Stress-induced magnetic textures and fluctuating chiral phase in MnGe chiral magnet

Abstract

International audienceWe have studied the MnGe chiral magnet below T N = 170 K, by magnetic measurements, Mössbauer spectroscopy, and by neutron diffraction at ambient and under nonhydrostatic pressure. At ambient pressure, we observe the coexistence of two magnetic phases belonging to the same crystal phase in a large temperature range (down to 100 K) below T N : ferromagnetically correlated rapidly fluctuating spins coexist with frozen spins involved in the helical order. Applying a uniaxial pressure component induces a strong magnetic texture, where most of the helical axes reorient along the stress axis. The magnetic texture persists in the fluctuating chiral state up to T N. Our results suggest that the zero field ground state at ambient pressure is a multidomain state consisting of helical domains with random orientations rather than a three-dimensional skyrmion lattice. They show the presence of an unusually broad transition to paramagnetism with a dynamical phase separation triggered by temperature

Thermal expansion of monogermanides of 3d-metals

“…The evolution of CT E on cooling indicates a gradual change in the average fraction of high spin state. However, according to susceptibility and neutron scattering data the conversion is not complete even at very low temperatures [7,8,16]. Such a scenario assumes that ferromagnetic droplets observed with neutron scattering should be associated with regions enriched with high spin states.…”

“…First, in spite of larger Mn-Mn separation, the magnetic ordering temperature is much higher (T MnGe c ≈ 170 K and T MnSi c ≈ 29 K for MnSi) [6][7][8]. Second, small angle neutron scattering revealed an intricate ordering scenario comprising new ferromagnetic phase between 150 and 300 K not met for MnSi [6].…”

Complex magnetic phase diagram and skyrmion lifetime in an ultrathin film from atomistic simulations

“…We note that the FD region in this system is significantly wider (≈ 150 K) than in MnSi (1 − 2 K). Note that a similarly wide transition region has been identified in MnGe at B = 0 T [48,49], though the given interpretation was different. The transition between the FP and the PM phase was obtained similarly from χ (T ), corresponding to the region with the increased number of skyrmions at large magnetic field in Figs.…”

Magnetostriction of helimagnets in the skyrmion crystal phase

“…As a magnetic texture, skyrmion is not only affected by application of electromagnetic fields such as bias magnetic field, electric current [15], and laser [16], but also sensitive to non-electromagnetic fields such as temperature gradient [17] and mechanical stresses [3,18]. While the interaction between skyrmions and the electromagnetic fields or the temperature gradient are well-understood both theoretically and experimentally, the effect of mechanical stress on the skyrmion is not well addressed, even though several previous experiments have proven that mechanical stress is an effective method for controlling the formation and stability of skyrmions [3,[18][19][20][21][22][23][24] and even their dynamic properties [25]. More specifically, the ultra-low emergent elastic stiffness [26] of the skyrmion crystal (SkX) observed in FeGe thin films [3] and in MnSi [18] makes it convenient to manipulate with mechanical stresses.…”