Masataka Yamamoto

Synthesis and characterization of novel macrocyclic antimony car☐ylates containing disulfide bonds

Abstract Novel 18- and 22-membered ring cyclic antimony car☐ylates which contained two S S bonds were synthesized in the one-pot oxidative-coupling/condensation reaction of triphenylstibine oxide with thioglycolic or β-thiopropionic acids, respectively.

Rearrangement of crystallographic domains driven by magnetic field in antiferromagnetic CoO

The rearrangement was investigated of crystallographic domains in the antiferromagnetic pseudo-tetragonal phase in CoO (Néel temperature: 293 K) when the domains were driven by a magnetic field. A rearrangement is generally observed in ferromagnetic shape-memory alloys. The rearrangement was found to occur at temperatures between 170 K and 293 K, but not at temperatures below 170 K. In order to determine the reason for such a difference, the shear stress driven by a magnetic field, τ mag, was calculated and compared with the shear stress required for twinning plane movement, τ req. It was found that τ mag is equal to or larger than τ req whenever the rearrangement of crystallographic domains occurs due to the application of a magnetic field, and vice versa. This observation is similar to past observations in the case of many ferromagnetic shape-memory alloys.

Instability of the Parent Phase in Nearly Ordered Fe3Pt Invar Alloys

The martensitic transformation in a nearly ordered Fe3Pt is weak first order, and the martensite phase shows a large magnetic field-induced strain of several percent. We have investigated the origin of this transformation from its electronic structure. A characteristic feature in the electronic structure is the existence of a relatively high peak in the density of states of the minority spin band just below the Fermi energy. This peak splits into two peaks by tetragonal distortion, and one of them shifts to lower energy by the distortion, suggesting that the band Jahn-Teller effect is the main cause for the transformation.

Rearrangement of crystallographic domains driven by magnetic field in ferromagnetic Ni2MnGa and antiferromagnetic CoO

We have investigated the rearrangement of crystallographic domains (martensite variants) in Ni2MnGa ferromagnetic shape memory alloy and CoO antiferromagnetic oxide by applying magnetic field up to 8.0 MA/m. From the result of optical microscope observation of Ni2MnGa single crystal, when a magnetic field is applied along [001]p (p represents a parent phase), the rearrangement of crystallographic domains occurs and the single domain state is obtained below TMs = 202 K. The same rearrangement occurs but partially when a magnetic field is applied along [110]p. On the other hand, when a magnetic field is applied along [111]p, the rearrangement does not occur. In case of the CoO single crystal, when a magnetic field is applied along [001]p below TMs = 293 K, the rearrangement occurs at 170 K ≤ T ≤ 293 K, but does not occur at T < 170 K. When a magnetic field is applied along [110]p and [111]p, the rearrangement does not occur below TMs. In order to explain the rearrangement in the alloy and the oxide, we have evaluated the magnetic shear stress, τmag, which is derived from the difference in magnetic energy among crystallographic domains and have compared it with the shear stress required for the twinning plane movement, τreq. As a result, we have found that the rearrangement occurs when the value of τmag is larger than or equal to the value of τreq for the present alloy and oxide.