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1. Dilute Magnetic Impurity-Induced Effective Phonon Magnetic Moment in Fe-doped Monolayer MoS$$_2$$

   https://doi.org/10.5281/zenodo.16867938  

   JIN, WENCAN; He, Rui (January 2025, Zenodo)

   Realization of large effective phonon magnetic moment in monolayer MoS$$_2$$ has established an important route for exploring intriguing magnetic phenomena in a nonmagnetic material. The sizable coupling between the orbital transition and the circularly polarized phonon results in the large effective phonon magnetic moment. In this work, using magneto-Raman spectroscopy, we investigate substitutional doping of magnetic atoms as a tuning knob of the electronic and phononic properties of MoS$$_2$$. We show that Fe-doping polarizes the spin of the conduction bands and introduces a localized Fe band underneath the conduction band. As a result, an additional orbital transition between the Mo 4$$d$$ and Fe 3$$d$$ states emerges, producing an orbital-phonon hybridized mode at 283 cm$$^{-1}$$. Our magnetic field dependent measurements demonstrate that this new mode carries 2.8 $$\mu_B$$ effective phonon magnetic moment, which is comparable to that of the undoped MoS$$_2$$. Moreover, even though a long-range magnetic order is absent in Fe-doped MoS$$_2$$, the local magnetic moment of Fe modifies the nature of the spin fluctuation, producing monotonically increasing quasielastic scattering spectral weight as temperature decreases. Our results highlight two-dimensional dilute magnetic semiconductors synthesized by substitutional doping as a promising material platform to manipulate the phonon magnetic moment through orbital-phonon coupling. 

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2. Low-energy magnetic states of Tb adatom on graphene

   https://doi.org/10.1088/1361-648X/ad8fe9  

   Shaikh, Monirul; Klein, Alison; Wysocki, Aleksander L (November 2024, Journal of Physics: Condensed Matter)

   Abstract Electronic structure and magnetic interactions of a Tb adatom on graphene are investigated from first principles using combination of density functional theory and multiconfigurational quantum chemistry techniques including spin–orbit coupling (SOC) . We determine that the six-fold symmetry hollow site is the preferred adsorption site and investigate electronic spectrum for different adatom oxidation states including Tb³⁺, Tb²⁺, Tb¹⁺, and Tb⁰. For all charge states, the Tb $4f^8$configuration is retained with other adatom valence electrons being distributed over $5d_{xy}$, $5d_{x2+y2}$, and $6s/5d_0$single-electron orbitals. We find strong intra-site adatom exchange coupling that ensures that the $5d6s$spins are parallel to the4fspin. For Tb³⁺, the energy levels can be described by theJ = 6 multiplet split by the graphene crystal field (CF). For other oxidation states, the interaction of4felectrons with spin and orbital degrees of freedom of $6s5d$electrons in the presence of SOC results in the low-energy spectrum composed closely lying effective multiplets that are split by the graphene CF. Stable magnetic moment is predicted for Tb³⁺and Tb²⁺adatoms due to uniaxial magnetic anisotropy and effective anisotropy barrier around 440 cm⁻¹controlled by the temperature assisted quantum tunneling of magnetization through the third excited doublet. On the other hand, in-plane magnetic anisotropy is found for Tb¹⁺and Tb⁰adatoms. Our results indicate that the occupation of the $6s5d$orbitals can dramatically affect the magnetic anisotropy and magnetic moment stability of rare earth adatoms. 

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3. Magnetic order in nanogranular iron germanium (Fe _0.53 Ge _0.47 ) films

   https://doi.org/10.1088/1361-648X/ad8c0a  

   Zielinski, Ruthi; Nguyen, Nhat; Herrington, Bryce; Tarkian, Amir; Taha, Omar; Chin, Wai_Kiat; Mahmood, Ather; Chen, Xiaoqian; Klewe, Christoph; Shafer, Padraic; et al (November 2024, Journal of Physics: Condensed Matter)

   Abstract We study the effect of strain on the magnetic properties and magnetization configurations in nanogranular Fe_xGe ${}_{1-x}$films ( $x=0.53\pm 0.05$) with and without B20 FeGe nanocrystals surrounded by an amorphous structure. Relaxed films on amorphous silicon nitride membranes reveal a disordered skyrmion phase while films near and on top of a rigid substrate favor ferromagnetism and an anisotropic hybridization of Fedlevels and spin-polarized Gespband states. The weakly coupled topological states emerge at room temperature and become more abundant at cryogenic temperatures without showing indications of pinning at defects or confinement to individual grains. These results demonstrate the possibility to control magnetic exchange and topological magnetism by strain and inform magnetoelasticity-mediated voltage control of topological phases in amorphous quantum materials. 

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4. Spin stiffness and spin excitation gap of van der Waals ferromagnetic ${\mathrm{Fe}}_{3+\delta }{\mathrm{GeTe}}_2$

   https://doi.org/10.1088/1361-648X/ad581f  

   Shu, Zhixue; Zhang, Shufeng; Kong, Tai (June 2024, Journal of Physics: Condensed Matter)

   Abstract ${\mathrm{Fe}}_{3+\delta }{\mathrm{GeTe}}_2$(FGT) has proved to be an interesting van der Waals (vdW) ferromagnetic compound with a tunable Curie temperature ( $T_{\mathrm{C}}$). However, the underlying mechanism for varying $T_{\mathrm{C}}$remains elusive. Here, we systematically investigate and compare low-temperature magnetic properties of single crystalline FGT samples that exhibit $T_{\mathrm{C}}$s ranging from 160 K to 205 K. Spin stiffness (D) and spin excitation gap (Δ) are extracted using Bloch’s theory for crystals with varying Fe content. Compared to Cr-based vdW ferromagnets, FGT compounds have higher spin stiffness values but lower spin wave excitation gaps. We discuss the implication of these relationships in Fe–Fe ion magnetic interactions in FGT unit cells. The itinerancy of magnetic electrons is measured and discussed under the Rhodes–Wohlfarth ratio (RWR) and the Takahashi theory. 

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5. Connection between f-electron correlations and magnetic excitations in UTe2

   https://doi.org/10.1038/s41535-024-00720-9  

   Halloran, Thomas; Czajka, Peter; Saucedo_Salas, Gicela; Frank, Corey_E; Kang, Chang-Jong; Rodriguez-Rivera, J_A; Lass, Jakob; Mazzone, Daniel_G; Janoschek, Marc; Kotliar, Gabriel; et al (January 2025, npj Quantum Materials)

   Abstract The detailed anisotropic dispersion of the low-temperature, low-energy magnetic excitations of the candidate spin-triplet superconductor UTe₂is revealed using inelastic neutron scattering. The magnetic excitations emerge from the Brillouin zone boundary at the high symmetryYandTpoints and disperse along the crystallographic$$\hat{b}$$ $\hat{b}$-axis. In applied magnetic fields to at leastμ₀H= 11 T along the$$\hat{c}-{\rm{axis}}$$ $\hat{c}-\mathrm{axis}$, the magnetism is found to be field-independent in the (hk0) plane. The scattering intensity is consistent with that expected from U³⁺/U⁴⁺ f-electron spins with preferential orientation along the crystallographic$$\hat{a}$$ $\hat{a}$-axis, and a fluctuating magnetic moment ofμ_eff=1.7(5)μ_B. We propose interband spin excitons arising fromf-electron hybridization as a possible origin of the magnetic excitations in UTe₂. 

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