BL practice at BL25SU
10/23/2009, ver.1, T.Nakamura and T. Ohkochi

Program of BL practice
We, at the BL25SU, plan MCD spectra measurements and Photoelectron emission microscopy(PEEM) experiment, on 9th. and 10th. of Nov, respectively. So, menus of the practice are difference
between the first and the second days.

Outline of BL25SU
BL25SU is designed for research on electronic structures, magnetic states and surface
structures of solids with high energy-resolution circularly-polarized soft x-rays.

Left- andright-handed circularly polarized radiation is obtained along the same optical axis by twin helicalundulators. The helicity of the circularly polarized radiation can be periodically switched at 0.1, 1 or
10 Hz by using kicker magnets distributed around the two undulators. The beamline monochromatoris a constant deviation type with varied line-spacing plane gratings covering an energy region of 0.22
∼ 2 keV. The resolving power of the monochromator is more than 10,000 in the whole energy region.
Four kinds of spectroscopic techniques are available for public use: high energy-resolution
photoemission spectroscopy, magnetic circular dichroism of core absorption, two-dimensional
angular distributions of photoelectrons, photoelectron emission microscope. Measurements areperformed in ultra high vacuum conditions down to 10-8 Pa.

Fig.1 Layouts of beamline optics at BL25SU. MCD apparatus is installed as astation-4 (ST4) downstream of the ST3.

Time schedule of 9th, Nov.
9:00-

Introduction of beamline design and major scientific activities.

10:00-

Sample preparation and introduction to a load lock chamber.

10:30-

Introduction of the helicity switching and MCD data acquisition techniques.

11:30-

Measurement of beam properties under helicity switching in the 1 Hz mode.

12:30-------- Lunch -----------

13:30-MCD measurements (Spectra and hysteresis loops). I propose having a time for exchangesof scientific interests and discussion on some technical subjects during the measurements.

16:00-Up to participant’s interests and requests.

-17:00Close

X-ray magnetic circular dichroism
Magnetic circular dichroism (MCD) of soft x-ray absorption is a powerful tool to study magneticand electronic states of ferromagnetic and ferrimagnetic materials. At BL25SU, helicity switching ofcircularly 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 scanswitching 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 10 K to 300 K and from 300 K to 550 K. Absorption intensity ismeasured by means of the total electron yield. A combination of the helicity switching technique andthe apparatus provides element specific magnetic hysteresis (ESMH) measurements.

Time schedule (PEEM) of 10th, Nov.
9:00- Explanation of photoemission electron microscopy (PEEM) device.
10:00- Sample preparation, introduction to a chamber, surface cleaning.
12:00- ---------- Lunch ---------13:00- Measurement (magnetic domain images and X-ray absorption/magnetic dichroism spectra ofselected areas)
16:00- Free discussion-17:00 Close

Photoemission electron microscope (PEEM)
Photoemission electron microscope (PEEM) has been of great benefit in the field of surface science.
The PEEM device in BL25SU (PEEMSPECTOR) provides the spatial distribution of photoemission
electron with the resolution below 100 nanometers. The emitted electrons are primarily magnified by
the large difference in electric field between sample and objection lens, and three projection lenses
produce the final magnified image on the screen. The photoelectron intensity emitted from thesurface is proportional to the x-ray absorption intensity, so that the chemical composition map ofspecific element can be obtained by this method. Especially, a combination technique with circularly
polarized X-rays enables us to visualize a magnetic domain image, making use of magnetic circulardichroism (MCD) or magnetic linear dichroism (MLD) effect. The X-ray absorption and/or MCD
spectra at specific areas are also available by taking the images successively, sweeping X-ray energy
near the absorption edge. In this practice, we will demonstrate the observation of magnetic domains(XMCD-PEEM images) of some magnetic materials, i.e. Fe single crystal or patterned magneticmedia.