEM observations showed a local shape change in Ag agglomerations, such as the formation of small horns, in a sample that was subjected to a large electric current of 1u2002μA. Electron holography data, which revealed the inhomogeneous distribution of equipotential lines in the sample, also implied an essential role of morphological change in the conduction properties of Ag-based conductive adhesive.

Magnetic domains in a metamagnetic La(Fe0.90Si0.10)13 refrigerant

A thermally induced first-order magnetic phase transition in La(Fe0.90Si0.10)13 has been observed in situ by using Lorentz microscopy in the Fresnel mode. On cooling the specimen, the magnetic domains instantly are formed at the Curie temperature TC as in a fashion of the first-order phase transition. The coexistence of the ferromagnetic and paramagnetic phases was observed at TC, and the phase boundary was confirmed to be located at the grain boundaries. In addition, the observed magnetic domain structure is reproduced without any change even after repeating thermal cycles in the vicinity of TC. This fact strongly implies that the phase transition during thermal cycles does not induce lattice defects which cause serious deterioration.

Microstructure and conductivity analysis of silver-based conductive adhesive by TEM with double-probe piezodriving holder

Microstructure of Ag-epoxy conductive adhesive, which is expected as a substitution for Pb-free solder, has been investigated by electron microscopy. The observations have demonstrated the presence of agglomerations of Ag particles, and they are likely to be connected to form huge conduction paths in a solidified state. Moreover, multidisciplinary tests (e.g., simultaneous examination of the microstructure and electric resistivity) on the solidified adhesives were performed inside the transmission electron microscope with the aid of mobile microprobes.