Magnetically Superior and Easy to Handle L10-FePt Nanocrystals

We report a successful synthesis of monodisperse L10-FePt nanocrystals which are not only superior in magnetism but also easy to handle through being dispersible in solvents. Thanks to a thick SiO2-coating, the thermal treatment needed to form the L10 structure can be done even at 900 oC without inducing coalescence and coarsening. The protecting shell was thereafter removed in a specific way that enabled us to recover the L10-FePt nanocrystals in a water-dispersion. The SiO2-coated nanocrystals show a high coercivity of 18.5 kOe at room temperature in spite of their core size of only 6.5 nm in diameter, and the hysteresis loop of the water-dispersed nanocrystals, which were frozen under an external field, was almost rectangular indicating that their magnetic and structural orientation could be attained.Comment: 14 pages, 5 figure

Microscopic Characterization of the L10-FePt Nanoparticles Synthesized by the SiO2-Nanoreactor Method

We investigated magnetic properties of the L10-FePt nanoparticles synthesized by the SiO2-nanoreactor method by means of Moessbauer spectroscopy from the microscopic point of view. Almost all of the nanoparticles were revealed to have nearly the same Moessbauer hyperfine parameters as those of the bulk L10-FePt alloy, indicating that they have well-defined L10 structure equivalent to the bulk state in spite of their small size of 6.5 nm.Comment: 13 pages, 4 figure

Formation of random singlets in the nanocrystalline quasi-one-dimensional spin-1/2 antiferromagnet Sr21Bi8Cu2(CO3)2O41

Induced by quenched disorder, random-singlet states occur in a variety of low-dimensional spin-1/2 antiferromagnets, some of them candidates for quantum spin liquids. Here we report measurements of the specific heat, magnetization, and magnetic susceptibility of nanocrystalline Sr21Bi8Cu2(CO3)2O41, a quasi-one-dimensional spin-1/2 antiferromagnet with alternating bonds. The results uncover the predominant presence of random-singlet spin pairs in this material, with a logarithmic probability distribution, P(J), of the renormalized, emergent exchange interaction, J, in zero magnetic field and P(J) proportional to 1/J in magnetic fields. We postulate that these unexpected J dependences, in contrast to the usual P(J) \propto 1/$J^\gamma$ with 0 < $\gamma$ < 1, and possibly also the dichotomy, arise from the finite size of the nanocrystals. Scaling functions for the specific heat and magnetization reproduce our magnetocaloric-effect data, with no adjustable parameters

ソクド チョウリョク ノ ビショウ ヘンカ ケンシュツ ト ソノ オウヨウ

A sinker with a non-stretched fine flexible string fall down with the sinker naturally, and both the speed and tension of its drawing-out string are individually measured. It is thought that a sinker will meet with an obstacle, if both sudden irregularities are observed at the same time upon motion of the string. In this case, a general stepping motor are employed in measurments of the speed and a tork-less special encorder are used in detection of the tension as sensors

ネツ ルミネッセンス 2ジゲン ヨミトリ システム

熱ルミネッセンス[TL]2次元読み取りシステムを開発した。このシステムを使った応用として, 人工のTL-sheet(BaSO_4 : Eu)を用いて高エネルギー宇宙線シャワーの検出を行なった例と, 天然の試料(鍾乳石, 花崗岩)のTL空間分布を測定した例を示す.A spatial distribution read-out system of thermoluminescence [TL] is developed. This system is applied to artificial TL-sheets (BaSO_4 : Eu) for detecting high energy cosmic ray showers and to inhomogeneous materials for measuring natural TL spatial distributions of stalactite and Mannari-granite