大型放射光施設 SPring-8

問い合わせ番号

INS-0000000299

  Magnetic circular dichroism (MCD) of soft x-ray absorption is a powerful tool to study magnetic and electronic states of ferromagnetic and ferrimagnetic materials. At BL25SU, helicity switching of circularly polarized radiation performed by the twin helical undulators are used for MCD measurements. Two absorption spectra corresponding to an MCD are measured by one energy scan switching the helicity at each energy point. The helicity-switching method is effective for precise measurements. The switching frequency is currently 1 Hz.
  Samples are magnetized by a water-cooled type electromagnet equipped with double yorks. The electromagnet generates variable magnetic field up to 1.9 T at the sample position. Sample temperature can be controlled from 20 K to 300 K. Absorption intensity is measured by means of the total electron yield. A combination of the helicity switching technique and the apparatus provides element specific magnetic hysteresis (ESMH) measurements.

Fig.1 Schematic drawing of a UHV measurement chamber equipped with an electromagnet. The iron sub-pole-pieces are stuck into the chamber, where the vacuum is shielded by welding.

Fig.2 Example of measured MCD spectra and the element specific magnetic hysteresis loops. (a) SXMCD and absorption spectra at the Tb M_4,5-, Fe L_2,3- and Co L_2,3-edges in the Tb₁₈Fe_65.3Co_16.7 film at room temperature. Open circles with solid line correspond to SXMCD spectra. Solid and broken lines represent absorption spectra for the plus and minus helicity of incident photon, respectively. Magnetic filed of 1.9 T was applied so as to be perpendicular with respect to sample surface. (b) ESMH loops recorded at the Tb M₅-, Fe L₃- and Co L₃-edges tuning photon energies to those which give maximum intensity of MCD signals. Solid and open circles correspond to the points measured with decreasing and increasing magnetic fields, respectively.