Nanometer-size hard magnetic ferrite exhibiting high optical-transparency and nonlinear optical-magnetoelectric effect

Development of nanometer-sized magnetic particles exhibiting a large coercive field (Hc) is in high demand for densification of magnetic recording. Herein, we report a single-nanosize (i.e., less than ten nanometers across) hard magnetic ferrite. This magnetic ferrite is composed of ε-Fe2O3, with a sufficiently high Hc value for magnetic recording systems and a remarkably high magnetic anisotropy constant of 7.7 × 106 erg cm−3. For example, 8.2-nm nanoparticles have an Hc value of 5.2 kOe at room temperature. A colloidal solution of these nanoparticles possesses a light orange color due to a wide band gap of 2.9 eV (430 nm), indicating a possibility of transparent magnetic pigments. Additionally, we have observed magnetization-induced second harmonic generation (MSHG). The nonlinear optical-magnetoelectric effect of the present polar magnetic nanocrystal was quite strong. These findings have been demonstrated in a simple iron oxide, which is highly significant from the viewpoints of economic cost and mass production.UTokyo Research掲載「世界最小ハードフェライト磁石の開発に成功」 URI: http://www.u-tokyo.ac.jp/ja/utokyo-research/research-news/the-worlds-smallest-hard-ferrite-magnet.htmlUTokyo Research "The world\u27s smallest hard ferrite magnet" URI: http://www.u-tokyo.ac.jp/en/utokyo-research/research-news/the-worlds-smallest-hard-ferrite-magnet.htm

A Novel Technique for Controlling Anisotropic Ion Diffusion : Bulk Single-Crystalline Metallic Silicon Clathrate

Na-free Si clathrates consisting only of Si cages are an allotrope of diamond-structured Si. This material is promising for various device applications, such as next-generation photovoltaics. The probable technique for synthesizing Na-free Si clathrates is to extract Na+ from the Si cages of Na24Si136. Vacuum annealing is presently a well-known conventional and effective approach for extracting Na. However, this study demonstrates that Na+ cannot be extracted from the surface of a single-crystalline type-II metallic Si clathrate (Na24Si136) in areas deeper than 150 mu m. Therefore, a novel method is developed to control anisotropic ion diffusion: this is effective for various compounds with a large difference in the bonding strength between their constituent elements, such as Na24Si136 composed of covalent Si cages and weakly trapped Na+. By skillfully exploiting the difference in the chemical potentials as a driving force, Na+ is homogeneously extracted regardless of the size of the single crystal while maintaining high crystallinity. Additionally, the proposed point defect model is evaluated via density functional theory, and the migration of Na+ between the Si cages is explained. It is expected that the developed experimental and computational techniques would significantly advance material design for synthesizing thermodynamically metastable materials

Robustness of Voltage-induced Magnetocapacitance

One of the most important achievements in the field of spintronics is the development of magnetic tunnel junctions (MTJs). MTJs exhibit a large tunneling magnetoresistance (TMR). However, TMR is strongly dependent on biasing voltage, generally, decreasing with applying bias. The rapid decay of TMR was a major deficiency of MTJs. Here we report a new phenomenon at room temperature, in which the tunneling magnetocapacitance (TMC) increases with biasing voltage in an MTJ system based on Co40Fe40B20/Mgo/Co40Fe40B20 . We have observed a maximum TMC value of 102% under appropriate biasing, which is the largest voltage-induced TMC effect ever reported for MTJs. We have found excellent agreement between theory and experiment for the bipolar biasing regions using Debye-Frohlich model combined with quartic barrier approximation and spin-dependent drift-diffusion model. Based on our calculation, we predict that the voltage-induced TMC ratio could reach 1100% in MTJs with a corresponding TMR value of 604%. Our work has provided a new understanding on the voltage-induced AC spin-dependent transport in MTJs. The results reported here may open a novel pathway for spintronics applications, e.g., non-volatile memories and spin logic circuits

Magnetic lotus root based on a cyanido-bridged Co–W metal assembly

An octacyanidometalate-based nanochannel magnet, Co₇[W­(CN)₈]₄Cl₂·29H₂O, is reported. Single-crystal synchrotron X-ray diffraction measurements reveal that this compound has a three-dimensional cyanido-bridged network based on {Co₅W₄}_n columns situated along the <i>c</i>-axis. The channels resemble a lotus root and have a remarkably large diameter of 1.4 nm, which corresponds to a 44% vacancy. Although the channel size is very large, the compound exhibits ferromagnetic ordering with a Curie temperature of 29 K and coercive field of 5500 Oe. Such a ferromagnetic lotus root can adsorb large molecules and may realize host–guest chemistry in ferromagnets

Pancreaticoduodenectomy for an Ampullary Region Carcinoma Occurred in Annular Pancreas Coexistent with Replaced Common Hepatic Artery

Introduction. Annular pancreas is a rare congenital abnormality characterized by a ring of pancreatic tissue surrounding the descending portion of the duodenum. Annular pancreas coexisting with replaced common hepatic artery which is also a rare anatomical variation has not been reported previously. Case Presentation. A 53-year-old man visited our hospital complaining of epigastric pain. Based on radiological examinations, he was diagnosed as having pancreatitis, annular pancreas, and hepatomesenteric trunk. One month later, obstructive jaundice developed. Endoscopic examination revealed ampullary region carcinoma. We performed pancreaticoduodenectomy using the “artery-first” approach. Discussion. Both annular pancreas and common hepatic artery anomaly are rare. High-quality preoperative imaging and awareness of such rare conditions are necessary for operative safety. Although the embryological relationship between these anomalies is uncertain, the present case may suggest some relevance between the two. Conclusion. The “artery-first” approach may be a useful method for pancreaticoduodenectomy in patients who have an anatomical abnormality