Intrinsic anomalous Hall effect in thin films of topological kagome ferromagnet Fe3Sn2

Kagomé lattice compounds and their related systems

The search for new Kagomé lattice compounds and their related systems has attracted much interest but is still a great challenge, because these compounds usually show unique structural features and various unusual magnetic properties, but an ideal lattice is not easily obtained and some of the magnetic properties are not well understood. In this feature article review, we summarize the works of our research group in recent years, mainly including new types of lattices, structural features, and the magnetic behaviors of such Kagomé related systems. Moreover, current problems and future prospects of this respect are also discussed.

Transformation of Kagomé and Breathing Kagomé Lattices Induced by Ion Replacement

PbOCu3(SeO3)2(NO3)(OH) was synthesized by means of a replacement of (OH)- groups for F- ions of PbOCu3(SeO3)2(NO3)F, showing a transformation of kagomé and breathing kagomé lattices. Such a replacement did not change their intralayer ferromagnetic interactions and interlayer antiferromagnetic (AFM) interactions but slightly affected the Néel temperature and critical field, where PbOCu3(SeO3)2(NO3)(OH) possesses an AFM ordering at TN = 29.3 K, and a field-induced metamagnetic transition can occur at 2 K while a critical magnetic field of 1.45 T is applied.

Two new tellurite compounds ACu3Te2O8 (A = Ca, Cd) with ferromagnetic spin-1/2 kagomé layers

Two new tellurite compounds ACu3Te2O8 (A = Ca, Cd) have been synthesized by a typical hydrothermal method, exhibiting a similar 2D layered structure in the trigonal system of space group R3̄m, where Cu2+ ions construct a spin-1/2 regular kagomé lattice via corner-sharing. Magnetic measurements confirmed that ACu3Te2O8 (A = Ca, Cd) possesses antiferromagnetic ordering at low temperature, while exchange interactions between magnetic ions within layers are ferromagnetic.

Two-Dimensional Ultrathin Fe3Sn2 Kagome Metal with Defect-Dependent Magnetic Property

Two-dimensional (2D) Fe3Sn2, which is a room-temperature ferromagnetic kagome metal, has potential applications in spintronic devices. However, the systematic synthesis and magnetic study of 2D Fe3Sn2 single crystals have rarely been reported. Here we have synthesized 2D hexagonal and triangular Fe3Sn2 nanosheets by controlling the amount of FeCl2 precursors in the chemical vapor deposition (CVD) method. It is found that the hexagonal Fe3Sn2 nanosheets exist with Fe vacancy defects and show no obvious coercivity. While the triangular Fe3Sn2 nanosheet has obvious hysteresis loops at room temperature, its coercivity first increases and then remains stable with an increase in temperature, which should result from the competition of the thermal activation mechanism and spin direction rotation mechanism. A first-principles calculation study shows that the Fe vacancy defects in Fe3Sn2 can increase the distances between Fe atoms and weaken the ferromagnetism of Fe3Sn2. The resulting 2D Fe3Sn2 nanosheets provide a new choice for spintronic devices.

Magnetodynamic properties of ultrathin films of Fe[Formula: see text]Sn[Formula: see text]-a topological kagome ferromagnet

Fe[Formula: see text]Sn[Formula: see text] is a topological kagome ferromagnet that possesses numerous Weyl points close to the Fermi energy, which can manifest various unique transport phenomena such as chiral anomaly, anomalous Hall effect, and giant magnetoresistance. However, the magnetodynamic properties of Fe[Formula: see text]Sn[Formula: see text] have not yet been explored. Here, we report, for the first time, the measurements of the intrinsic Gilbert damping constant ([Formula: see text]), and the effective spin mixing conductance (g[Formula: see text]) of Pt/Fe[Formula: see text]Sn[Formula: see text] bilayers for Fe[Formula: see text]Sn[Formula: see text] thicknesses down to 2 nm, for which [Formula: see text] is [Formula: see text], and g[Formula: see text] is [Formula: see text]. The films have a high saturation magnetization, [Formula: see text], and large anomalous Hall coefficient, [Formula: see text]. The large values of g[Formula: see text], together with the topological properties of Fe[Formula: see text]Sn[Formula: see text], make Fe[Formula: see text]Sn[Formula: see text]/Pt bilayers useful heterostructures for the study of topological spintronic devices.

Intrinsically dominated anomalous Hall effect in pulsed laser deposited epitaxial Co2MnGe ferromagnetic full Heusler alloy thin films

Large size epitaxial thin films of ferromagnetic Co2MnGe full Heusler alloy are grown over MgO(100) substrate by using pulsed laser deposition technique under optimized growth conditions. Metallic behavior is confirmed from the longitudinal resistivity-temperature data, while a minimum in the resistivity at ∼25 K is attributed to the disorder-induced weak localization effect. Importantly, a dominating intrinsic anomalous Hall conductivity value of ∼21 S cm-1 against an overall anomalous Hall conductivity value of ∼36 S cm-1 at the room temperature has been estimated for the epitaxial Co2MnGe film. The dominating intrinsic mechanism is also evident from the near temperature-independent behavior of the overall anomalous Hall conductivity.

A 2D heavy fermion CePb3 kagome material on silicon: emergence of unique spin polarized states for spintronics

We report on the successful synthesis of a 2D atomically thin heavy-fermion CePb₃ kagome compound on a Si(111) surface. Growth and morphology were controlled and characterized through scanning tunneling microscopy observations revealing the high crystalline quality of the sample. Angle-resolved photoelectron spectroscopy measurements revealed the giant highly-anisotropic Rashba-like spin splitting of the surface states and semi-metallic character of the spectrum. According to the DFT calculations, the occupied hole and unoccupied electron states with huge spin-orbit splitting and out-of-plane spin polarization reside at the M̄ points near the Fermi level E_F, which is ≈100 meV above the experimental one. The out-of-plane FM magnetization was found to be preferred with Ce spin and orbital magnetic momenta values of 0.895μ_B and -0.840μ_B, respectively. The spin-split states near E_F are primarily formed by Pb p_xy orbitals with the admixing of Ce d and f electrons due to the Ce f-d hybridization acquired asymmetry with respect to the sign of k_∥. The observed electronic structure of the CePb₃/Si(111)√3 × √3 system is rather unique and in the hole-doped state, like in our experiment, can be enabled in the tunable spin current regime, which makes it a prospective 2D material for spintronic applications.