Electrical magnetochiral effect induced by chiral spin fluctuations

Abstract

Chirality of matter can produce unique responses in optics, electricity and magnetism. In particular, magnetic crystals transmit their handedness to the magnetism via antisymmetric exchange interaction of relativistic origin, producing helical spin orders as well as their fluctuations. Here we report for a chiral magnet MnSi that chiral spin fluctuations manifest themselves in the electrical magnetochiral effect, i.e. the nonreciprocal and nonlinear response characterized by the electrical resistance depending on inner product of current and magnetic field. Prominent electrical magnetochiral signals emerge at specific temperature-magnetic field-pressure regions: in the paramagnetic phase just above the helical ordering temperature and in the partially-ordered topological spin state at low temperatures and high pressures, where thermal and quantum spin fluctuations are conspicuous in proximity of classical and quantum phase transitions, respectively. The finding of the asymmetric electron scattering by chiral spin fluctuations may explore new electromagnetic functionality in chiral magnets.

Electric current control of spin helicity in an itinerant helimagnet

“…It should be noted that the magnetic field dependence of ρ 2f asym is contrastive with the linear magnetization curve along the a-axis 16 . Similar sharp enhancement at a low magnetic field unrelated to the magnetization is observed in the paramagnetic state of MnSi 28 , which may be a characteristic of the chiral fluctuation-induced magnetochiral signal. Importantly, the strong chiral fluctuation in the vicinity of the phase boundary should make the magnetic structure electrically susceptible, which should more readily enable controllability of the spin helicity.…”

“…While nonchiral noncentrosymmetric materials also show similar 2nd harmonic resistivities 26,27 , a characteristic feature of the electrical magnetochiral effect is that the nonlinear transport is emergent parallel or antiparallel to the applied magnetic field. Such a phenomenon has been observed in several helimagnets with chiral crystal structures 28,29 . Since it has well been established that ρ ch depends on the chirality, the effect is useful as a prove for the sign of the chirality.…”

“…Figure 4c shows the temperature dependence of ρ 2f asym at 0.4 T. The data clearly show the sharp enhancement of ρ 2f asym at the phase boundary. In helimagnets with noncentrosymmetric crystal structures, the magnetochiral effect has been observed in a wider temperature range 28,29 . In MnSi, the magnetochiral signal shows an enhancement around the helical-paramagnetic transition temperature, but it is suppressed by applying a large magnetic field 28 .…”

“…In helimagnets with noncentrosymmetric crystal structures, the magnetochiral effect has been observed in a wider temperature range 28,29 . In MnSi, the magnetochiral signal shows an enhancement around the helical-paramagnetic transition temperature, but it is suppressed by applying a large magnetic field 28 . The origin of this was ascribed to the chiral magnetic fluctuation in the vicinity of the phase boundary.…”

Phonons Hum a Magnetochiral Tune

“…When both symmetries are simultaneously broken, a nonreciprocal property appears, the so-called magnetochiral effect (MCE). The MCE has been observed for photons [1][2][3][4][5], electrons [6][7][8][9], and magnons [10][11][12]. Here, the (quasi) particles with the propagation vector k parallel and antiparallel to the magnetic field H show different propagation properties.…”