New magnetic intermediate state, “B-phase,” in the cubic chiral magnet MnSi
M. Ohkuma,
M. Mito,
M. Pardo,
Y. Kousaka,
S. Iwasaki,
K. Ohishi,
J. Akimitsu,
K. Inoue,
V. Laliena,
J. Campo
Affiliations
M. Ohkuma
Graduate School of Engineering, Kyushu Institute of Technology, Kitakyushu 804-8550, Japan
M. Mito
Graduate School of Engineering, Kyushu Institute of Technology, Kitakyushu 804-8550, Japan
M. Pardo
Aragón Nanoscience and Materials Institute (CSIC–University of Zaragoza) and Physics Condensed Matter Department, Science Faculty, C/ Pedro Cerbuna 12, 50009 Zaragoza, Spain
Y. Kousaka
Chirality Research Center, Hiroshima University, Higashihiroshima 739-8526, Japan
S. Iwasaki
Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan
K. Ohishi
Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society (CROSS), Tokai, Ibaraki 319-1106, Japan
J. Akimitsu
Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan
K. Inoue
Chirality Research Center, Hiroshima University, Higashihiroshima 739-8526, Japan
V. Laliena
Department of Applied Mathematics, University of Zaragoza, C/ María de Luna 3, 50018 Zaragoza, Spain
J. Campo
Chirality Research Center, Hiroshima University, Higashihiroshima 739-8526, Japan
It is well known that the archetype chiral magnet MnSi stabilizes a skyrmion lattice, termed “A-phase,” in a narrow temperature range in the vicinity of the paramagnetic boundary around Tc ∼ 29 K and Hc ∼ 2 kOe. Recently, it has been predicted that at much lower temperatures below Tc, the conical helicoid and the forced ferromagnetic (FFM) states could be separated by a new “unknown state.” In order to detect this “unknown state,” we explored the phase diagram of MnSi oriented single crystals as a function of the d.c. magnetic field (H⃗dc) and the temperature (T) by using a.c. magnetization measurements. For H⃗dc∥ 〈111〉, we observed a new region, termed “B-phase,” in the magnetic phase diagram, characterized by a flat-valley-like anomaly on the in-phase component of the a.c. magnetization (m′), over 3.5 ≤ Hdc ≤ 6.2 kOe just below the low temperature (T < 6 K) FFM boundary. The observed frequency independence over 0.3–1000 Hz and the absence of any measurable absorption in the a.c. magnetization (m″) in the “B-phase” suggest a static nature. The “B-phase” was not observed for either H⃗dc∥ 〈100〉 or 〈110〉, revealing that the magnetic anisotropy could play a role in the stabilization of the phase. The “B-phase” could be compatible with the theoretical predictions if the new magnetic state is supposedly related with a relative reorientation of the four helices in MnSi.
