Shigenori Numao

Chromium acetylide complex based ferrimagnet and weak ferromagnet.

The crystal structures and magnetic properties of new molecule-based magnets, [CrCyclam(C[triple bond]C-3-thiophene)(2)][Ni(mdt)(2)] (1) and [CrCyclam(C[triple bond]C-Ph)(2)][Ni(mdt)(2)](H(2)O) (2) (Cyclam = 1,4,8,11-tetraazacyclotetradecane, mdt = 1,3-dithiole-4,5-dithiolate), are reported. The crystal structures of both compounds are characterized by ferrimagnetic chains of alternately stacked [CrCyclam(C[triple bond]C-R)](+) cations and [Ni(mdt)(2)](-) anions with intrachain exchange interactions of 2J = -6.1 K in 1 and -5.7 K in 2 (H = -2J Sigma(i) S(i) x S(i+1)). The material 1 exhibits ferrimagnetic transition at 2.3 K owing to weak interchain antiferromagnetic interactions between cations and anions. In the case of 2, cations in adjacent ferrimagnetic chains are bridged by a water molecule, resulting in an interchain antiferromagnetic coupling. Despite a centrosymmetry of a whole crystal of 2, one bridging water molecule occupies only one of the two centrosymmetric sites and breaks a local centrosymmetry between adjacent cations. The interchain antiferromagnetic interaction and Dzyaloshinsky-Moriya interaction originated from the local symmetry breakdown of 2 bring a weak-ferromagnetic transition at 3.7 K with a coercive force of less than 0.8 mT, followed by the second magnetic phase transition at 2.9 K. Below this temperature, the coercive force rapidly increases from 1 to 11.8 mT as the temperature decreases from 2.9 to 1.8 K, while the remanent magnetization monotonically increases from 0.008 mu(B) at 3.6 K to 0.12 mu(B) at 1.8 K.

Increased Electric Conductance through Physisorbed Oxygen on Copper Nanocables Sheathed in Carbon

Adsorption of molecules onto solid surfaces can be classified into physisorption and chemisorption. Physisorbed molecules are so weakly bound to surfaces that adsorption and desorption can proceed reversibly even at room temperature. By contrast, chemisorption is accompanied by chemical bond formation, and higher temperatures are necessary for desorption. Solid gas sensors are normally based on chemisorption for modification of the electronic band conduction. We found that copper nanocables sheathed in carbon can detect physisorbed oxygen at room temperature by just measuring electric resistance. The sensing principle based on hopping conduction is specific to nanomaterials and enables detection of physisorbed oxygen.