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Register a new userSpin Spiral and Topological Hall Effect in a Metamagnet Fe$_{3}$Ga$_{4}$
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A new mechanism for Topological Hall Effect (THE) was recently proposed for the spiral magnet YMn$_{6}$Sn$_{6},$ which requires transverse conical spiral (TCS) magnetism, induced by external magnetic field, combined with thermally excite helical spiral magnons. In principle, this mechanism should be applicable to other itinerant spiral magnets as well. In this paper, we show that another metamagnetic compound, Fe$_{3}$Ga$_{4}$, where THE was observed experimentally before, in one of its phases satisfies this condition, and the proposed theory of thermal-fluctuation driven THE is quantitatively consistent with the experiment. This finding suggests that this mechanism is indeed rather universal, and the effect may have been observed in other compounds before, but overlooked.
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We report on spin Hall magnetoresistance (SMR) and spin Seebeck effect (SSE) in single crystal of the rare-earth antiferromagnet DyFeO$_{3}$ with a thin Pt film contact. The angular shape and symmetry of the SMR at elevated temperatures reflect the antiferromagnetic order of the Fe$^{3+}$ moments as governed by the Zeeman energy, the magnetocrystalline anisotropy and the Dzyaloshinskii-Moriya interaction. We interpret the observed linear dependence of the signal on the magnetic field strength as evidence for field-induced order of the Dy$^{3+}$ moments up to room temperature. At and below the Morin temperature of 50$,$K, the SMR monitors the spin-reorientation phase transition of Fe$^{3+}$ spins. Below 23$,$K, additional features emerge that persist below 4$,$K, the ordering temperature of the Dy$^{3+}$ magnetic sublattice. We conclude that the combination of SMR and SSE is a simple and efficient tool to study spin reorientation phase transitions and sublattice magnetizations.
Mn$_{3-x}$Ga (x = 0.1, 0.4, 0.7) thin films on MgO and SrTiO$_3$ substrates were investigated with magnetic anisotropy perpendicular to the film plane. An anomalous Hall-effect was observed for the tetragonal distorted lattice in the crystallographic D0$_{22}$ phase. The Hall resistivity $varrho_{xy}$ was measured in a temperature range from 20 to 330 K. The determined skew scattering and side jump coefficients are discussed with regard to the film composition and used substrate and compared to the crystallographic and magnetic properties.
We report the structural, static, and dynamic properties of Cr$_{0.5}$Fe$_{0.5}$Ga by means of powder x-ray diffraction, magnetization, heat capacity, magnetic relaxation, and magnetic memory effect measurements. DC magnetization and AC susceptibility studies reveal a spin-glass transition at around $T_{rm f} simeq 22$~K. An intermediate value of the relative shift in freezing temperature $delta T_{rm f} simeq 0.017$, obtained from the AC susceptibility data reflects the formation of cluster spin-glass states. The frequency dependence of $T_{rm f}$ is also analyzed within the framework of dynamic scaling laws. The analysis using power law yields a time constant for a single spin flip $tau* simeq 1.1times10^{-10}$~s and critical exponent $z u^{prime}=4.2pm0.2$. On the other hand, the Vogel-Fulcher (VF) law yields the time constant for a single spin flip $tau_0 simeq 6.6times10^{-9}$~s, VF temperature $T_{rm 0}=21.1pm0.1$~K, and an activation energy $E_{rm a}/k_{rm B} simeq 16$~K. The value of $tau*$ and $tau_0$ along with a non-zero value of $T_{rm 0}$ provide further evidence for the cluster spin-glass behaviour. The magnetic field dependent $T_{rm f}$ follows the de Almeida-Thouless line with a non-mean-field type instability, reflecting either a different universality class or strong anisotropy in the spin system. A detailed non-equilibrium dynamics study via relaxation and memory effect experiments demonstrates striking memory effects. All the above observations render a cluster spin-glass behaviour which is triggered by magnetic frustration due to competing antiferromagnetic and ferromagnetic interactions and magnetic site disorder. Moreover, the asymmetric response of magnetic relaxation with respect to the change in temperature, below $T_{rm f}$ can be explained by the hierarchical model.
Noncollinear antiferromagnets (AFMs) have recently attracted a lot of attention owing to the potential emergence of exotic spin orders on geometrically frustrated lattices, which can be characterized by corresponding spin chiralities. By performing first-principles density functional calculations together with group-theory analysis and tight-binding modelling, here we systematically study the spin-order dependent anomalous Hall effect (AHE) and magneto-optical effect (MOE) in representative noncollinear AFMs Mn$_{3}X$N ($X$ = Ga, Zn, Ag, and Ni). The symmetry-related tensor shape of the intrinsic anomalous Hall conductivity (IAHC) for different spin orders is determined by analyzing the relevant magnetic point groups. We show that while only the ${xy}$ component of the IAHC tensor is nonzero for right-handed spin chirality, all other elements, $sigma_{xy}$, $sigma_{yz}$, and $sigma_{zx}$, are nonvanishing for a state with left-handed spin chirality owing to lowering of the symmetry. Our tight-binding arguments reveal that the magnitude of IAHC relies on the details of the band structure and that $sigma_{xy}$ is periodically modulated as the spin rotates in-plane. The IAHC obtained from first principles is found to be rather large, e.g., it amounts to 359 S/cm in Mn$_{3}$AgN. By extending our analysis to finite frequencies, we calculate the optical isotropy [$sigma_{xx}(omega)approxsigma_{yy}(omega)approxsigma_{zz}(omega)$] and the magneto-optical anisotropy [$sigma_{xy}(omega) eqsigma_{yz}(omega) eqsigma_{zx}(omega)$] of Mn$_{3}X$N. We argue that the spin-order dependent AHE and MOE are indispensable in detecting complex spin structures in noncollinear AFMs.
We report on the observation of a large topological Hall effect (THE) over a wide temperature region in a geometrically frustrated Fe3Sn2 magnet with a kagome-bilayer structure. We found that the magnitude of the THE resistivity increases with temperature and reaches -0.875 {mu}{Omega}.cm at 380 K. Moreover, the critical magnetic fields with the change of THE are consistent with the magnetic structure transformation, which indicates that the real-space fictitious magnetic field is proportional to the formation of magnetic skyrmions in Fe3Sn2. The results strongly suggest that the large THE originates from the topological magnetic spin textures and may open up further research opportunities in exploring emergent phenomena in kagome materials.
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