New magnetic intermediate state, “B-phase,” in the cubic chiral magnet MnSi

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 T c ∼ 29 K and H c ∼ 2 kOe. Recently, it has been predicted that at much lower temperatures below T c , 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 [Formula: see text] and the temperature ( T) by using a.c. magnetization measurements. For [Formula: see text] 〈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 ≤ H dc ≤ 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 [Formula: see text] 〈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.