Excitons in Correlated van der Waals Antiferromagnetic Nanostructures
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Robust Biaxial Anisotropy and Switchable Néel Vectors in LaFeO 3 Epitaxial Films
Antiferromagnets with highly stable but switchable Néel vectors are desired for antiferromagnetic spintronics with ultrafast speed and terahertz frequencies. Electrical switching of antiferromagnetic insulators has been demonstrated using binary antiferromagnets, while large families of complex antiferromagnets such as perovskites are largely unexplored. Here, we show that epitaxial LaFeO 3 thin films on SrTiO 3 (001) exhibit clear, robust biaxial anisotropy with a spin-flop field of a few tesla. Angular-dependent spin-Hall magnetoresistance (SMR) characterizations of Pt/LaFeO 3 bilayers with the current channel along SrTiO 3 [100] and [110] reveal distinct, intriguing shapes and field dependence. Simulations using a macrospin model accurately describe the main behavior and fine features of the SMR data from which key antiferromagnetic parameters are extracted. Furthermore, remanent SMR measurement confirms the high fidelity of the Néel vector along either easy axis of the biaxial anisotropy, indicating that epitaxial films of LaFeO 3 and potentially other perovskite antiferromagnets offer an attractive platform for antiferromagnetic spintronics.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Mo{sub 2}NiB{sub 2}-type (Gd, Tb, Dy){sub 2}Ni{sub 2.35}Si{sub 0.65} and La{sub 2}Ni{sub 3}-type (Dy, Ho){sub 2}Ni{sub 2.5}Si{sub 0.5} compounds: Crystal structure and magnetic properties
The crystal structure of new Mo{sub 2}NiB{sub 2}-type (Gd, Tb, Dy){sub 2}Ni{sub 2.35}Si{sub 0.65} (Immm, No. 71, oI10) and La{sub 2}Ni{sub 3}-type (Dy, Ho){sub 2}Ni{sub 2.5}Si{sub 0.5} (Cmce No. 64, oC20) compounds has been established using powder X-ray diffraction studies. Magnetization measurements show that the Mo{sub 2}NiB{sub 2}-type Gd{sub 2}Ni{sub 2.35}Si{sub 0.65} undergoes a ferromagnetic transition at ~66 K, whereas isostructural Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} shows an antiferromagnetic transition at ~52 K and a field-induced metamagnetic transition at low temperatures. Neutron diffraction study shows that, in zero applied field, Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} exhibits c-axis antiferromagnetic order with propagation vector K=[1/2, 0, 1/2] below its magnetic ordering temperature and Tb magnetic moment reaches a value of 8.32(5) μ{sub B} at 2 K. The La{sub 2}Ni{sub 3}-type Dy{sub 2}Ni{sub 2.5}Si{sub 0.5} exhibits ferromagnetic like transition at ~42 K with coexisting antiferromagnetic interactions and field induced metamagnetic transition below ~17 K. The magnetocaloric effect of Gd{sub 2}Ni{sub 2.35}Si{sub 0.65}, Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} and Dy{sub 2}Ni{sub 2.5}Si{sub 0.5} is calculated in terms of isothermal magnetic entropy change and it reaches a maximum value of −14.3 J/kg K, −5.3 J/kg K and −10.3 J/kg K for a field change of 50 kOe near 66 K, 52 K and 42 K, respectively. Low temperature magnetic ordering with enhanced anisotropic effects in Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} and Dy{sub 2}Ni{sub 2.35}Si{sub 0.65} is accompanied by a positive magnetocaloric effect with isothermal magnetic entropy changes of +12.8 J/kg K and ~+9.9 J/kg K, respectively at 7 K for a field change of 50 kOe. - Graphical abstract: The (Gd, Tb, Dy){sub 2}Ni{sub 2.35}Si{sub 0.65} supplement the series of Mo{sub 2}NiB{sub 2}-type rare earth compounds, whereas the (Dy, Ho){sub 2}Ni{sub 2.5}Si{sub 0.5} supplement the series of La{sub 2}Ni{sub 3}-type rare earth compounds. The variation of alloy’s composition by ~3 at% i.e. from Dy{sub 2}Ni{sub 2.35}Si{sub 0.65} to Dy{sub 2}Ni{sub 2.5}Si{sub 0.5} leads to significant transformation of crystal structure of compound with different variant of distortion of Po-type rare earth sublattice, as in Gd–Co–Ga and Er–Ni–In systems: the Mo{sub 2}NiB{sub 2}-type Gd{sub 2}Co{sub 2}Ga and La{sub 2}Ni{sub 3}-type Gd{sub 2}Co{sub 2.9}Ga{sub 0.1}, and Mo{sub 2}FeB{sub 2}-type Er{sub 2}Ni{sub 1.78}In and Mn{sub 2}AlB{sub 2}-type Er{sub 2}Ni{sub 2}In. Magnetization measurements indicate collinear ferromagnetic ordering of Mo{sub 2}NiB{sub 2}-type Gd{sub 2}Ni{sub 2.35}Si{sub 0.65} and a complex antiferromagnetic ordering with low-temperature metamagnetic nature for Mo{sub 2}NiB{sub 2}-type Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} compounds. However, neutron diffraction study in zero applied field of Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} reveals c-axis pure antiferromagnetic ordering of terbium sublattice with K=[1/2, 0, 1/2] propagation vector. Magnetization measurements indicate ferromagnetic order with coexisting antiferromagnetic interactions and low-temperature metamagnetic state for La{sub 2}Ni{sub 3}-type Dy{sub 2}Ni{sub 2.5}Si{sub 0.5}. We suggest possible polymorphism in other Mo{sub 2}FeB{sub 2}-type, Mo{sub 2}NiB{sub 2}-type, La{sub 2}Ni{sub 3}-type and Mn{sub 2}AlB{sub 2}-type rare earth compounds with corresponding change in their magnetic properties. - Highlights: • (Gd, Tb, Dy){sub 2}Ni{sub 2.35}Si{sub 0.65} compounds crystallize in the Mo{sub 2}NiB{sub 2}-type structure. • (Dy, Ho){sub 2}Ni{sub 2.5}Si{sub 0.5} compounds crystallize in the La{sub 2}Ni{sub 3}-type structure. • Gd{sub 2}Ni{sub 2.35}Si{sub 0.65} shows pure ferromagnetic type ordering. • Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} and Dy{sub 2}Ni{sub 2.5}Si{sub 0.5} show mixed ferro-antiferromagnetic ordering. • Tb{sub 2}Ni{sub 2.35}Si{sub 0.65} and Dy{sub 2}Ni{sub 2.5}Si{sub 0.5} exhibit low-temperature metamagnetic behaviour.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Synthesis, crystal growth, structural and magnetic characterization of NH{sub 4}MCl{sub 2}(HCOO), M=(Fe, Co, Ni)
An ambient-pressure solution route and an improved solvothermal synthetic method have been developed to produce polycrystalline powders and large single crystals of NH{sub 4}MCl{sub 2}(HCOO) (M=Fe, Co, Ni). The magnetic structure of the 1D linear chain compound NH{sub 4}FeCl{sub 2}(HCOO) has been determined by low-temperature neutron powder diffraction, revealing ferromagnetic intra-chain interactions and antiferromagnetic inter-chain interactions. The newly-reported Co and Ni analogs are isostructural with NH{sub 4}FeCl{sub 2}(HCOO), but there are significant differences in the magnetic properties of each compound; the Ni analog behaves similarly to the Fe compound but with stronger magnetic coupling, exhibiting antiferromagnetic ordering (T{sub N}=8.5 K) and a broad metamagnetic transition between 2 and 5 T, while the Co analog does not order magnetically above 2 K, despite strong antiferromagnetic nearest-neighbor interactions. - Graphical abstract: Large single crystals of NH{sub 4}MCl{sub 2}(HCOO) (M=Fe, Co, Ni), which adopt a 1D zig-zag chain structure, can be grown via a solvothermal method. Neutron diffraction experiments revealed that the magnetic structure of the iron compound exhibits ferromagnetic intra-chain coupling and antiferromagnetic inter-chain coupling. - Highlights: • Large crystals of NH{sub 4}MCl{sub 2}(HCOO) (M=Fe, Co, Ni) have been grown solvothermally. • The magnetic structure of M=Fe was solved by low-temperature neutron diffraction. • NH{sub 4}FeCl{sub 2}(HCOO) exhibits FM intra-chain and AFM inter-chain interactions. • NH{sub 4}CoCl{sub 2}(HCOO) exhibits no 3D magnetic ordering above 2 K. • NH{sub 4}NiCl{sub 2}(HCOO) exhibits AFM ordering (T{sub N}=8.5 K) and FM intra-chain interactions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ionic Liquid Gating Control of RKKY Interaction in FeCoB/Ru/FeCoB and (Pt/Co) 2 /Ru/(Co/Pt) 2 Multilayers.
To overcome the fundamental challenge of the weak natural response of antiferromagnetic materials under a magnetic field, voltage manipulation of antiferromagnetic interaction is developed to realize ultrafast, high-density, and power efficient antiferromagnetic spintronics. Here, we report a low voltage modulation of Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction via ionic liquid gating in synthetic antiferromagnetic multilayers of FeCoB/Ru/FeCoB and (Pt/Co) 2 /Ru/(Co/Pt) 2 . At room temperature, the distinct voltage control of transition between antiferromagnetic and ferromagnetic ordering is realized and up to 80% of perpendicular magnetic moments manage to switch with a small-applied voltage bias of 2.5 V. We related this ionic liquid gating-induced RKKY interaction modification to the disturbance of itinerant electrons inside synthetic antiferromagnetic heterostructure and the corresponding change of its Fermi level. In conclusion, voltage tuning of RKKY interaction may enable the next generation of switchable spintronics between antiferromagnetic and ferromagnetic modes with both fundamental and practical perspectives.
36 MATERIALS SCIENCE↗
Neutron diffraction study of monoclinic brannerite-type CoV{sub 2}O{sub 6}
A variable-temperature powder neutron diffraction study of the monoclinic brannerite-type CoV{sub 2}O{sub 6} (space group C2/m, a=9.2531(2), b=3.5040(1), c=6.6201(1) A and {beta}=111.617(1) Degree-Sign at 300 K) is reported. No structural transition is observed down to 4 K, but a magnetostriction accompanying antiferromagnetic order at T{sub N}=15 K is discovered. Antiferromagnetic order observed below T{sub N} has an a Multiplication-Sign b Multiplication-Sign 2c supercell in which Co{sup 2+} moments of magnitude 4.77(4) {mu}{sub B} at 4 K lie in the ac plane and are ferromagnetically coupled within chains of edge-sharing CoO{sub 6} octahedra parallel to b. Ferromagnetic chains are coupled antiferromagnetically to neighbouring chains in the a and c directions, and a model for the interchain order in the reported 1/3 magnetization plateau region is proposed. - Graphical abstract: Antiferromagnetic order of Co{sup 2+} moments in monoclinic brannerite type CoV2O6 results in a magnetostriction at the 15 K Neel transition. An alternative coupling between ferromagnetic chains is proposed to account for a 1/3 magnetization plateau in this material. Highlights: Black-Right-Pointing-Pointer Variable-temperature powder neutron diffraction study of the monoclinic brannerite-type CoV{sub 2}O{sub 6} is reported. Black-Right-Pointing-Pointer Magnetostriction accompanying antiferromagnetic order at T{sub N}=15 K in monoclinic CoV{sub 2}O{sub 6} is discovered. Black-Right-Pointing-Pointer Antiferromagnetic order in a Multiplication-Sign b Multiplication-Sign 2c supercell of CoV{sub 2}O{sub 6} is determined. Black-Right-Pointing-Pointer Model for spin order in the reported 1/3 magnetization plateau of CoV{sub 2}O{sub 6} is proposed.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Crystal structures and magnetic properties of lanthanide containing borates LnM(BO{sub 3}){sub 2} (Ln=Y, Ho–Lu; M=Sc, Cr)
The synthesis, crystal structures and magnetic properties of LnM(BO{sub 3}){sub 2} (Ln=Y, Ho–Lu; M=Sc, Cr) were investigated. The LnCr(BO{sub 3}){sub 2} compounds crystallize in the dolomite-type structure with space group R3{sup ¯}, in which the Ln and Cr ions occupy two octahedral sites. From the result of structural analysis, it was found that there is an anti-site disorder between these two sites and its chemical formula is more exactly Ln{sub 1−r}Cr{sub r}[Cr{sub 1−r}Ln{sub r}](BO{sub 3}){sub 2}. On the other hand, the LnSc(BO{sub 3}){sub 2} adopt the calcite-type structure with space group R3{sup ¯}c. The Ln and Sc ions randomly occupy an octahedral site and the chemical formula is represented as (Ln{sub 0.5}Sc{sub 0.5})BO{sub 3}. From the magnetic susceptibility and specific heat measurements, we found that all the LnCr(BO{sub 3}){sub 2} show an antiferromagnetic transition at 6.1–8.1 K. This transition is mainly due to the ordering of Cr{sup 3+} magnetic moments. Among the compounds with magnetic Ln{sup 3+} ions, only YbCr(BO{sub 3}){sub 2} shows an antiferromagnetic ordering of Ln{sup 3+} ion at 2.1 K. - Graphical abstract: The lanthanide containing borates LnM(BO{sub 3}){sub 2} (Ln=Y, Ho–Lu; M=Sc, Cr) have the dolomite-type (Ln=Cr) and calcite-type (Ln=Sc) structures. Both structures are similar to each other except for the difference in the partially or fully disordered arrangements of octahedral sites. At low temperatures, the LnCr(BO{sub 3}){sub 2} compounds show an antiferromagnetic transition due to a long-range ordering of Cr{sup 3+} moments. Among them only YbCr(BO{sub 3}){sub 2} shows an antiferromagnetic ordering of Ln{sup 3+} ion at 2.1 K. Display Omitted - Highlights: • Lanthanide containing borates LnM(BO{sub 3}){sub 2} (Ln=Y, Ho–Lu; M=Sc, Cr) have been synthesized. • LnCr(BO{sub 3}){sub 2} has the dolomite-type structure with an anti-site disorder between Ln and Cr sites. • LnSc(BO{sub 3}){sub 2} has the calcite-type structure in which the Ln and Cr randomly occupy the same site. • LnCr(BO{sub 3}){sub 2} shows an antiferromagnetic transition at 6.1–8.1 K due to the long-range magnetic ordering of Cr{sup 3+} moments. • Only YbCr(BO{sub 3}){sub 2} shows the two-step antiferromagnetic ordering: Cr{sup 3+} (6.1 K) and Yb{sup 3+} (2.1 K)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Electronic, structural and magnetic studies of niobium borides of group 8 transition metals, Nb{sub 2}MB{sub 2} (M=Fe, Ru, Os) from first principles calculations
The Nb{sub 2}FeB{sub 2} phase (U{sub 3}Si{sub 2}-type, space group P4/mbm, no. 127) is known for almost 50 years, but until now its magnetic properties have not been investigated. While the synthesis of Nb{sub 2}OsB{sub 2} (space group P4/mnc, no. 128, a twofold superstructure of U{sub 3}Si{sub 2}-type) with distorted Nb-layers and Os{sub 2}-dumbbells was recently achieved, “Nb{sub 2}RuB{sub 2}” is still not synthesized and its crystal structure is yet to be revealed. Our first principles density functional theory (DFT) calculations have confirmed not only the experimental structures of Nb{sub 2}FeB{sub 2} and Nb{sub 2}OsB{sub 2}, but also predict “Nb{sub 2}RuB{sub 2}” to crystalize with the Nb{sub 2}OsB{sub 2} structure type. According to chemical bonding analysis, the homoatomic B–B interactions are optimized and very strong, but relatively strong heteroatomic M–B, B–Nb and M–Nb bonds (M=Fe, Ru, Os) are also found. These interactions, which together build a three-dimensional network, are mainly responsible for the structural stability of these ternary borides. The density-of-states at the Fermi level predicts metallic behavior, as expected, from metal-rich borides. Analysis of possible magnetic structures concluded preferred antiferromagnetic ordering for Nb{sub 2}FeB{sub 2}, originating from ferromagnetic interactions within iron chains and antiferromagnetic exchange interactions between them. -- Graphical abstract: Nb{sub 2}FeB{sub 2} (U{sub 3}Si{sub 2} structure type, space group P4/mbm, no. 127) is predicted to order antiferromagnetically, due to the presence of iron chains which show ferromagnetic interactions in the chains and antiferromagnetic interactions between them. “Nb{sub 2}RuB{sub 2}” is predicted to crystallize with the recently discovered Nb{sub 2}OsB{sub 2} twofold superstructure (space group P4/mnc, no. 128) of U{sub 3}Si{sub 2} structure type. The building of ruthenium dumbbells instead of chains along [001] is found to be responsible for the stabilization of this superstructure. Highlights: • Nb{sub 2}FeB{sub 2} is predicted to order antiferromagnetically. • Ferromagnetic interactions found in iron chains and antiferromagnetic ones between them. • Unknown “Nb{sub 2}RuB{sub 2}” predicted to crystallize with a twofold U{sub 3}Si{sub 2} superstructure. • Puckering of Nb-layer and Ru-dumbbell formation responsible for superstructure occurrence.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Single crystal and magnetic structures of maricite-type AgMnVO{sub 4}
Single crystals of the ternary manganese vanadate AgMnVO{sub 4}, were grown using AgVO{sub 3} flux. The structure was determined from single crystal X-ray diffraction data. The magnetic structure and properties of AgMnVO{sub 4} were characterized by magnetic susceptibility, specific heat, and low-temperature neutron powder diffraction measurements. AgMnVO{sub 4} crystallizes in the maricite-type structure with space group Pnma, a=9.5393(12), b=6.8132(9), c=5.3315(7) Å and Z=4. AgMnVO{sub 4} contains MnO{sub 4} chains made up of edge-sharing MnO{sub 6} octahedra, and these chains are interlinked by the VO{sub 4} and AgO{sub 4} tetrahedra. The specific heat measurements indicate a 3D-antiferromagnetic ordering at ∼12.1 K and the neutron powder diffraction measurements at 5 K show that the Mn{sup 2+}magnetic moments are antiferromagnetically coupled within the chains which are antiferromagnetically coupled to each other. - Graphical abstract: The AgMnVO{sub 4} crystals could be grown in AgVO{sub 3} flux and the magnetic structure was determined from neutron powder diffraction data. The spins in each MnO{sub 4} chain along [0 1 0] are antiferromagnetically coupled, while these antiferromagnetic chains are antiferromagnetically coupled along [0 0 1] but have a non-collinear arrangement along [1 0 1]. - Highlights: • We have been able to grow AgMnVO{sub 4} single crystals, using AgVO{sub 3} flux. • We solved its crystal structure using single crystal data. • We carried out magnetic susceptibility and specific heat measurements. • We solved the magnetic structure from low-temperature neutron powder diffraction data. • We compared the magnetic structure to that of NaFePO{sub 4}.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Observation of Quantum Anomalous Hall Effect and Exchange Interaction in Topological Insulator/Antiferromagnet Heterostructure
Integration of a quantum anomalous Hall insulator with a magnetically ordered material provides an additional degree of freedom through which the resulting exotic quantum states can be controlled. Here, an experimental observation is reported of the quantum anomalous Hall e?ect in a magnet-ically-doped topological insulator grown on the antiferromagnetic insulator Cr?O?. The exchange coupling between the two materials is investigated using ?eld-cooling-dependent magnetometry and polarized neutron re?ec-tometry. Both techniques reveal strong interfacial interaction between the antiferromagnetic order of the Cr?O? and the magnetic topological insulator, manifested as an exchange bias when the sample is ?eld-cooled under an out-of-plane magnetic ?eld, and an exchange spring-like magnetic depth pro?le when the system is magnetized within the ?lm plane. These results identify antiferromagnetic insulators as suitable candidates for the manipula-tion of magnetic and topological order in topological insulator ?lms.
Pan, Lei↗
Bogoliubov quasiparticle on the gossamer Fermi surface in electron-doped cuprates
Electron-doped cuprates consistently exhibit strong antiferromagnetic correlations, leading to the prevalent belief that antiferromagnetic spin fluctuations mediate Cooper pairing in these unconventional superconductors. However, early investigations showed that although antiferromagnetic spin fluctuations create the largest pseudogap at hot spots in momentum space, the superconducting gap is also maximized at these locations. This presented a paradox for spin-fluctuation-mediated pairing: Cooper pairing is strongest at momenta where the normal-state low-energy spectral weight is most suppressed. Here we investigate this paradox and find evidence that a gossamer—meaning very faint—Fermi surface can provide an explanation for these observations. We study Nd 2–x Ce x CuO 4 using angle-resolved photoemission spectroscopy and directly observe the Bogoliubov quasiparticles. First, we resolve the previously observed reconstructed main band and the states gapped by the antiferromagnetic pseudogap around the hot spots. Within the antiferromagnetic pseudogap, we also observe gossamer states with distinct dispersion, from which coherence peaks of Bogoliubov quasiparticles emerge below the superconducting critical temperature. Moreover, the direct observation of a Bogoliubov quasiparticle permits an accurate determination of the superconducting gap, yielding a maximum value an order of magnitude smaller than the pseudogap, establishing the distinct nature of these two gaps. Here we propose that orientation fluctuations in the antiferromagnetic order parameter are responsible for the gossamer states.
36 MATERIALS SCIENCE↗
Quantum spin nematic phase in a square-lattice iridate
Spin nematic is a magnetic analogue of classical liquid crystals, a fourth state of matter exhibiting characteristics of both liquid and solid. Particularly intriguing is a valence-bond spin nematic, in which spins are quantum entangled to form a multipolar order without breaking time-reversal symmetry, but its unambiguous experimental realization remains elusive. Here, in this study, we establish a spin nematic phase in the square-lattice iridate Sr 2 IrO 4 , which approximately realizes a pseudospin one-half Heisenberg antiferromagnet in the strong spin-orbit coupling limit. Upon cooling, the transition into the spin nematic phase at T C approximate to 263 K is marked by a divergence in the static spin quadrupole susceptibility extracted from our Raman spectra and concomitant emergence of a collective mode associated with the spontaneous breaking of rotational symmetries. The quadrupolar order persists in the antiferromagnetic phase below TN approximate to 230 K and becomes directly observable through its interference with the antiferromagnetic order in resonant X-ray diffraction, which allows us to uniquely determine its spatial structure. Further, we find using resonant inelastic X-ray scattering a complete breakdown of coherent magnon excitations at short-wavelength scales, suggesting a many-body quantum entanglement in the antiferromagnetic state. Taken together, our results reveal a quantum order underlying the Neel antiferromagnet that is widely believed to be intimately connected to the mechanism of high-temperature superconductivity. We establish a spin nematic phase in the square-lattice iridate Sr 2 IrO 4 and find a complete breakdown of coherent magnon excitations at short-wavelength scales, suggesting a many-body quantum entanglement in the antiferromagnetic state.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Mn(Pt 1–x Pd x ) 5 P: Isovalent tuning of Mn-sublattice magnetic order
Here, e report the growth and characterization of MnPd 5 P, a rare-earth-free ferromagnet, with T C ≈ 295 K and planar anisotropy, and conduct a substitutional study with its antiferromagnetic analogue MnPt 5 P. We provide a solution route to grow large single crystals of MnPd 5 P and the series Mn(Pt 1–x Pd x ) 5 P by adding Mn into Pd-P and (Pt 1–x Pd x )-P based melts. All compounds in the family adopt the layered anti-CeCoIn5 type structure with the space group P4/mmm, and EDS and X-ray diffraction results indicate that MnPt 5 P and MnPd 5 P form a complete solid solution. Based on measurements of the temperature- and field-dependent magnetization and resistance, we construct a temperature-composition (T-x) phase diagram for Mn(Pt 1–x Pd x ) 5 P and demonstrate that the initial antiferromagnetic order found in MnPt 5 P is extraordinarily sensitive to Pd substitution. At low Pd fractions (x < 0.010), the single antiferromagnetic transition in pure MnPt 5 P splits into a higher temperature ferromagnetic transition followed first, upon cooling, by a lower temperature ferromagnetic to antiferromagnetic transition and then by a re-entrant antiferromagnetic to ferromagnetic transition at even lower temperatures. The antiferromagnetic region makes up a bubble phase that persists up to x ≈ 0.008-0.009 for T ≈ 150 K, with all samples x < 0.008 recovering their initial ferromagnetic state upon further cooling to base temperature. Over the same low substitution range we find a non-monotonic change in the room temperature value of the unit cell volume, further suggesting that pure MnPt 5 P is very close to an instability. Once x > 0.010, Mn(Pt 1–x Pd x ) 5 P undergoes a only single transition into the ferromagnetic phase. The Curie temperature initially increases rapidly with x, rising from T C ≈ 197 K at x = 0.013 to a maximum of T C ≈ 312 K for x ≈ 0.62, and then falling back to T C ≈ 295 K for pure MnPd 5 P (x = 1.00). Given that Pt and Pd are isoelectronic, this work raises questions as to the origin of the extreme sensitivity of the magnetic ground state in MnPt 5 P upon introducing Pd.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Magnetic measurements and neutron diffraction study of the layered hybrid compounds Mn(C{sub 8}H{sub 4}O{sub 4})(H{sub 2}O){sub 2} and Mn{sub 2}(OH){sub 2}(C{sub 8}H{sub 4}O{sub 4})
Mn(C{sub 8}H{sub 4}O{sub 4})(H{sub 2}O){sub 2} and Mn{sub 2}(OH){sub 2}(C{sub 8}H{sub 4}O{sub 4}) layered organic-inorganic compounds based on manganese(II) and terephthalate molecules (C{sub 8}H{sub 4}O{sub 4}{sup 2-}) have been studied by DC and AC magnetic measurements and powder neutron diffraction. The dihydrated compound behaves as a 3D antiferromagnet below 6.5 K. The temperature dependence of its {chi}T product is typical of a 2D Heisenberg system and allows determining the in-plane exchange constant J Almost-Equal-To -7.4 K through the carboxylate bridges. The magnetic structure confirms the in-plane nearest neighbor antiferromagnetic interactions and the 3D ordering. The hydroxide based compound also orders as a 3D antiferromagnet with a higher Neel temperature (38.5 K). Its magnetic structure is described from two antiferromagnetically coupled ferromagnetic sublattices, in relation with the two independent metallic sites. The isothermal magnetization data at 2 K are consistent with the antiferromagnetic ground-state of these compounds. However, in both cases, a slope change points to field-induced modification of the magnetic structure. - Graphical abstract: The macroscopic magnetic properties and magnetic structures of two metal-organic frameworks based on manganese (II) and terephthalate molecules are presented. Highlights: Black-Right-Pointing-Pointer Magnetic study of Mn(C{sub 8}H{sub 4}O{sub 4})(H{sub 2}O){sub 2} and Mn{sub 2}(OH){sub 2}(C{sub 8}H{sub 4}O{sub 4}). Black-Right-Pointing-Pointer Two compounds with common features (interlayer linker/distance, S=5/2 spin). Black-Right-Pointing-Pointer Magnetic measurements quantitatively analyzed to deduce exchange constants. Black-Right-Pointing-Pointer Magnetic structures determined from neutron powder diffraction experiments.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Crystal structure and magnetic properties of novel Hf{sub 3}Ni{sub 2}Si{sub 3}-type R{sub 3}Co{sub 2}Ge{sub 3} compounds (R=Y, Sm, Tb-Tm)
The novel R{sub 3}Co{sub 2}Ge{sub 3} compounds with R=Y, Sm, Tb-Tm adopt the Hf{sub 3}Ni{sub 2}Si{sub 3}-type structure (ordered variant of the Ca{sub 3}Ga{sub 5}-type one, space group Cmcm). Sm{sub 3}Co{sub 2}Ge{sub 3}, Tb{sub 3}Co{sub 2}Ge{sub 3}, Ho{sub 3}Co{sub 2}Ge{sub 3} and Er{sub 3}Co{sub 2}Ge{sub 3} undergo an antiferromagnetic-type ordering and Tb{sub 3}Co{sub 2}Ge{sub 3} demonstrates a field-sensitive magnetic behavior. Tm{sub 3}Co{sub 2}Ge{sub 3} is a pure paramagnet down to 5 K, whereas Y{sub 3}Co{sub 2}Ge{sub 3} demonstrates Pauli paramagnetism down to {approx}120 K. In zero applied field and between {approx}50 and {approx}15 K Tb{sub 3}Co{sub 2}Ge{sub 3} shows a non-collinear antiferromagnetic ordering with wave vectors K{sub 0}=[0, 0, 0] and K{sub 1}=[{+-}1/3, 0, 0] and a magnetic unit cell 3a{sub Tb{sub 3Co{sub 2Ge{sub 2}}}} Multiplication-Sign b{sub Tb{sub 3Co{sub 2Ge{sub 3}}}} Multiplication-Sign c{sub Tb{sub 3Co{sub 2Ge{sub 3}}}} , whereas below {approx}15 K it exhibits a complex antiferromagnetic ordering with K{sub 0}=[0, 0, 0], K{sub 1}=[{+-}1/3, 0, 0] and K{sub 2}=[1/2, 0, 0] wave vectors and magnetic unit cell 6a{sub Tb{sub 3Co{sub 2Ge{sub 2}}}} Multiplication-Sign b{sub Tb{sub 3Co{sub 2Ge{sub 2}}}} Multiplication-Sign c{sub Tb{sub 3Co{sub 2Ge{sub 2}}}}. - Graphical abstract: The Hf{sub 3}Ni{sub 2}Si{sub 3}-type {l_brace}Y, Sm, Gd-Tm{r_brace}{sub 3}Co{sub 2}Ge{sub 3} (space group Cmcm) demonstrate complex field sensitive antiferromagnetic ordering. The rare earth sublattice of 4d site plays crucial role in the magnetisation of R{sub 3}Co{sub 2}Ge{sub 3} compounds. Highlights: Black-Right-Pointing-Pointer The {l_brace}Y, Sm, Gd-Tm{r_brace}{sub 3}Co{sub 2}Ge{sub 3} adopts the Hf{sub 3}Ni{sub 2}Si{sub 3}-type structure (space group Cmcm). Black-Right-Pointing-Pointer They demonstrate complex field sensitive antiferromagnetic ordering. Black-Right-Pointing-Pointer The 4d site rare earth sublattice plays crucial role in the magnetism of R{sub 3}Co{sub 2}Ge{sub 3}.
36 MATERIALS SCIENCE↗
Three new homochiral coordination polymers involving two three-dimensional structural architectures: Syntheses, structures and magnetic properties
The preparations and properties of three new homochiral three-dimensional (3D) coordination polymers, [M(D-cam)(pyz)(H{sub 2}O){sub 2}]{sub n} (M=Co (1) and Ni (2); D-H{sub 2}cam=(+) D-camphoric acid; pyz=pyrazine) and [Mn{sub 2}(D-cam){sub 2}(H{sub 2}O){sub 2}] (3), under solvothermal conditions is described. Single-crystal X-ray diffraction analyses revealed that all of compounds are homochiral 3D structure. 1 and 2 are isostructural and crystallize in the trigonal space group P3{sub 2}21, while 3 crystallizes in monoclinic space group P2{sub 1}. The structure of 1 and 2 consists of metal-D-cam helical chains which are pillared with pyrazine ligands into a 3D framework structure and 3 features a 3D homochiral framework involving one-dimensional manganese-carboxylate chains that are aligned parallel to the b axis. Magnetic susceptibility data of all compounds were collected. The findings indicate that μ{sub 2}-pyrazine dominate weak antiferromagnetic coupling within 1 and 2, while 3 exhibits antiferromagnetic behavior through the carboxylate groups of D-cam ligand. -- Graphical abstract: The preparations and properties of three new homochiral three-dimensional (3D) coordination polymers, [M(D-cam)(pyz)(H{sub 2}O){sub 2}]{sub n} (M=Co (1) and Ni (2); D-H{sub 2}cam=(+) D-camphoric acid; pyz=pyrazine) and [Mn{sub 2}(D-cam){sub 2}(H{sub 2}O){sub 2}] (3), under solvothermal conditions is described. Single-crystal X-ray diffraction analyses revealed that all of compounds are homochiral 3D structure. 1 and 2 are isostructural and crystallize in the trigonal space group P3{sub 2}21, while 3 crystallizes in monoclinic space group P2{sub 1}. The structure of 1 and 2 consists of metal-D-cam helical chains which are pillared with pyrazine ligands into a 3D framework structure and 3 features a 3D homochiral framework involving one-dimensional manganese-carboxylate chains that are aligned parallel to the b axis. Magnetic susceptibility data of all compounds were collected. The findings indicate that μ{sub 2}-pyrazine dominate weak antiferromagnetic coupling within 1 and 2, while 3 exhibits antiferromagnetic behavior through the carboxylate groups of D-cam ligand. Highlights: • Three homochiral 3D coordination polymers were synthesized. • 1 and 2 are 3D structure with metal-D-cam helical chains pillared by pyrazine. • 3 shows a 3D homochiral framework involving 1D manganese-carboxylate chains. • Magnetic data analysis indicates that 1–3 exhibit weak antiferromagnetic coupling.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Synthesis, structure, and magnetic properties of the novel sodium cobalt tellurate Na{sub 5}Co{sub 15.5}Te{sub 6}O{sub 36}
The novel single crystal oxide Na{sub 5}Co{sub 15.5}Te{sub 6}O{sub 36} had been successfully synthesized by a self-flux method. Na{sub 5}Co{sub 15.5}Te{sub 6}O{sub 36} crystallizes in hexagonal symmetry, space group P6{sub 3}/m (No.176), with lattice parameters a=9.359 (3) Å, c=9.096 (8) Å, and Z=1. The structure is composed of combining the edge-sharing chains of octahedra, [TeO{sub 6}]{sup 6−} and [Co(1)O{sub 6}]{sup 10−} with the face-sharing chains of triangular prisms, [Co(2)O{sub 6}]{sup 10−} and [Co(3)(Na(3))O{sub 6}]{sup 10−}. Sodium ions partially occupy hexagonal channels along the c-axis that are formed by the connection of the chains. The magnetic susceptibility data show a long-range antiferromagnetic ordering with a Neel temperature of 52 K along the c axis. At temperatures above 200 K, the susceptibility corrected for the diamagnetic contribution can be fit to the Curie–Weiss law for Co{sup 2+} (S=3/2). The anisotropic ferromagnetic and antiferromagnetic feature of Na{sub 5}Co{sub 15.5}Te{sub 6}O{sub 36} was obtained through field-dependent magnetization measurements at low temperature. The ferromagnetic and antiferromagnetic behaviors can be considered from the interactions between the Co ions in 1D zig-zag chains formed by sharing the edges of the Co(1)O{sub 6} octahedra, and the interactions between the interchain Co ions, respectively. -- Graphical abstract: The unit cell (a) and perspective view along [001] (b) of novel single crystal oxide, Na{sub 5}Co{sub 15.5}Te{sub 6}O{sub 36}. Highlights: • A single crystal of Na{sub 5}Co{sub 15.5}Te{sub 6}O{sub 36} has been synthesized by a self-flux method. • Na{sub 5}Co{sub 15.5}Te{sub 6}O{sub 36} crystallizes in hexagonal symmetry with a space group P6{sub 3}/m. • Na{sub 5}Co{sub 15.5}Te{sub 6}O{sub 36} has an antiferromagnetic ordering with a Neel temperature of 52 K. • Na{sub 5}Co{sub 15.5}Te{sub 6}O{sub 36} shows anisotropic ferro- and antiferromagnetism at low temperatures.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Oxygen trapped by rare earth tetrahedral clusters in Nd{sub 4}FeOS{sub 6}: Crystal structure, electronic structure, and magnetic properties
Single crystals of Nd{sub 4}FeOS{sub 6} were grown from an Fe–S eutectic solution. Single crystal X-ray diffraction analysis revealed a Nd{sub 4}MnOSe{sub 6}-type structure (P6{sub 3}mc, a=9.2693(1) Å, c=6.6650(1)Å, V=495.94(1) Å{sup 3}, Z=2), featuring parallel chains of face-sharing [FeS{sub 6×1/2}]{sup 4−} trigonal antiprisms and interlinked [Nd{sub 4}OS{sub 3}]{sup 4+} cubane-like clusters. Oxygen atoms were found to be trapped by Nd{sub 4} clusters in the [Nd{sub 4}OS{sub 3}]{sup 4{sub +}} chains. Structural differences among Nd{sub 4}MnOSe{sub 6}-type Nd{sub 4}FeOS{sub 6} and the related La{sub 3}CuSiS{sub 7}− and Pr{sub 8}CoGa{sub 3}-type structures have been described. Magnetic susceptibility measurements on Nd{sub 4}FeOS{sub 6} suggested the dominance of antiferromagnetic interactions at low temperature, but no magnetic ordering down to 2 K was observed. Spin-polarized electronic structure calculations revealed magnetic frustration with dominant antiferromagnetic interactions. - Graphical abstract: Trapping of oxygen in Nd{sub 4} tetrahedral clusters results in the formation of the Nd{sub 4}MnOSe{sub 6}-type Nd{sub 4}FeOS{sub 6}, in contrast to the La{sub 3}CuSiS{sub 7}-type oxygen-free Nd{sub 4}FeS{sub 7} and related Pr{sub 8}CoGa{sub 3}-type structures. Complex magnetic frustration inhibits magnetic ordering at low temperature. - Highlights: • Single crystals of Nd{sub 4}FeOS{sub 6} were grown using self-flux method. • Oxygen was found trapped by Nd{sub 4} tetrahedral clusters. • Comparison with two closely related structural types were discussed. • Magnetic measurements revealed antiferromagnetic (AFM) interaction. • VASP calculations confirmed strong magnetic frustration in AFM model.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗