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The influence of spin-orbit coupling (SOC) on the physical properties of the 5 d 2 system Sr 2 MgOsO 6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr 2 MgOsO 6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5 d 2 system of 0.60(2) μ B  –a significantly reduced moment from the expected value for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the size of the local moment in this compound. Through comparison to Sr 2 ScOsO 6 , it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5 d 2 systems relative to their 5 d 3 counterparts, providing an explanation of the high T N found in Sr 2 MgOsO 6 .

Magnetic topological insulators are narrow-gap semiconductor materials that combine non-trivial band topology and magnetic order 1 . Unlike their nonmagnetic counterparts, magnetic topological insulators may have some of the surfaces gapped, which enables a number of exotic phenomena that have potential applications in spintronics 1 , such as the quantum anomalous Hall effect 2 and chiral Majorana fermions 3 . So far, magnetic topological insulators have only been created by means of doping nonmagnetic topological insulators with 3 d transition-metal elements; however, such an approach leads to strongly inhomogeneous magnetic 4 and electronic 5 properties of these materials, restricting the observation of important effects to very low temperatures 2 , 3 . An intrinsic magnetic topological insulator—a stoichiometric well ordered magnetic compound—could be an ideal solution to these problems, but no such material has been observed so far. Here we predict by ab initio calculations and further confirm using various experimental techniques the realization of an antiferromagnetic topological insulator in the layered van der Waals compound MnBi 2 Te 4 . The antiferromagnetic ordering  that MnBi 2 Te 4  shows makes it invariant with respect to the combination of the time-reversal and primitive-lattice translation symmetries, giving rise to a ℤ 2 topological classification; ℤ 2  = 1 for MnBi 2 Te 4 , confirming its topologically nontrivial nature. Our experiments indicate that the symmetry-breaking (0001) surface of MnBi 2 Te 4 exhibits a large bandgap in the topological surface state. We expect this property to eventually enable the observation of a number of fundamental phenomena, among them quantized magnetoelectric coupling 6 – 8 and axion electrodynamics 9 , 10 . Other exotic phenomena could become accessible at much higher temperatures than those reached so far, such as the quantum anomalous Hall effect 2 and chiral Majorana fermions 3 . An intrinsic antiferromagnetic topological insulator, MnBi 2 Te 4 , is theoretically predicted and then realized experimentally, with implications for the study of exotic quantum phenomena.

In this work, carbon nanoballs in spherical shape with diameter 70 ± 2 nm containing well-dispersed superparamagnetic magnetite/maghemite Fe 3 O 4 /γ-Fe 2 O 3 nanoparticles of 5–10 nm in size were synthesised by a facile route using the radio frequency (rf) plasma in order to assist the pyrolysis of ferrocene. Ferrocene was placed in an inductively coupled rf plasma field without additional thermal heating to activate simultaneous sublimation and pre-pyrolysis processes. During this plasma activation, the resultant derivatives were carried by an argon gas stream into the hot zone of a resistance furnace (600 °C) for complete thermal decomposition. The deposition of the nanoballs could be observed in the hot zone of the furnace at a temperature of 600 °C. The synthesised nanoballs are highly dispersible in solvents that make them particularly suitable for different applications. Their morphology, composition and structure were characterized by high-resolution scanning and transmission electron microscopy, including selected area electron diffraction, electron energy loss spectroscopy and X-ray diffraction. Magnetic measurements demonstrated that the nanoballs possess superparamagnetic characteristics.

The mineral linarite (PbCuSO\\(_4\\)(OH)\\(_2\\)) forms a monoclinic structure where a sequence of Cu(OH)\\(_2\\) units forms a spin-\\(\\frac{1}{2}\\) chain. Competing ferromagnetic nearest-neighbor (\\(J_1\\)) and antiferromagnetic next-nearest-neighbor interactions (\\(J_2\\)) in this quasi-one-dimensional spin structure imply magnetic frustration and lead to magnetic ordering below \\(T_N =\\)2.8 K in a mutliferroic elliptical spin-spiral ground state. Upon the application of a magnetic field along the spin-chain direction, distinct magnetically ordered phases can be induced. We studied the thermal conductivity \\(\\kappa\\) in this material across the magnetic phase diagram as well as in the paramagnetic regime in the temperature ranges 0.07-1 K and 9-300 K. We found that in linarite the heat is carried mainly by phonons but shows a peculiar non-monotonic behavior in field. In particular, \\(\\kappa\\) is highly suppressed at the magnetic phase boundaries, indicative of strong scattering of the phonons off critical magnetic fluctuations. Even at temperatures far above the magnetically ordered phases, the phononic thermal conductivity is reduced due to scattering off magnetic fluctuations. The mean free path due to spin-phonon scattering (\\(l_{\\text{spin-phonon}}\\)) was determined as function of temperature. A power law behavior was observed mainly above 0.5 K indicating the thermal activation of spin fluctuations. In the critical regime close to the saturation field, \\(l_{\\text{spin-phonon}}\\) shows a \\(1/T\\) dependence. Furthermore, a magnon thermal transport channel was verified in the helical magnetic phase. We estimate a magnon mean free path which corresponds to about 1000 lattice spacings.

The metallic compound FeP belongs to the class of materials that feature a complex noncollinear spin order driven by magnetic frustration. While its double-helix magnetic structure with a period \\(\\lambda_{\\text{s}} \\approx 5c\\), where \\(c\\) is the lattice constant, was previously well determined, the relevant spin-spin interactions that lead to that ground state remain unknown. By performing extensive inelastic neutron scattering measurements, we obtained the spin-excitation spectra in a large part of the momentum-energy space. The spectra show that the magnons are gapped with a gap energy of \\(\\sim\\)5 meV. Despite the 3D crystal structure, the magnon modes display strongly anisotropic dispersions, revealing a quasi-one-dimensional character of the magnetic interactions in FeP. The physics of the material, however, is not determined by the dominating exchange, which is ferromagnetic. Instead, the weaker two-dimensional antiferromagnetic interactions between the rigid ferromagnetic spin chains drive the magnetic frustration. Using linear spin-wave theory, we were able to construct an effective Heisenberg Hamiltonian with an anisotropy term capable of reproducing the observed spectra. This enabled us to quantify the exchange interactions in FeP and determine the mechanism of its magnetic frustration.

Cu Pyrimidine Cu(C4N2H4)(NO3)2(H2O)2 and Cu Benzoate Cu(C6H5COO)2·3H2O are molecule-based S 1/2 antiferromagnetic Heisenberg chain systems. Because of a staggering of the g tensor and the Dzyaloshinskii-Moriya interaction, the magnetic prinicpal axis system a′′bc′′ is distinct from the crystallographic unit cell. Along a′′ a behavior corresponding to the uniform S 1/2 antiferromagnetic Heisenberg chain occurs, while along c′′ the effect of staggering of the g tensor and Dzyaloshinskii–Moriya interaction are most prominent. Here, we discuss the field and temperature dependent magnetization along a′′ and c′′ of these systems, in particular with respect to the relevance of the inhomogeneity parameter k controlling the ratio between longitudinal and transverse magnetization components.

In this work, we report on the synthesis and magnetic properties of a series of double perovskites Ln\\(_2\\)ZnIrO\\(_6\\) with Ln = Nd, Sm, Eu & Gd. These compounds present new examples of the rare case of double perovskites (general formula A\\(_2\\)BB'O\\(_6\\)) with a magnetic 4f -ion on the A-site in combination with the strongly spin-orbit coupled 5d-transition metal ion Ir\\(^{4+}\\) on the B-sublattice. We discuss the impact of different rare earths on the macroscopic magnetic properties. Gd\\(_2\\)ZnIrO\\(_6\\) and Eu\\(_2\\)ZnIrO\\(_6\\) show weak canted antiferromagnetic order below T\\(_N\\) = 23 K and T\\(_N\\) = 12 K, respectively. Sm\\(_2\\)ZnIrO\\(_6\\) orders antiferromagnetically at T\\(_N\\) = 13 K. Nd\\(_2\\)ZnIrO\\(_6\\) exhibits complex magnetic properties with strong field dependence ranging from a two-step behavior at H = 0.01 T to an antiferromagnetic ground state at intermediate external fields and a spin-flop phase at H\\(\\geq\\)4 T, which suggests complex interplay between Nd\\(^{3+}\\) and Ir\\(^{4+}\\) . To further shed light on this magnetic interaction, the magnetic structure of Nd\\(_2\\)ZnIrO\\(_6\\)'s ground state is examined via neutron powder diffraction.

The influence of spin-orbit coupling (SOC) on the physical properties of the 5d2 system Sr2MgOsO6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering, and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr2MgOsO6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5d2 system of 0.60(2) μB a significantly reduced moment from the expected value for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap, and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the moment size in this compound. In conclusion, through comparison to Sr2ScOsO6, it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5d2 systems relative to their 5d3 counterparts, providing an explanation of the high TN found in Sr2MgOsO6.

The influence of spin-orbit coupling (SOC) on the physical properties of the 5d(2) system Sr2MgOsO6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering, and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr2MgOsO6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5d(2) system of 0.60(2) μB -a significantly reduced moment from the expected value for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap, and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the size of the local moment in this compound. Through comparison to Sr2ScOsO6, it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5d(2) systems relative to their 5d(3) counterparts, providing an explanation of the high TN found in Sr2MgOsO6.

We report an optimized chemical vapor transport method, which allows growing FeP single crystals up to 500 mg in mass and 80 \\(mm^{3}\\) in volume. The high quality of the crystals obtained by this method was confirmed by means of EDX, high-resolution TEM, low-temperature single crystal XRD and neutron diffraction experiments. We investigated the transport and magnetic properties of the single crystals and calculated the electronic band structure of FeP. We show both theoretically and experimentally, that the ground state of FeP is metallic. The examination of the magnetic data reveals antiferromagnetic order below T\\(_{N}\\) =119 K while transport remains metallic in both the paramagnetic and the antiferromagnetic phase. The analysis of the neutron diffraction data shows an incommensurate magnetic structure with the propagation vector Q=(0, 0, \\(\\pm{\\delta}\\)), where \\({\\delta}\\) \\(\\sim\\) 0.2. For the full understanding of the magnetic state, further experiments are needed. The successful growth of large high-quality single crystals opens the opportunity for further investigations of itinerant magnets with incommensurate spin structures using a wide range of experimental tools.