Comparison of Magnetic and Electrical Properties in Amorphous, Quasicrystalline and Crystalline States of Al-Mn Alloys

The magnetic and electrical properties in the amorphous, quasicrystalline and crystalline states of Al-Mn and Al-Mn-Si alloys have been investigated and compared because the amorphous structure is often correlated with the icosahedral structure, and the structures of some crystalline compounds are resemble to that of the quasicrystalline alloys. The magnetizations measured up to 300 kOe for the amorphous alloys are slightly larger than those of the quasicrystalline alloys, and the paramagnetic Curie temperature of the former alloys is larger than that of the latter alloys. The magnitude of effective magnetic moment P_ determined from the Curie-Weiss law for crystalline alloys is qualitatively explained in terms of the Pauling valence. The value of P_ of the quasicrystalline alloys is almost the same as that of the amorphous ones and about two times that of the crystalline alloys at the same composition. From the magnetic measurements it becomes clear that Mn sites are partly magnetic, and the magnetic properties are drastically modified by substituting some fraction of Mn for other transition metals such as Cr. The spin-glass behavior is observed and the spin freezing temperature lies on the same line as a function of Mn content for both the amorphous and quasicrystalline alloys. The electrical resistivity of the quasicrystalline alloys with a relatively high Mn content is extremely large accompanying a negative temperature coefficient as that of the amorphous alloys. After crystallization, its magnitude is reduced drastically and the temperature dependence curves of the alloys with high concentrations show a positive curvature in the wide temperature range. Therefore, the magnitude and the temperature dependence of electrical resistivity of the quasicrystalline alloys are very different from those of the crystalline alloys. From these results, it is concluded that the magnetic and electrical properties of Al-Mn quasicrystalline alloys are very similar to those of amorphous ones and distinctly different from those of the crystalline alloys

Optical Measurement Techniques under Shock Compression using Rotating Mirror Type Streak Camera

An optical measuring system by means of streak photography has been developed to obtain precise Hugoniot equation of state and optical absorption spectra of solids under shock compression using the two-stage light gus gun described in the preceding paper. The system utilizes light from a 1 kJ high intensity xenon flash lamp with about 10 torr Xe filling pressure. A continuous writing streak camera of rotating mirror type with a maximum writing rate of 13.5 mm/μs has been constructed to observe nonsynchronizable shock phenomena produced with the gun. The streak camera with a slit 23 μm in width (which corresponds to the slit image 92 μm in width on the film) is currently operated at the writing rate 10 mm/μs. Hugoniot equation of state is determined with an accuracy ±1% using the inclined mirror technique. The release adiabat (i.e. adiabatic release path) from the shock compressed state is measured with the buffer technique. An optical absorption spectrographic system has a spectral response of 300-700 nm and wavelength dispersion of 8.3 nm/mm on the film

Production of Ultrahigh Magnetic Fields by Explosive-Driven Flux Compression

Magnetic fields exceeding 1 MOe are reproducibly generated by a flux compression method using a cylindrical metal liner and high explosives. Some new devices are employed for simultaneous initiation of the cylindrical explosive on its outer surface. Detailed measurements are made on the dependence of the liner velocity on the mass ratio of liner and explosive. The results are consistent with an analysis based on the theory of detonation

Shock Compression Experiments in Solids using High Explosives

Small-scale explosive plane wave generators, 40-78 mm in diameter, are developed to perform solid state experiments at shock pressures up to 1 Mbar. Techniques for determining the shock compression curve are described in detail, especially in the case where a phase transformation occurs at a high pressure

Magnetic Moment and Spin Glass Behavior of AlCuMn and AlPdMn Quasicrystalline and Amorphous Alloys((B)Quasicrystals)

In the present review, the effective magnetic moment, the magnetic Mn atom ratio, partial substitution of TM and the spin glass behavior of AlCuMn, AlPdMn and AlMn quasicrystalline and amorphous alloys are discussed. Distinct differences in the magnetic properties between quasicrystalline and amorphous states have been confirmed in AlCuMn and AlPdMn alloy systems in contrast with those in AlMn alloys. The effective magnetic moments of AlCuMn and AlPdMn quasicrystalline alloys are smaller than those of amorphous counterparts, but much larger than those of AlMn alloys in the same concentration range. The ratios of magnetic Mn atoms in AlCuMn and AlPdMn quasicrystalline alloys are about one half that of the amorphous counterparts, although there is no essential distinction in AlMn alloy systems. The spin glass behavior has been confirmed in AlCuMn amorphous alloys and AlPdMn quasicrystalline and amorphous alloys even below 15 %Mn, although AlMn alloys exhibit the spin glass behavior above 20 %Mn. These differences mentioned above can be explained by considering the difference in the forming ability of the localized magnetic moment among three alloy systems and in the local structure between the quasicrystalline and amorphous states. It should be noted that Al_Pd_Mn_ quasicrystalline alloy has a giant magnetic moment in analogy with PdMn crystalline dilute alloys

High-Sensitivity Streak Camera Applicable to Time-Resolved Spectroscopy

A high-sensitivity streak camera has been designed and manufactured using a photoelectric tube with deflecting plates and a microchannel plate which serves as both a streak device and an image intensifier. Characteristics of the complete equipments are as follows : (1) an image on the film is 10.2 times as large as an image on the photoelectric surface, (2) effective area of the film is 45 mm in diameter, (3) resolution on the film is 2.5 lp/mm (4) writing speed on the film is 0.2～20 mm/μs, 5-stage variable, (5) sensitivity is controlled by the microchannel plate voltage, and (6) a spectroscope is combined to take time-resolved spectrographs, 1 mm on the film corresponding to 0.9 nm of the wavelength

A Two-Stage Light Gas Gun for Shock Wave Research

A two-stage light gas gun of 9 m length is constructed for shock wave research. The apparatus consisted of a 60 mm inner-diameter and 3.6 m long pump stage and a 20 mm inner-diameter and 3.4 m long launch stage. A flyer plate bearing 10 g projectile is accelerated to 4.1 km/s using 120 g propellant charge. Using tungsten flyer plate, shock pressure of 2.5 Mbar is generated. For the velocity range between 2 to 4 km/s, the reproducibility of the muzzle velocity is proved to be within 3%. Details of the projectile and piston design, target alignment procedure and projectile velocity measuring system are described

Magnetic Phase Transition and Magnetization Plateau in Cs2_2CuBr4_4

The crystal structure of Cs$_2$CuBr$_4$ is the same as that of Cs$_2$CuCl$_4$, which has been characterized as a spin-1/2 quasi-two-dimensional frustrated system. The magnetic properties of Cs$_2$CuBr$_4$ were investigated by magnetization and specific heat measurements. The phase transition at zero magnetic field was detected at $T_{\rm N}=1.4$ K. It was observed that the magnetization curve has a plateau at about one-third of the saturation magnetization for magnetic field $H$ parallel to the $b$- and $c$-axes, while no plateau was observed for $H\parallel a$. The field-induced phase transition to the plateau state appears to be of the first order. The mechanism leading to the magnetization plateau is discussed.Comment: 6 pages, 4 figures, 4 eps files, ptptex, will appear in Supplement of Progress in Theoretical Physic

Shock Compression of Titanium Monoxide up to 600 kbar(Physics)

Hugoniot data were obtained for titanium monoxide TiO_x (x=0.84, 1.06, and 1.28), up to about 600 kbar by shock wave compression. A small explosive lens system was used for the purpose of generating plane shock waves. Shock velocities and free surface velocities were measured by means of an electric pin-contactor method ; the shock state was computed on the basis of free surface approximation. Regardless of the values of x, the compounds TiO_x were shown to be extremely incompressible even in this ultrahigh pressure region ; no evidence was found for significant filling of vacancies

Magnetic Field Effects on the Electrochemical Potential(Research in High Magnetic Fields)

A novel magnetic field effect on chemical systems has been studied : The equilibrium potential was influenced by magnetic fields for the electrochemical systems including ferromagnetic hydrides such as LaCo_5H_x and Y_2Co_7H_x. The change in the electrode potential ΔE for ferromagnetic hydrides was proportional to magnetic fields and ΔE was independent of the direction of the magnetic field. A 1.7mV decrease in the potential was observed for the LaCo_5H_x electrode at 15T at 293.2K. The results agree well with the thermodynamic theory where the free energy of the system includes the magnetostatic energy