ABSTRACT
The interplay of magnetism and spin-orbit coupling on an Fe kagome lattice in Fe3Sn2 crystal produces a unique band structure leading to an order of magnitude larger anomalous Hall effect than in conventional ferromagnetic metals. In this work, we demonstrate that Fe-Sn nanocrystalline films also exhibit a large anomalous Hall effect, being applicable to magnetic sensors that satisfy both high sensitivity and thermal stability. In the films prepared by a co-sputtering technique at room temperature, the partial development of crystalline lattice order appears as nanocrystals of the Fe-Sn kagome layer. The tangent of Hall angle, the ratio of Hall resistivity to longitudinal resistivity, is maximized in the optimal alloy composition of close to Fe3Sn2, implying the possible contribution of the kagome origin even though the films are composed of nanocrystal and amorphous-like domains. These ferromagnetic Fe-Sn films possess great advantages as a Hall sensor over semiconductors in thermal stability owing to the weak temperature dependence of the anomalous Hall responses. Moreover, the room-temperature fabrication enables us to develop a mechanically flexible Hall sensor on an organic substrate. These demonstrations manifest the potential of ferromagnetic kagome metals as untapped reservoir for designing new functional devices.
ABSTRACT
Quantum states characterized by nontrivial topology produce interesting electrodynamics and versatile electronic functionalities. One source for such remarkable phenomena is emergent electromagnetic field, which is the outcome of interplay between topological spin structures with scalar spin chirality and conduction electrons. However, it has scarcely been exploited for emergent function related to heat-electricity conversion. Here we report an unusually enhanced thermopower by application of magnetic field in MnGe hosting topological spin textures. By considering all conceivable origins through quantitative investigations of electronic structures and properties, a possible origin of large magneto-thermopower is assigned to the strong energy dependence of charge-transport lifetime caused by unconventional carrier scattering via the dynamics of emergent magnetic field. Furthermore, high-magnetic-field measurements corroborate the presence of residual magnetic fluctuations even in the nominally ferromagnetic region, leading to a subsisting behavior of field-enhanced thermopower. The present finding may pave a way for thermoelectric function of topological magnets.
ABSTRACT
We investigate magnetotransport properties in a single crystal of pyrochore-type Nd2Ir2O7. The metallic conduction is observed on the antiferromagnetic domain walls of the all-in-all-out-type Ir 5d moment ordered insulating bulk state that can be finely controlled by an external magnetic field along [111]. On the other hand, an applied field along [001] induces the bulk phase transition from insulator to semimetal as a consequence of the field-induced modification of the Nd 4f and Ir 5d moment configurations. A theoretical calculation consistently describing the experimentally observed features suggests a variety of exotic topological states as functions of electron correlation and Ir 5d moment orders, which can be finely tuned by the choice of rare-earth ion and magnetic field, respectively.