We studied three distorted perovskite manganites, ${\mathrm{Pr}}_{1/2}{\mathrm{Sr}}_{1/2}{\mathrm{MnO}}_3$ and ${\mathrm{Nd}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ with $x=1\mathrm{}/2$ and 0.55 by the neutron diffraction technique. Two samples with $x=1\mathrm{}/2$ exhibit a transition from a ferromagnetic (FM) metal to an antiferromagnetic (AFM) nonmetal. We demonstrate that, in the low temperature phase, ${\mathrm{Nd}}_{1/2}{\mathrm{Sr}}_{1/2}{\mathrm{MnO}}_3$ has a CE-type AFM structure with charge ordering, while ${\mathrm{Pr}}_{1/2}{\mathrm{Sr}}_{1/2}{\mathrm{MnO}}_3$ and ${\mathrm{Nd}}_{0.45}{\mathrm{Sr}}_{0.55}{\mathrm{MnO}}_3$ exhibit an $A$-type layered AFM structure, but show no clear sign of charge ordering. From the present results, we suggest a possible anisotropy of transport as well as magnetic properties in the $A$-type AFM structure near $x\sim 1/2$.

We have peformed neutron diffraction measurements on melt-grown polycrystalline samples of ${\mathrm{Nd}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ $(0.49\mathrm{}<~x<~0.75).$ A systematic transformation of the crystalline and magnetic structures of this system was observed. This can be consistently explained by the change of the character of the Mn $e_g$ orbitals. When increasing X, the ${\mathrm{Nd}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ system exhibits an evolution from a metallic ferromagnetic state, to a metallic A-type antiferromagnetic (AFM), and then to an insulating C-type AFM state. The CE-type charge-ordered AFM state was observed only in the vicinity of $x=1/2\mathrm{}$ and it coexists with the A-type AFM state for $x\gtrsim 1/2,$ indicating that the energy difference between these two states is very small. We also found that the ${\mathrm{MnO}}_6$ octahedra are apically compressed in the CE-type and A-type AFM states due to the ${d(3x}^2-r^2{)/d(3y}^2-r^2)$ or ${d(x}^2-y^2)$ orbital ordering, whereas they are apically elongated by the rod-type ${d(3z}^2-r^2)$ orbital ordering in the C-type AFM state. Finally, a selective broadening of Bragg peaks was observed in the C-type AFM phase and its x dependence strongly suggests the onset of charge ordering for either $x=4/5\mathrm{}$ or $x=3/4.\mathrm{}$

AMATERAS is a new disk-chopper-type spectrometer installed at Materials and Life Science Experimental Facility (MLF) of J-PARC. AMATERAS is equipped with an extra chopper for pulse shaping at the upstream position, in addition to a monochromating chopper, which conventional chopper spectrometers at pulsed source have. Owing to the use of these choppers and the high peak intensity from a coupled moderator source at MLF, the AMATERAS design realizes high-intensity and high-energy-resolution measurements in quasielastic and inelastic neutron scattering experiments. The spectrometer had the first neutron beam in May 2009. During the course of commissioning, the performance of the spectrometer was confirmed by conducting test experiments. AMATERAS is now open to users and is producing scientific outputs.

4SEASONS is a Fermi chopper spectrometer in operation at the Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC). 4SEASONS is expected to facilitate high-efficiency measurements of weak inelastic signals on novel spin and lattice dynamics using thermal neutrons. The spectrometer is equipped with a coupled moderator and sophisticated components such as an elliptical converging neutron guide with high-critical-angle supermirrors, long (2.5 m) position-sensitive detectors, and a Fermi chopper appropriate for multiple-incident-energy (multi- E i ) measurements by the repetition-rate multiplication technique. Herein, we discuss in detail the design and performance of the spectrometer, and present some examples of the measurements obtained using this spectrometer.

We have investigated the magnetic structure of an insulating lightly doped ${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{MnO}}_3$ with x=0.04,0.125, and 0.17 with neutron scattering technique and bulk magnetization measurements. The magnetic structure of the x=0.04 sample at 5 K is a commensurate layer-type (A-type) antiferromagnetism with the propagation vector [010] and the moment of 3.7±0.2${\mathrm{\mu }}_{\mathit{B}}$/Mn, being parallel to the [100] axis in the orthorhombic Pnma symmetry. In addition, a spontaneous magnetization of 0.28±0.02${\mathrm{\mu }}_{\mathit{B}}$/Mn is observed at 8 K by magnetization measurement. By contrast, the x=0.125 sample exhibits a large ferromagnetic moment of 3.7±0.2${\mathrm{\mu }}_{\mathit{B}}$/Mn and a small A-type antiferromagnetic component of 0.23±0.1${\mathrm{\mu }}_{\mathit{B}}$/Mn, while the x=0.17 sample exhibits only a ferromagnetic component of 3.6±0.2${\mathrm{\mu }}_{\mathit{B}}$/Mn. These results are consistent with a spin structure derived from the conventional double exchange mechanism, but rule out the possibility of a recently suggested spiral spin structure for the insulating ${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{MnO}}_3$ system. © 1996 The American Physical Society.