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1. In-plane uniaxial pressure-induced out-of-plane antiferromagnetic moment and critical fluctuations in BaFe2As2

   https://doi.org/10.1038/s41467-020-19421-5  

   Liu, Panpan; Klemm, Mason L.; Tian, Long; Lu, Xingye; Song, Yu; Tam, David W.; Schmalzl, Karin; Park, J. T.; Li, Yu; Tan, Guotai; et al (December 2020, Nature Communications)

   null (Ed.)

   Abstract A small in-plane external uniaxial pressure has been widely used as an effective method to acquire single domain iron pnictide BaFe 2 As 2 , which exhibits twin-domains without uniaxial strain below the tetragonal-to-orthorhombic structural (nematic) transition temperature T s . Although it is generally assumed that such a pressure will not affect the intrinsic electronic/magnetic properties of the system, it is known to enhance the antiferromagnetic (AF) ordering temperature T N ( <  T s ) and create in-plane resistivity anisotropy above T s . Here we use neutron polarization analysis to show that such a strain on BaFe 2 As 2 also induces a static or quasi-static out-of-plane ( c -axis) AF order and its associated critical spin fluctuations near T N / T s . Therefore, uniaxial pressure necessary to detwin single crystals of BaFe 2 As 2 actually rotates the easy axis of the collinear AF order near T N / T s , and such effects due to spin-orbit coupling must be taken into account to unveil the intrinsic electronic/magnetic properties of the system. 

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2. Dysprosium Iron Garnet Thin Films with Perpendicular Magnetic Anisotropy on Silicon

   https://doi.org/10.1002/aelm.201900820  

   Bauer, Jackson J.; Rosenberg, Ethan R.; Kundu, Subhajit; Mkhoyan, K. Andre; Quarterman, Patrick; Grutter, Alexander J.; Kirby, Brian J.; Borchers, Julie A.; Ross, Caroline A. (November 2019, Advanced Electronic Materials)

   Abstract Magnetic insulators, such as the rare‐earth iron garnets, are promising materials for energy‐efficient spintronic memory and logic devices, and their anisotropy, magnetization, and other properties can be tuned over a wide range through selection of the rare‐earth ion. Films are typically grown as epitaxial single crystals on garnet substrates, but integration of these materials with conventional electronic devices requires growth on Si. The growth, magnetic, and spin transport properties of polycrystalline films of dysprosium iron garnet (DyIG) with perpendicular magnetic anisotropy (PMA) on Si substrates and as single crystal films on garnet substrates are reported. PMA originates from magnetoelastic anisotropy and is obtained by controlling the strain state of the film through lattice mismatch or thermal expansion mismatch with the substrates. DyIG/Si exhibits large grain sizes and bulk‐like magnetization and compensation temperature. Polarized neutron reflectometry demonstrates a small interfacial nonmagnetic region near the substrate. Spin Hall magnetoresistance measurements conducted on a Pt/DyIG/Si heterostructure demonstrate a large interfacial spin mixing conductance between the Pt and DyIG comparable to other garnet/Pt heterostructures. 

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3. 19F NMR and Defect Spins in Vacuum-Annealed LaO0.5F0.5BiS2

   https://doi.org/10.1103/PhysRevB.110.235132  

   Yadav, S; Delgado, S; Bernal, O O; MacLaughlin, D E; Liu, Y; Jiang, D; Santana, O; Shu, Lei; Huang, K; Yazici, D; et al (December 2024, Physical Review B)

   We report results of magnetization and 19F NMR measurements in the normal state of as-grown vacuum-annealed LaO0.5⁢F0.5⁡BiS2. The magnetization is dominated by a temperature-independent diamagnetic component and a field- and temperature-dependent paramagnetic contribution 𝑀𝜇⁡(𝐻,𝑇) from a ∼1000 ppm concentration of local moments, an order of magnitude higher than can be accounted for by measured rare-earth impurity concentrations. 𝑀𝜇⁡(𝐻,𝑇) can be fit by the Brillouin function 𝐵𝐽⁡(𝑥) or, perhaps more realistically, a two-level tanh⁡(𝑥) model for magnetic Bi 6⁢𝑝 ions in defect crystal fields. Both fits require a phenomenological Curie-Weiss argument 𝑥=𝜇eff⁢𝐻⁡/(𝑇+𝑇𝑊), 𝑇𝑊≈1.7 K. There is no evidence for magnetic order down to 2 K, and the origin of 𝑇𝑊 is not clear. 19F frequency shifts, linewidths, and spin-lattice relaxation rates are consistent with purely dipolar 19F/defect-spin interactions. The defect-spin correlation time 𝜏𝑐⁡(𝑇) obtained from 19F spin-lattice relaxation rates obeys the Korringa relation 𝜏𝑐⁢𝑇=const, indicating the relaxation is dominated by conduction-band fluctuations. 

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4. Nematic fluctuations in an orbital selective superconductor Fe1+yTe1−xSex

   https://doi.org/10.1038/s42005-023-01154-8  

   Jiang, Qianni; Shi, Yue; Christensen, Morten H.; Sanchez, Joshua J.; Huang, Bevin; Lin, Zhong; Liu, Zhaoyu; Malinowski, Paul; Xu, Xiaodong; Fernandes, Rafael M.; et al (December 2023, Communications Physics)

   Abstract Fe 1+ y Te 1− x Se x is characterized by its complex magnetic phase diagram and highly orbital-dependent band renormalization. Despite this, the behavior of nematicity and nematic fluctuations, especially for high tellurium concentrations, remains largely unknown. Here we present a study of both B 1 g and B 2 g nematic fluctuations in Fe 1+ y Te 1− x Se x (0 ≤ x ≤ 0.53) using the technique of elastoresistivity measurement. We discovered that the nematic fluctuations in two symmetry channels are closely linked to the corresponding spin fluctuations, confirming the intertwined nature of these two degrees of freedom. We also revealed an unusual temperature dependence of the nematic susceptibility, which we attributed to a loss of coherence of the d x y orbital. Our results highlight the importance of orbital differentiation on the nematic properties of iron-based materials. 

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5. Strong variation of spin-orbit torques with relative spin relaxation rates in ferrimagnets

   https://doi.org/10.1038/s41467-023-37506-9  

   Zhu, Lijun; Ralph, Daniel C. (December 2023, Nature Communications)

   Abstract Spin-orbit torques (SOTs) have been widely understood as an interfacial transfer of spin that is independent of the bulk properties of the magnetic layer. Here, we report that SOTs acting on ferrimagnetic Fe x Tb 1- x layers decrease and vanish upon approaching the magnetic compensation point because the rate of spin transfer to the magnetization becomes much slower than the rate of spin relaxation into the crystal lattice due to spin-orbit scattering. These results indicate that the relative rates of competing spin relaxation processes within magnetic layers play a critical role in determining the strength of SOTs, which provides a unified understanding for the diverse and even seemingly puzzling SOT phenomena in ferromagnetic and compensated systems. Our work indicates that spin-orbit scattering within the magnet should be minimized for efficient SOT devices. We also find that the interfacial spin-mixing conductance of interfaces of ferrimagnetic alloys (such as Fe x Tb 1- x ) is as large as that of 3 d ferromagnets and insensitive to the degree of magnetic compensation. 

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