Photon Factory Activity Report 2018 #36 (2019)

BL-10A/2014G534

Eﬀects of a strong gravity on YMnO3 single crystal
Makoto TOKUDA1,2, Akira YOSHIASA1,* Kazumasa SUGIYAMA2 and Tsutomu MASHIMO1
1
Institute of Pulsed Power Science, Kumamoto University, Kumamoto, 860-8555, Japan
2
Institute for Materials Research, Tohoku Univ. Sendai 980-8577, Japan
1 Introduction
Hexagonal manganites RMnO3 (R is a rare earthelement) crystallize in a hexagonal structure (spacegroup: P63cm) if the ionic radius of R is small (R=Ho-Lu,Y, and Sc). These compounds have attracted attention
because they exhibit multiferroic eﬀects. The crystal andmagnetic structures of these compounds have been
investigated to assess their possible applications inelectronics.
Similar to magnetic and electric ﬁelds, gravity is aﬁeld state variable that acts directly on atoms in materials
through a body force, whereas pressure and temperature
are thermodynamic variables that aﬀect atoms
statistically. Unique uniaxially distorted crystalline state
can induce structural changes in compounds other thanthose caused by high pressure and high temperature,
thereby allowing the formation of a unique metastablephase. In the present study, we investigated the detailed
relationships between the changes in the structure andmagnetic properties of the YMnO3 single crystal
quenched in a strong gravitational ﬁeld [1].

neighbor Mn-Mn and Mn-O bond distances, thereby
demonstrating that trimerization distortion occurred in theab plane under the strong gravitational ﬁeld (Fig.2).
Raman spectroscopy measurements showed that theRaman peaks for the gravity sample included a new
Raman line at 178cm−1, which has never been reported inprevious experimental studies. Magnetic measurements
indicated that there were changes in the magnetic
anisotropy, which were explained by changes in the spin–orbit interaction due to lattice distortion.

Fig. 1: Schematic showing the displacement of the atoms along
the c-axis after the strong-gravity experiments [1].

2 Experiment
A single crystal of YMnO3 was grown in a desktoptype furnace using the ﬂoating-zone method. The
direction of the gravitational ﬁeld was perpendicular to
the Si3N4 plate and parallel to the [0001] plane of thesample. At a rotational velocity of 140000rpm, thegravitational force on the sample was 0.78×106G in avacuum. The rotor was heated to 400°C using a hollow
carbon cylinder, which was heated by a high-frequency
heating system. Toward the end of this procedure, thesample was quenched to room temperature and therotation was stopped within about 5min.
Crystallographic data were determined a four-circle
diffractometer using synchrotron radiation at beamline
BL-10A of PF, KEK. The structure was solved by direct
methods and reﬁned using a full-matrix least squares
procedure in the SHELXL reﬁnement package using
least-squares minimization.
3 Results and Discussion
Under strong gravitational ﬁelds, the uniqueuniaxially distorted crystalline state induces structuralchanges in compounds other than those caused by highpressure and high temperature [1]. We determined thechanges in the crystalline structure and physicalproperties of the metastable YMnO3 quenched in thestrong gravitational ﬁeld (Fig. 1). According to fourcircle single-crystal X-ray diﬀraction data, the structural
analyses indicated changes in the inequivalent nearest-Fig. 2: Schematics illustrating the formation of the Mn-trimer in
the ab-plane for the initial (a) and gravity (b) samples. The Mn
trimers in the initial sample were connected with each otherorganically over the ab-plane, whereas each Mn trimer wasisolated in the gravity sample [1].

References[1] M. Tokuda et al., J. Phys. Chem. Solids, 129, 172(2019) https://doi.org/10.1016/j.jpcs.2018.12.023* yoshiasa@kumamoto-u.ac.jp