S. Chikazumi

ELECTRON MICROSCOPY OF ORTHORHOMBIC PHASE IN MAGNETITE

An electron microscopic observation on a synthetic single crystal of magnetite has been carried out at a temperature range between 77°K and room temperature. It was observed that the ordered phases below the low‐temperature transition appear as finely divided stripes. The diffraction patterns in one of the stripes show the extra spots such as (00½), (100), (010), or (11½) in cubic indices. This indicates that the unit cell of the low‐temperature phase should be twice as large as that proposed by Verwey. The ordering scheme proposed should be more complicated than the Verwey order.

The Invar Problem

Anomalous thermal expansion and its relation to magnetic properties are surveyed for various Invar alloys. Saturation magnetization was measured for alloy systems (FexNi1−x)92M8, where M=Cu, Co, Mn, Cr, and V, and also for Fe70(RexPt1−x)30 at 4.2°K. Sharp drop of the saturation moment occurs at the average electron concentration, N=8.13 to 8.52, for all the Invar alloys including the above‐mentioned alloy systems and N=8.21 to 8.52 for all the Fe–Ni base alloys. When, however, it was plotted against the electron concentration of the matrix surrounding less electropositive impurity atoms such as Mn, Cr, or V, all the alloy systems were found to exhibit a sharp drop of the moment in narrower concentration range of 8.48 to 8.60 for all the Fe–Ni base alloys. Saturation moment and a reversible susceptibility in the saturation range were also measured at room temperature for (110) [001] and (001) [110] rolled single crystals of the composition 29 at.% Ni–Fe. It was found that saturation moment was reduced from...

Neutron Scattering from Low-Temperature Phase of Magnetite

A high resolution neutron scattering study has been carried out on the charge ordering of magnetite below 123 K. Magnetic components were separated out by the application of magnetic field perpendicular to the c -axis which had been aligned by field cooling. Non-zero magnetic scattering was observed at (2, 0, l +1/2) referred to the cubic lattice, but not at (0, 0, 2), in contradiction to the previous report by Hamilton. This magnetic intensity distribution suggests the alternate Fe 2+ and Fe 3+ in the a b plane, in contrast to the Verwey model of the single modulation along the c -axis. Substantial disagreement remains between observed magnetic intensities and simple model calculations and further experiments are suggested to resolve this difficulty.

Technique for measuring infrared cyclotron resonance in ultrahigh magnetic fields

A technique is described for giving accurate measurements of cyclotron resonance and Faraday rotation in very high pulsed magnetic fields up to 130 T (1.3 MG). The megagauss fields were generated by the compression of magnetic flux with electromagnetic force in the theta -pinch configuration (Cnare (1966) effect). A tunable CO2 laser was used for the infrared light source, and fast detection of the light was carried out with a high speed infrared detector. A simple method was developed for determining accurately the relative field sensitivity of pickup probes. Based on the calibration of the absolute field sensitivity of the probes by the Faraday rotation of CdS at 632.8 nm, the accuracy of the field intensity measurements reached +or-3%. The cyclotron resonance for electrons in Ge, GaAs and InSb was measured at room temperature.

Magnetic and thermal anomalies of Invar alloys

The anomalous volume contraction ωa(T) of Fe‐Ni and Fe‐Pt Invar alloys were analyzed in terms of the Gruneisen equation using the experimental data of thermal expansion coefficient. It was found that ωa(T) increases with increasing Fe composition or temperature and remains nonzero even above the Curie point ϑu2009f for both the Invar alloys. The susceptibility of Fe‐Ni alloys and the magnetization of Fe‐Pd alloys were measured. The magnetic anomalies of Invar alloys are summarized. A calculation by molecular field theory in terms of a high and low spin state transition model can well explain the anomalous isothermal magnetization curve and the anomalous volume contraction as well as instability of ferromagnetism, where the center of the low spin state has higher energy than the high spin state at high temperatures and the distribution of low spin state energy and the exchange field of the high spin state were considered. From the x‐ray diffraction experiments at low temperatures, an anomalous random static di...

Infrared cyclotron resonance in InSb, GaAs and Ge in very high magnetic fields

Abstract Infrared cyclotron resonance was observed in n -type InSb, GaAs and Ge in very high magnetic fields up to 1.3 MOe at room temperature using a CO 2 laser. A large shift of the cyclotron mass due to the non-parabolicity of the energy band was found in each material. The band edge masses of electrons at room temperature were evaluated to be m ∗ = 0.0127 m for InSb, m ∗ = 0.065 m for GaAs and m ∗ t = 0.086 m for Ge. The linewidth was measured in GaAs and Ge in the high fields.

Effect of Ti-Impurities on Ferromagnetic Properties of Fe, Co and Ni

Saturation magnetization, Curie temperature, magnetocrystalline anisotropy and magnetostriction were measured for M 1-c Ti c (M=Fe, Co, Ni) systems. The rate of change in saturation magnetic moment dµ/d c at 0 K was found to be -6.2 µ B and -4.3 µ B per atom in Co–Ti and Ni–Ti systems, respectively. For Fe–Ti system the decrease in magnetic moment was non-linear. Curie temperatures of Ni–Ti system decrease monotonically at the rate of -42 K per atomic percent Ti and those of Fe–Ti system increase linearly at the rate of +3.7 K per atomic percent Ti. Magnetostriction and magnetocrystalline anisotropy of Fe–Ti system also increase with increasing Ti concentration.

Production of magnetic fields in megagauss region and related measuring techniques

Using the Cnare effect or the electromagnetic compression of magnetic flux with a metal liner, very high magnetic fields up to 2.8 MG (or 280 T) have been successfully produced in a pulse form with a rise time of several μs. Observation of a motion of the liner and a process of field generation were in good agreement with computer simulation. Measurement of field intensity was performed by integrating a pulse signal induced in a few turn pickup coil and also by observing Faraday rotation for CdS crystal. Direct measurement of magnetization was performed in submegagauss region by integrating a voltage induced in a search coil by means of a cascade integrator, which ensures a high fidelity amplification. In megagauss region, where B gg I , magnetization process was observed by measuring reversible susceptibility by a high-frequency pulse technique. Some magnetooptical observation is also described. Significance of megagauss fields in solid state physics is discussed. A future project aiming the production of 10 MG (or 1000 T) is also discussed.

Evolution of research in magnetism in Japan

After describing historical achievements by J. A. Ewing, K. Honda, S. Kaya and their coworkers, important inventions, research, and improvement of various magnetic materials which have been made in Japan are introduced. Then physical studies of various magnetic phenomena, such as domain observations, atomic order and induced anisotropies, the Invar Problems, the low temperature phase of magnetite, and studies related to other magnetic compounds are described. Finally achievements on magnetic theories mainly by T. Nagamiya and his disciples are briefly introduced.

Roll Magnetic Anisotropy of Iron-Aluminum Crystals

Magnetic anisotropy measurements and domain pattern observations were made on the rolled Fe3Al single crystals. Rolling parallel to [001] on a (110) plane induced a uniaxial anisotropy as large as 7.1×105u2009erg/cc at 12% roll-reduction. The direction of easy magnetization was parallel to the roll direction. Calculations were made on the roll magnetic anisotropy in terms of the “slip-induced directional order model,” under the assumption of (110) (111) slip system. (110) [110], (001) [010], and (001) [110] rollings were also investigated.