Temperature Dependence of Magnetic Compton Profile in DyCo 5
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Temperature Dependence of Magnetic Compton Profile in DyCo5 Hayato Miyagawa, Yasuhiro Watanabe, Akihisa Koizumi1, Nobuhiko Sakai1, Masaichiro Mizumaki2, Yoshiharu Sakurai2, Tetsuya Nakamura3 and Susumu Nanao Institute of Industrial Science, University of Tokyo 7-22-1, Roppongi, Minato-ku, Tokyo 106-8558, Japan 1 Faculty of Science, Himeji Institute of Technology, 3-2-1, Kouto, Kamigori, Ako-gun, Hyogo 678-1297, Japan 2 Japan Synchrotron Radiation Research Institute (JASRI), 1-1-1, Kouto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198, Japan 3 RIKEN (The Institute of Physical and Chemical Research), 2-1, Hirosawa, Wako, Saitama 351-0198, Japan ABSTRACT Magnetic Compton profiles (MCPs) of a DyCo5.4 single crystal were measured at 10 K, 200 K and 300 K. The temperature dependence of the spin moment, which is deduced from the areas under the normalized MCPs, is significantly different from that of the total magnetization measured by a superconducting quantum interference device (SQUID). This difference is due to the presence of a substantial amount of the orbital moment on a Dy site that does not contribute to the magnetic Compton scattering cross section. The analysis of the MCPs reveals that the absolute value of the spin moment increases with increasing temperature and that the spin magnetic moment of the conduction electrons has an opposite sign to the total spin magnetization in the covered range of temperature.
INTRODUCTION Magnetic Compton Scattering (MCS) is a very powerful tool for the study of various magnetic materials[1]. This technique has been demonstrated by Sakai et al. using a γ-ray source [2] for the first time, and then has been developed further since circularly polarized intense x-rays from synchrotron radiation sources have become available. Within the impulse approximation [3], the Compton scattering cross section is proportional to the normal Compton profile (NCP), J(pz), which is defined as the one-dimensional projection of the electron momentum density, n(p), onto the scattering vector taken along the z-axis, J ( p z ) = ∫ ∫ n (p ) dp x dp y = ∫ ∫ [ n↑ (p ) + n↓ (p ) ] dp x dp y ,
(1)
where n (p) and n (p) depending on the momentum are the majority and minority spin densities, respectively. If the incident x-rays are circularly polarized, a small spin-dependence arises in the scattering cross section. Reversing the magnetization of a sample changes the sign of the spin-dependent contribution, which enables us to separate the spin part of the cross section. The resultant profile, known as the magnetic Compton profile (MCP), is a projection of the momentum density of electrons with unpaired spins (Eq. 2). J mag ( p z ) = ∫ ∫ [ n↑ (p ) − n↓ (p) ] dp x dp y
(2)
J(pz) and Jmag(pz) are normalized by the following conditions, GG5.10.1
+∞
∫ J ( p ) dp z
z
=N
(3)
−∞ +∞
∫J
mag
( p z ) dp z = Fs
(4)
−∞
where N and Fs are the number of total electrons and the total spin moment per formula unit, respectively. Therefore, the area of the normalized MCP is proportional to the spin moment. The MCS is
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