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DESCRIPTION:Kazumasa Horigane \, Tohoku University \n\nLayered cobalt oxide
s have attracted much attention due to their wide variety of magnetic\, el
ectrical and structural properties. The parent confound La 2
CoO 4 is an antiferromagnetic insulator with quite high T N =275K. Upon Sr or Ca doping\, a checkerboard Co 2+ -Co 3+ charge order is realized in La 1.5 Ca <
sub> 0.5 CoO 4 and Sr 2 CoO 4 shows a ferromagnetic metal with T c =250K. The background
of these various magnetic states is proposed the relationship of spin stat
e transition from high spin state of Co 3+ (S=3/2) to interme
diate spin state (S=1) [1]. However\, the spin state of Co 3+
is now controversial because there is no direct evidence to observe the m
agnetic scatterings of Co 3+ by using neutron experiment. One
of the big problems in this system is searching for magnetic scattering i
n an elastic condition. In this study\, we measured global spin dynamics (
inelastic condition) in La 1.5 Ca 0.5 CoO
4 using the Fermi chopper spectrometer 4SEASONS in J-PARC [2]. \nFi
gure 1 shows the magnetic excitation of La 1.5 Ca 0.5 <
/sub> CoO 4 below and above T N (=50K). Spin-wave
due to Co 2+ spins is seen up to 16meV below T N
. Another feature of the excitation spectrum is flat mode around 27meV. On
the other hand\, two magnetic modes seem to be merged into single mode ab
ove T N . These results can not be explained by simple spin wav
e theory\, therefore we need to consider another parameters such as Co 3+ spin or angular moment L. In this presentation\, I will discu
ss the origin of this novel magnetic behavior based on the Co 3+ spins and orbital angular moment L. In order to discuss whether there
is a significant orbital angular moment or not in this system\, I will sho
w you the recent research of soft x-ray scattering experiment.\n\n\n[1] Y.
Moritomo\, K. Migashi\, K. Matsuda and A. Nakamura\, Phys. Rev. B 55\, 14
725 (1997)\n[2] M. Nakamura\, R. Kajimoto\, Y. Inamura\, F. Mizuno\, M. Fu
jita\, T. Yokoo and M. Arai\, JPSJ 78\, 093002 (2009)\n
DTSTART:20110127T203000Z
LOCATION:Physics Building\, Room 204
SUMMARY:Study of spin state transition in La 2-x Ca x CoO 4 by using neutron and soft x-ray scattering
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