Recently, current induced effective magnetic fields in ferromagnetic multilayers have attracted great attention. The effective fields are expected as the way of manipulating magnetic moments in logic and memory devices. However, the origin of these fields has yet to be clearly identified. In order to understand the origin, more experimental investigations on these effective fields are required. In this work, we investigated the effective fields in Fe ferromagnetic multilayers by DC Hall measurements. We show that the method can provide a simple way of measuring the effective fields.
A 1 nm sized CdSe nanoparticle showing a sharp photoabsorption peak at 350 nm has been synthesized in a solution by adding octylamine into a (CdSe)34 solution at low temperature. Solid-state NMR spectra of 113Cd and 77Se show a single narrow peak with large chemical shift anisotropy relating to low symmetry compared with that of bulk CdSe. These results indicate that the constituent atoms of the 1 nm CdSe nanoparticle locate on the surface, and the atomic arrangement deforms from the bulk CdSe structure into an assembly consisting almost entirely of equivalent vertexes.
Exchange-coupled nanocomposite magnets (NCMs) consisting of hard and soft magnetic phases have attracted much attention as novel permanent magnets. We have successfully fabricated the L10-FePd/α-Fe NCMs by the reductive annealing of Pd/γ-Fe2O3 heterostructured nanoparticles. The present study demonstrates the structural optimization of L10-FePd/α-Fe NCMs by adjusting the volume fraction of hard/soft phases and the temperature of reductive annealing to obtain large maximum energy products ((BH)max). The sample with a hard/soft volume ratio of 82/18 formed by annealing at 773 K had the largest (BH)max = 10.3 MGOe. In these L10-FePd/α-Fe NCMs with the large (BH)max, the interface between the hard and soft phases was coherent and the phase sizes were optimized, both of which effectively induced exchange coupling. This exchange coupling was directly observed by visualizing the magnetic interaction between the hard and soft phases using a first-order reversal curve (FORC) diagram.
Ligand-protected gold clusters of around ten metal atoms are expected to exhibit unique properties that depend more or less on the numbers of core atoms and geometric structures. Herein, we show examples of non-spherical gold clusters that exhibit unique optical properties.
Thiolate-protected metal clusters have attracted attention as building blocks for nanostructured materials and devices. Precisely regulating the chemical composition of the surrounding ligands of those clusters is an extremely effective means for their functionalization. However, such a methodology has not been established. We have recently succeeded in precisely and systematically separating metal clusters with two types of thiolate ligands for the first time. The high-resolution separation was achieved by high-performance liquid chromatography (HPLC) combining reverse-phase columns and a mobile phase gradient. The method used to separate individual species showed broad applicability. This study demonstrated the possibility for precise control of the chemical composition of two types of ligands. Given this, we speculate that the control of physical/chemical properties and the sequencing/arrangement of thiolate-protected metal clusters can be achieved at a higher level of precision than what was achievable previously.
Metal α-Fe nanoparticles have long been of technological interest especially in the medical field because of its large magnetization value (218 emu/g). However, it is difficult to keep the metallic state of α-Fe nanoparticles because α-Fe nanoparticles are easily oxidized at the moment of exposure to the atmosphere, and form various iron oxides. In order to make highly stable metallic α-Fe nanoparticles for various applications such as biomedical imaging, sensing or soft phase of the nanocomposite magnet with high-density magnetic energy, the prevention of oxidation is indispensable. In this study, α-Fe nanoparticles with oxide shell were prepared by reduction of SiO2 coated Fe3O4 nanoparticles and partial oxidation of their surfaces. In the case of the α-Fe nanoparticles without surface oxidization, Ms was significantly reduced in one day after treatment. On the other hand, in the case of the partially oxidized α-Fe nanoparticles, decrement of Ms was not observed even after 80 days. From these results, partial oxidation treatment can affect to protect α-Fe phase from oxidization in the air for long time.
Localized surface plasmon resonance (LSPR) of metal nanoparticles has been extensively demonstrated to exhibit large electromagnetic field enhancement localized near the surface of the nanoparticles, especially on the corners and edges, which can be used in applications, such as surface-enhanced Raman scattering (SERS) and fluorescence studies with single molecule sensitivity. In this study, we investigated the synthesis and plasmonic properties of highly monodisperse cubic, rhombic dodecahedral, and octahedral gold nanoparticles. The finitedifference time-domain (FDTD) method was adopted for a comparative study of the electric near-field simulations on the corners and edges of three kinds of nanoparticles to support their SERS activities.
In this review article, we introduce our fluorescent nanothermometers for the accurate measurement of local temperature inside living cells. The first version monitors local temperature changes independent of other environmental parameters such as pH and ionic strength. The second version is able to measure the absolute temperature and to correct the changes in focus by ratiometric measurements. These cationic nanothermometers enter the living cells spontaneously. They revealed thermosensitivity of organelle active transport and inhomogeneous local heat production correlating to Ca2+ changes in single HeLa cells.