Field dependence of the magnetic quantum phase transition in MnSi

Abstract

The dependence on pressure (P ) and field (H ) of the magnetic phase diagram of MnSi has been investigated by means of measurements of the AC susceptibility (χ ) up to 16 kbar and 7 T at temperatures down to 30 mK. For ambient pressure, we report on a peak in χ above T c at a characteristic temperature T m that rises quickly with field. The pressure dependence of T m is found to be strongly analogous to that of the zero-field transition to long-range order at T c . Features of χ in the field versus temperature (T ) phase diagram may be viewed as 'fingerprint' evidence of a field-induced crossover at T m of the itinerant magnetism from a non-polarized regime at high T and low H to a polarized regime at low T and high H . The long-wavelength spin spiral, present at low H , appears to be supported only in the polarized regime, so in the immediate vicinity of the critical pressure P c for which T c → 0, a small pocket exists as a re-entrant state.

Confinement of chiral magnetic modulations in the precursor region of FeGe

“…figure 2) and the calculated χ(H) dependence ( figure 7(c)). Experimentally the characteristic U-shaped anomaly in χ ac (H) indicating the A-phase area has also been observed in MnSi [27,30], Mn 1−y Co y Si and Mn 1−z Fe z Si [8]. These observed anomalies are very similar to the calculated functions χ(H) shown in figure 7(c) which correspond to the hexagonal Skyrmion lattice.…”

“…Nevertheless, these studies have accumulated an impressive database on peculiarities of magnetic properties in this enigmatic area. Together with earlier observations [22,24,25,26,27,29,30] and recent theoretical findings [10,47,48] the following important conclusions about the physical nature of the precursor region can be drawn: (i) It consists of a multiplicity of modulated states which have complex multi-dimensional textures, and (ii) precursor states are fundamentally different from regular chiral modulations, as theoretically motivated in [10,48].…”

“…The sense of the magnetization rotation is fixed due to the presence of the chiral DzyaloshinskiiMoriya (DM) interaction [20,21]. However, in their magnetic field−temperature, (H, T ), phase diagrams, as sketched in figure 1(a), numerous puzzling physical anomalies have been observed in a narrow temperature interval in the vicinity of T C [8,10,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42]. The origin of these "precursor anomalies" (hatched area in figure 1(a)) and notably the magnetic structure of the so-called A phase is a long-standing and intriguing problem in chiral magnetism.…”

Non-Fermi Liquid Regimes and Superconductivity in the Low Temperature Phase Diagrams of Strongly Correlated d- and f-Electron Materials

“…AC magnetic susceptibility measurements on high purity single crystals demonstrated that the magnetic phase transition at T C changes from second order to first order at P ≈ 12 kbar. Additionally the existence of itinerant metamagnetism corroborates the presence of a local minimum in the free energy [178,179].…”

“…[29]. Here ρ and χ indicate that the helical ordering temperature T c was determined by measurements of the electrical resistivity [171] and magnetic susceptibility [178,179], respectively. ENS denotes elastic neutron scattering [180] that identified the cross-over temperature scale T 0 to the partial order.…”