RESUMEN
Helimagnetic structures, in which the magnetic moments are spirally ordered, host an internal degree of freedom called chirality corresponding to the handedness of the helix. The chirality seems quite robust against disturbances and is therefore promising for next-generation magnetic memory. While the chirality control was recently achieved by the magnetic field sweep with the application of an electric current at low temperature in a conducting helimagnet, problems such as low working temperature and cumbersome control and detection methods have to be solved in practical applications. Here we show chirality switching by electric current pulses at room temperature in a thin-film MnAu2 helimagnetic conductor. Moreover, we have succeeded in detecting the chirality at zero magnetic fields by means of simple transverse resistance measurement utilizing the spin Berry phase in a bilayer device composed of MnAu2 and a spin Hall material Pt. These results may pave the way to helimagnet-based spintronics.
RESUMEN
Breaking of spatial inversion symmetry induces unique phenomena in condensed matter. In particular, by combining this symmetry with magnetic fields or another type of time-reversal symmetry breaking, noncentrosymmetric materials can be made to exhibit nonreciprocal responses, which are responses that differ for rightward and leftward stimuli. However, the effect of spatial inversion symmetry breaking on thermal transport in uniform media remains to be elucidated. Here, we show nonreciprocal thermal transport in the multiferroic helimagnet TbMnO3 The longitudinal thermal conductivity depends on whether the thermal current is parallel or antiparallel to the vector product of the electric polarization and magnetization. This phenomenon is thermal rectification that is controllable with external fields in a uniform crystal. This discovery may pave the way to thermal diodes with controllability and scalability.
RESUMEN
Magneto-piezoelectric effect (MPE) refers to generation of strain in response to electric currents in magnetic metals which lack both time-reversal and space-inversion symmetries. A recent experimental paper demonstrated the MPE in the antiferromagnetic metal EuMnBi2 at 77 K, but the limited temperature range of the MPE measurement hampered detailed discussion on the MPE. Here we extend the measurement temperature range down to liquid He temperature, and studied the dependences of the MPE on the laser position, frequency and amplitude of electric currents, and temperature in the very low temperature range. We show that the MPE signal is enhanced at low temperatures and reaches a maximum magnitude in the antiferromagnetically ordered states of both Eu and Mn ions. An effective piezoelectric coefficient for the MPE at 4.5 K is estimated to be as large as 3500 pC/N, which is much larger than piezoelectric coefficients of typical piezoelectric ceramics, although the magnitude of real MPE displacements should be limited due to strong Joule heating at high electric currents. The present results may open up a new strategy to realize new lead-free piezoelectric materials.
RESUMEN
For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm(2)/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials.