Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

1A, 16A2/2003S1-001, 2004G-051

Magnetoelectric X-ray Scattering in GaFeO3 and Fe3O4
1Masakazu MATSUBARA*1, Jong-Hoon3 JUNG2, Yoshiaki SHIMADA, Taka-hisa ARIMA2,
1
Hiroshi SAWA , and Yoshinori TOKURA
1
DepartmentofApplied
Physics, University of Tokyo, Tokyo 113-8656, Japan
2
ERATO-JST,c/o
AIST, Tsukuba, Ibaraki 305-8562, Japan
3
KEK-PF, Tsukuba, Ibaraki 305-0801, Japan

Introduction
The linear magnetoelectric (ME) effect can be observedin magnetically ordered crystals whose magnetic groupdoes not contain the space inversion operation, i.e., wheretime reversal R and space inversion I operations arebroken simultaneously. In optical or x-ray region, thenovel nonreciprocal magneto-optical phenomena, termedmagnetochiral or optical ME effect, are expected to show
up in such a crystal as characterized by a different opticalresponse (absorption or refraction) depending on lightpropagation direction k. Spectroscopy of thisnonreciprocal effect is important to clarify the
microscopic mechanism of the ME effect which isattracting renewed interest also from the viewpoint of theapplication to spin-electronics.
In this study, we have investigated resonant ME x-rayscattering (MEXS) in a polar ferrimagnet GaFeO3 and aspinel-type ferrimagnet Fe3O4. Here, we propose that
present element-specific resonant MEXS would be aunique probe of the magnetic state with broken
centrosymmetry.
Experimental
The samples used in this work were GaFeO3 and Fe3O4
single crystals grown by a floating-zone method. The
measurements of magnetic x-ray scattering were carriedout at BL-1A and 16A2. An incident beam was injectedon the (010) and (111) surface for GaFeO3 and Fe3O4,
respectively, and a modulated magnetic field was applied
perpendicular to the incident beam, namely in Voigt
configuration. The modulated magnetic and/or ME
scattering intensity ∆I(f) was recorded as the ratio of spindependent to spin-independent scattering intensity ∆I(f)/Iwith a lock-in amplifier.
Results and Discussions
First, we describe the results in a polar ferrimagnet
GaFeO3. For the (020) and (040) Bragg reflections, wehave observed a change in the scattering intensity withreversal of the magnetization direction near the Fe K preedge [1]. In Fig. 1, we show the magnetic-field
modulation spectra ∆I(f)/I for the (020) and (040) Braggreflections, respectively. One can see a large energyindependent component for (020) and resonant peaks forboth reflections. The energy-independent component is
assigned to the well-known conventional magnetic x-ray
scattering (MXS) from the viewpoint of the spin structureof GaFeO3. On the other hand, the resonant signal near136

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the pre-edge is possibly related to MEXS, which issensitive not only to the magnetism but also to thebreaking of the inversion symmetry [2]. Actually, we
certainly observed, that the MEXS signal is reversed insign when the sample (spontaneous polarization) wasreversed, which evidences our expectation (Fig. 1).

Figure 1: Magnetic field modulation spectra of Braggreflections at 50 K for (020) (open circles), (040)(solid circles), and (040) (open squares). The
absorption spectrum around the Fe K-absorption edgeof GaFeO3 is also shown by a solid line.
Next, we describe the results of a spinel-typeferrimagnet Fe3O4. Although I symmetry is globallyrestored, it is locally broken at the tetrahedral A site. It ispossible to detect the local ME scattering at
noncentrosymmetric site as the nonreciprocal effect, due
to the possibility of adjusting phase factors, even insystems where the I symmetry is globally restored. At the(222) Bragg reflection with a specific structure factor, infact, resonant magnetic component was observed aroundthe pre-edge region of Fe K-absorption. As comparedwith the (333) and (444) Bragg reflections, we deduced
that the resonant structure observed at the (222) Braggreflection is due to MEXS at the spinel A site with locallybroken inversion symmetry (Td).
References[1] T. Arima, J. H. Jung, M. Matsubara, M. Kubota, J. P.
He, Y. Kaneko, and Y. Tokura, J. Phys. Soc. Jpn. 74, 1419
(2005).
[2] M. Kubota, T. Arima, Y. Kaneko, J. P. He, X. Z. Yu,
and Y. Tokura, Phys. Rev. Lett. 92, 137401 (2004).
* m-matsubara@aist.go.jp