Y. Hashimoto

Photoinduced precession of magnetization in ferromagnetic (Ga,Mn)As.

Precession of magnetization induced by pulsed optical excitation is observed in a ferromagnetic semiconductor (Ga,Mn)As by time-resolved magneto-optical measurements. It appears as complicated oscillations of a polarization plane of linearly polarized probe pulses, but is reproduced by gyromagnetic theory incorporating an impulsive change in an effective magnetic field due to a change in the magnetic anisotropy. The shape of the impulse suggests a significant nonthermal contribution of photogenerated carriers to the change in anisotropy through spin-orbit interaction.

Analyzing power for proton elastic scattering from the neutron-rich He6 nucleus

Vector analyzing power for the proton-{sup 6}He elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target, which works at a low magnetic field of 0.09 T. The results are found to be incompatible with a t-matrix folding model prediction. Comparisons of the data with g-matrix folding analyses clearly show that the vector analyzing power is sensitive to the nuclear structure model used in the reaction analysis. The {alpha}-core distribution in {sup 6}He is suggested to be a possible key for understanding the nuclear structure sensitivity.

Mapping a magnetization switching field in Ga0.98Mn0.02As microbars with a scanning laser magneto-optical microscope

Local information on 90° magnetization switching in ferromagnetic Ga0.98Mn0.02As microbars with in-plane magnetization was obtained successfully by a homemade scanning laser magneto-optical microscopy. The switching occurs from the edge regions that include edges whose directions are perpendicular to the initial magnetization direction. The local switching field depends strongly on the direction of initial magnetization. The observed results suggest that demagnetization is one of the important factors for magnetization switching in micron-scale (Ga,Mn)As structures.

Investigation of an effective anisotropy field involved in photoinduced precession of magnetization in (Ga,Mn)As

Photoinduced precession of magnetization in (Ga,Mn)As was studied for a wide range of Mn contents (0.01≤x≤0.11) by time-resolved magneto-optical measurements. It was found that an effective anisotropy field decreases with increasing Mn contents. Anisotropy fields were also extracted from photoinduced precession measured at different temperatures and compared with magnetization. Significant enhancement in the amplitude of oscillation in magneto-optical signals occurred with increasing pump power. The mechanism of a change in the anisotropy field with the pump power was discussed.

Elastic Scattering of Neutron-Rich Helium Isotopes from Polarized Protons at 71 MeV/A

The vector analyzing power has been measured for the elastic scattering of neutron-rich 6He and 8He from polarized protons at 71 MeV/A making use of a newly constructed solid polarized proton target operated in a low magnetic field of 0.1 T and at a relatively high temperature of 100 K. An optical model analysis revealed that the spin-orbit potentials for 6He and 8He are characterized by shallow and long-ranged shape compared with the global systematics of stable nuclei. Such a characteristics reflect a diffused density distribution of the neutron-rich isotopes.

Development of Large Deformation in {sup 62}Cr

The structure of neutron-rich isotopes 60Cr and 62Cr was studied via proton inelastic scattering in inverse kinematics. The deformation lengths (delta) for 60Cr and 62Cr were extracted as 1.12(16) and 1.36(14) fm, respectively, providing evidence for enhanced collectivity in these nuclei. An excited state at 1180(10) keV in 62Cr was identified for the first time. We adopted 4;{+} as its spin and parity, leading to the rapid increase of the Ex(4;{+})/E_{x}(2;{+}) ratio, which indicates the development of large deformation in 62Cr near N=40. Importance of the admixture of the gd-shell component above N=40 is also discussed by comparing with a modern shell model calculation.

One-neutron removal reactions of {sup 18}C and {sup 19}C on a proton target

We have studied the one-neutron removal reactions of 18 C at 81 MeV/nucleon and 19 C at 68 MeV/nucleon on a liquid hydrogen target. Transverse-momentum distributions of the core fragments 17 C and 18 C, and their partial cross sections, are measured using coincidences with the y rays. These are compared to theoretical calculations based on the continuum-discretized coupled-channels (CDCC) method. We have found that the transverse-momentum distributions of 17 C are well described by the CDCC calculations, and the agreement provides evidence for the spin-parity assignments of J = 1/2 + for the 0.21-MeV state and J = 5/2 + for the 0.33-MeV state in 17 C. The J = (2, 3) + assignment for the 4.0-MeV state in 18 C is obtained for the first time based on the momentum distribution of 18 C. The measured partial cross sections are consistent with the CDCC calculations combined with shell-model spectroscopic factors. The present study demonstrates that the transverse-momentum distribution obtained in a one-neutron removal reaction on a proton target is as useful as the conventional longitudinal-momentum distribution measured with the heavier Be or C targets for determining the orbital angular momentum of a removed neutron.

Analyzing Power Measurement for Elastic Scattering of 6He on Polarized Protons

Vector analyzing power was measured for the proton elastic scattering on 6He at 71 MeV/u. We applied a solid polarized proton target, which was operated in a low magnetic field of 88 mT and at high temperature of 100 K, to a radioactive‐isotope beam experiment. Low energy recoil protons were successfully detected due to the modest operation conditions of the target. Selection of p+6He elastic scattering events was clearly carried out with detected protons. Absolute values of the analyzing power were determined for the first time.

Invariant-mass spectroscopy of the neutron-drip line nucleus 14Be

We performed an experiment of the inelastic scattering of the two neutron halo nucleus 14Be at 68 A MeV on a carbon target. Since 14Be has no bound excited state, 14Be breaks up into 12Be and two neutrons. Using the invariant-mass method, the first excited state of 14Be is clearly observed at Eex = 1.56(13) MeV. A distorted-wave Born approximation analysis is performed and the spin-parity corresponding to the peak is assigned to be Jπ = 2+. Deformation length of 14Be is extracted to be ∂C = 1.53(10) fm. These experimental results are compared with shell-model calculations.

(p, p′) and (p, n) reactions on halo nuclei

We have measured the 1H(19C,18C+n)1H and 1H(14Be,13B+n)n reactions at 70 MeV/nucleon using the invariant mass method in inverse kinematics. A new state was identified at 1.49 MeV in 19C. In the latter (p, n) reaction, a resonance peak corresponding to the 1.28 MeV state in 14B recently reported in a beta-decay study was clearly observed. Forward peaked character in the differential cross section supports the 1+assignment for this state.