Unique helical magnetic order and field-induced phase in trillium lattice antiferromagnet EuPtSi

トリリウム格子反強磁性体EuPtSiにおける特異なヘリカル磁気秩序と磁場誘起相

金子 耕士   ; Frontzek, M. D.*; 松田 雅昌*; 中尾 朗子*; 宗像 孝司*; 大原 高志   ; 垣花 将司*; 芳賀 芳範   ; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*

Kaneko, Koji; Frontzek, M. D.*; Matsuda, Masaaki*; Nakao, Akiko*; Munakata, Koji*; Ohara, Takashi; Kakihana, Masashi*; Haga, Yoshinori; Hedo, Masato*; Nakama, Takao*; Onuki, Yoshichika*

Magnetic transitions in chiral antiferromagnet EuPtSi were investigated by means of single crystal neutron diffraction. In the ground state, magnetic peaks emerge at positions represented by =. Upon heating, an additional magnetic peak splitting around 2.5 K was uncovered, indicating a presence of a first-order transition with =. An half-polarized neutron scattering for polarization parallel to Q reveled that polarization antiparallel to Q has stronger intensity in both magnetic phases. This feature clarifies single chiral character of helical structure with moments normal to the ordering vector in both ordered states. Under vertical magnetic field along [1,1,1] in the phase, magnetic peaks form hexagonal patterns in the equatorial scattering plane around nuclear. An ordering vector of the -phase has the similar size in the periodicity to , and could be a hallmark of a formation of skyrmion lattice in EuPtSi.