Photon Factory Activity Report 2005 #23 Part B (2006)
Materials Science

16A2/2004G235

Magnetic Correlation of HoB4 with Geometrical Frustration
Takeshi MATSUMURA*, Daisuke OKUYAMA, Hironori NAKAO, Youichi MURAKAMI
Department of Physics, Tohoku University, Sendai 980-8578, Japan

1000

8.06

8.08

Energy [keV]

Users' Report

HoB4 (100)σ−π'E=8.072 keV
T=2.8 K
T=9.0 K

Ψ=92°

Ψ=6°

10

Ψ=6°

8.10

200

5.5
θ [deg]

1000
8.04

5.0

6.0

6.5

6.5

7.0

7.5

8.0

θ [deg]Figure 2: Peak profile of the resonant scattering for the(1 0 0) reflection at two azimuthal angles. Solid lines are
the resolution functions expected from the (2 0 0)
fundamental reflection.
8.06

8.08

8.10

Energy [keV]

Figure 1: X-ray energy dependences of the resonant
scattering intensity for the (1 0 0) reflection of HoB4 at
two azimuthal angles near 0° and 90°.

116

100

15000
8.04

1000

300

Ψ=92°

HoB4 (100)σ−π'T=2.8 K
T=9.0 K

Intensity [cps]Intensity [cps]Results, Analysis, and Discussion
Resonant x-ray scattering experiment has been
performed at BL16A2 using a liquid He cryostat and the(1 0 0) forbidden reflection has been investigated in detail.
Polarization analysis was carried out because themagnetic scattering arises on the σ-π’ process. Azimuthal
angle is defined to be zero when the c-axis is parallel tothe scattering plane. Measurements were performed
below TN2 and in the paramagnetic phase above TN1.
Figure 1 shows the energy dependence of the intensity ofthe (1 0 0) reflection. Strong magnetic reflection wasobserved at around Ψ=90°, while it was weak aroundΨ=0°. This result is opposite to DyB4, where the intensity
was strong at around Ψ=0° and weak around Ψ=90°. At
T=9.0K and Ψ=6° is the ATS scattering due to theanisotropy of the local symmetry of Ho.

Figure 2 shows the peak profiles of these resonantpeaks at E=8.072 keV, which corresponds to the energy
for the E1 transition process. The profiles are slightly
broader than the resolution only in the region of the tails.
When we analyze the peak shape in detail, the peak
profile at Ψ=92° can be well fitted with a Lorentzian.
Although the profile at Ψ=6° is not symmetric because of
the crystalline mosaic, it may also be regarded as aLorentzian. A similar broadening was also observed inneutron diffraction, which we consider to be due to ashort-ranged domain structure of the magnetic structure
within the c-plane. The reason that the intensity at Ψ=90°
is much stronger than that at Ψ=0° may be that the cplane magnetic component in HoB4 is much larger thanthat of DyB4.
In the intermediate phase of DyB4, the peak profile at
Ψ=90° was apparently borader than the resolution, whilethat at Ψ=0° was as sharp as the resolution. We haveinterpreted the result by comparing with a model
calculation that the resonance at Ψ=90° is due to themagnetic component within the c-plane or the <Ozx>type quadrupolar moment. However, in HoB4, since thesystem enters into the ordered phase with lattice
distortion through a first-order transition, no suchbroadening is observed as in DyB4 that reflect thefluctuating quadrupolar moments.

Intensity [cps]Introduction
A tetragonal rare-earth compound system of RB4 has
been attracting growing interest as a system where boththe quadrupolar and magnetic degrees of freedom areactive in the geometrically frustrated lattice, which isequivalent to the Shastry-Sutherland lattice. We reported
on the short-ranged magnetic correlation in DyB4 last year.
We observed a broadened peak profile of the resonant xray scattering from DyB4 in the intermediate phase where
the quadrupolar moments are considered to be fluctuating[1]. In order to compare the result with HoB4, whichexhibits similar phase transitons as in DyB4 at TN1=7.5 K
and at TN2=5.9 K, we have performed resonant x-rayscattering experiment on HoB4. It has already been
established by neutron diffraction that an incommensurate
magnetic order takes place at TN1 and a first-order-like
phase transition at TN2 into a commensurate structure
described by q=(100).

References[1] D. Okuyama et al., J. Phys. Soc. Jpn., 74, 2434 (2005).
* tmatsu@iiyo.phys.tohoku.ac.jp