Hiroshi Yamauchi

Bio: Hiroshi Yamauchi is an academic researcher from Tohoku University. The author has contributed to research in topics: Magnetization & Magnetic susceptibility. The author has an hindex of 19, co-authored 68 publications receiving 988 citations.

Single crystal measurements of anisotropy constants of R2Fe14B (R=y, Ce, Pr, Nd, Gd, Tb, Dy and Ho)

Abstract: The first order anisotropy constants Ku1 of the recently found tetragonal rare earth-iron borides R2Fe14B (P42/mnm) have been measured for R=Y, Ce, Pr, Nd, Gd, Tb, Dy and Ho in a magnetic field up to 1600 kA/m from 4.2 K to about 600 K on single crystal samples.

Metamagnetic Phase Transitions in FeTiO 3

Abstract: Magnetic susceptibilities and magnetization isotherms have been measured for single crystal FeTiO 3 The susceptibility parallcl to the c -axis has a large and sharp peak at T N =580±03 K, while the perpendicular susceptibility is almost independent of temperature below T N Magnetization isotherm at 42 K with fields applied along the c -axis exhibits a typical metamagnetic transition at H c =803±01 kOe, being the first observation of metamagnetism in 3 d transition metal oxides The transition is of the first order up to about 35 K, above which it is of the second order The experimental data are well reproduced by molecular field calculations with the best fit parameters of the anisotropy field H A =150 kOe, the ferromagnetic intrasublattice exchange interaction of 2 z 1 J 1 =285 K, and the antiferromagnetic intersublattice interaction of 2 z 2 J 2 =-667 K

Magnetization of α-Phase Fe-Mn Alloys

Abstract: Magnetization measurements of α-phase Fe-Mn alloys, in which manganese concentration is extended up to 11 at% by cold-working techniques, have been made from liquid He temperature to room temperature. The magnetic moment decreases linearly with increasing manganese concentration and assuming that the magnetic moment of iron atom is constant at 2.217 µ B , one obtains the magnetic moment of manganese atom to be 0.8 µ B . On the basis of the spin wave theory, the exchange intergral J and the exchange stiffness constant D are estimated from precision measurements of magnetization at low temperatures.

Mechanical Alloying And Milling

Abstract: Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Organic–Inorganic Perovskites: Structural Versatility for Functional Materials Design

Abstract: Although known since the late 19th century, organic–inorganic perovskites have recently received extraordinary research community attention because of their unique physical properties, which make them promising candidates for application in photovoltaic (PV) and related optoelectronic devices. This review will explore beyond the current focus on three-dimensional (3-D) lead(II) halide perovskites, to highlight the great chemical flexibility and outstanding potential of the broader class of 3-D and lower dimensional organic-based perovskite family for electronic, optical, and energy-based applications as well as fundamental research. The concept of a multifunctional organic–inorganic hybrid, in which the organic and inorganic structural components provide intentional, unique, and hopefully synergistic features to the compound, represents an important contemporary target.

Two-Dimensional Hybrid Halide Perovskites: Principles and Promises.

Abstract: Hybrid halide perovskites have become the “next big thing” in emerging semiconductor materials, as the past decade witnessed their successful application in high-performance photovoltaics. This resurgence has encompassed enormous and widespread development of the three-dimensional (3D) perovskites, spearheaded by CH3NH3PbI3. The next generation of halide perovskites, however, is characterized by reduced dimensionality perovskites, emphasizing the two-dimensional (2D) perovskite derivatives which expand the field into a more diverse subgroup of semiconducting hybrids that possesses even higher tunability and excellent photophysical properties. In this Perspective, we begin with a historical flashback to early reports before the “perovskite fever”, and we follow this original work to its fruition in the present day, where 2D halide perovskites are in the spotlight of current research, offering characteristics desirable in high-performance optoelectronics. We approach the evolution of 2D halide perovskites f...

Magnetization and magnetic anisotropy of R2Fe14B measured on single crystals

Abstract: The temperature dependence of the saturation magnetization and the magnetocrystalline anisotropy field have been measured on single‐crystal samples of the R2Fe14B compounds for R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm from 4.2 K to the magnetic ordering temperatures. A spin reorientation transition of the Nd2Fe14B type has been found in Ho2Fe14B at 57.6 K in zero field. Another type of spin reorientation caused by anisotropy compensation between the Fe and the R sublattices exists in Er2Fe14B and Tm2Fe14B. The temperature dependence of the angle of the easy direction of magnetization from the c axis has been measured for R=Nd, Ho, Er, and Tm. The relation between the magnetocrystalline anisotropy and the sublattice magnetization is investigated by employing a simplified two‐sublattice molecular field model.