Coexistence Of Long-range Antiferromagnetic Order Research Articles

Effect of antiferromagnetic order on topological electronic structure in Eu-substituted Bi2Se3 single crystals

Topological antiferromagnetic spintronics is an emerging field due to advantages such as no stray field effect and high-speed dynamics. In bismuth chalcogenide topological insulators, the coexistence of long-range antiferromagnetic order and topologically protected states has scarcely been observed. Here, an antiferromagnetic order, which sets in the direction of magnetic moments perpendicular to the c axis, is introduced by Eu substitution in Bi2Se3, and therefore it influences the topological electronic properties of Bi2Se3. Despite Eu substitution, Shubnikov–de Haas (SdH) oscillations are observed. The angle dependence of SdH oscillations shows a signature of anisotropic 3D Fermi surfaces with a nontrivial Berry phase by Eu substitution, and the temperature dependence of SdH oscillations reveals that the effective mass is comparable to the pristine Bi2Se3. These results suggest that the nontrivial topological state can survive in the antiferromagnetic order of Eu-substituted Bi2Se3. Our work expands the base of topological materials available for antiferromagnetic spintronics applications.

Anisotropic fluoride nanocrystals modulated by facet-specific passivation and their disordered surfaces

Rutile-type fluorides have been proven to be active components in the context of emerging antiferr-omagnetic devices. However, controlled synthesis of low-dimensional, in particular two-dimensional (2D), fluorides in a predictable and deterministic manner remains unrealized because of a lack of efficient anisotropic control, which impedes their further development in reduced dimensions. We report here that altered passivation of {110} growing facets can direct the synthesis of rutile-type fluoride nanocrystals into well-defined zero-dimensional (0D) particulates, one-dimensional (1D) rods and 2D sheets in a colloidal approach. The obtained nanocrystals show positive exchange bias and enhanced magnetic transition temperature from the coexistence of long-range antiferromagnetic order and disordered surface spins, making them strong alternatives for flexible magnetic devices and sensors.

Coexistence of long-range antiferromagnetic order and slow relaxation of the magnetization in the first lanthanide complex of a 1,2,4-benzotriazinyl radical.

The first lanthanide complex of a 1,2,4-benzotriazinyl radical (1), Dy(1)(tbacac)3 (2, tbacac = 2,2,6,6-tetramethyl-3,5-heptane-dionato), was synthesised and found to have an antiferromagnetically ordered ground state with a metamagnetic phase diagram and a critical field of 0.91 T at 1.85 K. The application of a small dc field revealed the single-molecule magnet behaviour of 2, illustrating the coexistence of long-range antiferromagnetic order and slow relaxation of the magnetization.

Incommensurate spin-density-wave order in quasi-one-dimensional metallic antiferromagnetNaV2O4

To clarify the reason for the coexistence of long-range antiferromagnetic order and metallic conductivity for ${\text{NaV}}_{2}{\text{O}}_{4}$, in which the V ions form quasi-one-dimensional zigzag chains along the $b$ axis, we have performed a neutron-scattering experiment using a powder sample down to 20 K. The analysis of the magnetic powder diffractogram below ${T}_{\text{N}}=140\text{ }\text{K}$ demonstrates the formation of an incommensurate spin-density-wave order with $\mathbit{k}=(0,0.191,0)$; the ordered moment was estimated as $(0,0,0.77{\ensuremath{\mu}}_{\text{B}})$ at 20 K.

Superconductivity and the spin-triplet collective mode in thet−Jmodel close to antiferromagnetic instability

To investigate relations between long-range antiferromagnetic (AF) order, superconductivity and two-particle triplet collective excitations we consider a modified two dimensional $t\ensuremath{-}J$ model at doping close to half filling. The model includes additional hopping ${J}^{\ensuremath{''}}$ and nearest sites Coulomb repulsion V. The additional parameters allow us to control closeness of the system to the AF instability. We demonstrate the possibility of coexistence of long-range AF order and $d\ensuremath{-}g$-wave superconductivity. In the phase with long-range AF order we find, analytically, superconducting gaps and spin-wave renormalization. We demonstrate that at approaching the point of the AF instability the spin-triplet collective excitation arises with energy below the superconducting gap.

Microstructure and Magnetization Investigations of Cu-Doping Effect on La2CuO4+δ Crystal

Measurement and characterization were carried out on Cu-doped and undoped La2CuO4+δ samples prepared under the same conditions. The magnetization measurement on the Cu-doped La2CuO4+δ sample shows coexistence of long-range antiferromagnetic order and superconductivity. A stripe-like structure was observed at room temperature on the ab-plane of Cu-doped La2CuO4+δ sample by transmission electron microscope. While for the undoped La2CuO4+δ sample no such behavior or structure feature was found. In this letter, these phenomena were discussed in terms of phase separation.

Dynamic short-range order observed in the (Zn)[Fe2]O4 spinel by neutron diffraction, μSR, and Mössbauer experiments

Using neutron diffraction (ND), muon-spin rotation/relaxation (μSR), and57Fe-Mossbauer spectroscopy (MS) we have investigated magnetic properties of the normal spinel (Zn)[Fe2]O4. In compounds which are slowly cooled from 1200°C to room temperature inversion is below detection limits. AtT N = 10.5 K the spinel exhibits long-range antiferromagnetic order (LRO). The transition as seen in thermal-scan spectra by MS is very sharp. However, ND andμSR experiments show that already at temperatures of ∼ 10T N a short-range antiferromagnetic ordering (SRO) develops which extends through ∼70% of the sample volume just aboveT N . BelowT N SRO and LRO coexist. At 4.2 K still ∼25% of the sample is short-range ordered. The regions over which the SRO extends have a size of ∼ 3 nm. Their fluctuation rates are in the GHz range. Modern ab initio cluster calculations successfully describe the magnetic hyperfine fields as well as the electric field gradient (EFG) tensor at the Fe sites. Covalency of the Fe-O and Zn-O bonds is important. The physical origin of the regions exhibiting SRO, however, remains unresolved at this point.

Magnetic properties of the ZnFe2O4 spinel.

Using neutron diffraction (ND), muon-spin rotation/relaxation ($\ensuremath{\mu}\mathrm{SR}$), and $^{57}\mathrm{Fe}$ and $^{67}\mathrm{Zn}$ M\ossbauer spectroscopy (MS) we investigated magnetic properties of the normal spinel Zn${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$. Inversion is below limits of detection in samples which were slowly cooled from 1200 \ifmmode^\circ\else\textdegree\fi{}C to room temperature. Below ${T}_{N}=10.5$ K the spinel exhibits long-range antiferromagnetic order (LRO). However, already at temperatures of about $T\ensuremath{\approx}10{T}_{N}$ a short-range antiferromagnetic order (SRO) develops which extends through \ensuremath{\approx}70% of the sample volume just above ${T}_{N}$. Below ${T}_{N}$ antiferromagnetic SRO and LRO coexist. At 4.2 K still \ensuremath{\approx}20% of the sample are short-range ordered. The regions exhibiting SRO are very small (\ensuremath{\approx}3 nm). Their fluctuation rates as estimated from $\ensuremath{\mu}\mathrm{SR}$ are in the GHz range. For this reason the SRO above ${T}_{N}$ remains hidden in MS and is only seen in ND and $\ensuremath{\mu}\mathrm{SR}$ with their more appropriate time windows. Although the physical origin of the SRO remains an enigma, our experiments show that it is not caused by partial inversion but rather is an intrinsic property of Zn${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$. Modern ab initio cluster calculations successfully describe the magnetic hyperfine field as well as the electric field gradient tensor at the Fe site as seen by MS.

Nature of the magnetic order in superconducting and nonsuperconducting HoNi2-xCoxB2C.

Neutron-diffraction measurements have been carried out to investigate the magnetic properties of superconducting (${\mathit{T}}_{\mathit{c}}$\ensuremath{\sim}8 K) ${\mathrm{HoNi}}_{2}$${\mathrm{B}}_{2}$C and nonsuperconducting (${\mathit{T}}_{\mathit{c}}$3 K) ${\mathrm{HoNi}}_{1.985}$${\mathrm{Co}}_{0.015}$${\mathrm{B}}_{2}$C. Both systems become magnetically long-range ordered below \ensuremath{\sim}8 K, with three types of magnetic order being present. The low-temperature structure is a commensurate antiferromagnetic state that consists of ${\mathrm{Ho}}^{3+}$ moments aligned ferromagnetically in the a-b plane, with the sheets coupled antiferromagnetically along the c axis. The magnetic state that initially forms on cooling, however, is dominated by an incommensurate spiral antiferromagnetic state along the c axis, with wave vector ${\mathit{q}}_{\mathit{c}}$\ensuremath{\approxeq}0.054 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$, in which the relative alignment of each ferromagnetic sheet is rotated in the a-b plane by \ensuremath{\sim}17\ifmmode^\circ\else\textdegree\fi{} from the low-temperature antiparallel configuration. The intensity for this spiral state reaches a maximum near \ensuremath{\sim}5 K; the spiral state then collapses at lower temperature in favor of the commensurate antiferromagnetic state. A smaller amplitude a-axis modulation, with ${\mathit{q}}_{\mathit{a}}$\ensuremath{\approxeq}0.73 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$, is also observed above the spiral antiferromagnetic transition, but over a narrower temperature range than the spiral state. The identical sequence of phase transitions is observed for both the superconducting and nonsuperconducting samples, demonstrating that the reentrant superconductivity and the coexistence of long-range antiferromagnetic order and superconductivity at low temperatures are both controlled by the nature of the magnetic structures present. In the temperature regime where the three magnetic structures are observed simultaneously, the sample dependence of the intensities strongly suggests that they occur in spatially separate regions. \textcopyright{} 1996 The American Physical Society.

HEAVY FERMIONS — THEIR MAGNETISM AND SUPERCONDUCTIVITY

Heavy-fermion compounds are ideally suited to study cooperative phenomena in highly correlated electron systems. We discuss local-moment magnetism and heavy-fermion band magnetism in the exemplary systems CeCu 2 Ge 2 and Ni-rich Ce(Cu 1− x Ni x )2 Ge 2, respectively. In addition, the coexistence of long-range antiferromagnetic order and heavy-fermion superconductivity in UM 2 Al 3 (M: Ni, Pd) will be addressed.

Coexistence of superconductivity and antiferromagnetic order in SmRh 4B 4

The ternary rare earth compound SmRh 4B 4 has been studied by means of upper critical field, low temperature specific heat, and static magnetic susceptibility measurements. A lambda-type specific heat anomaly, a discontinuity in the slope of the upper critical field versus temperature curve, and a cusp-like feature in the magnetic susceptibility suggest that superconductivity and long-range antiferromagnetic order coexist in SmRh 4B 4 below 0.87 K. Machida's theory for antiferromagnetic superconductors provides a good description of the upper critical field data, while the magnetic susceptibility data can be represented as the sum of a Curie-Weiss term with micro eff = 0.632 micro B and θ p = −1.93 K and a temperature independent Van Vleck contribution.

Coexistence of superconductivity and long-range antiferromagnetic order in the compound Er xMo 6Se 8

Low temperature specific heat and magnetic susceptibility measurements indicate that superconductivity and long-range antiferromagnetic order coexist in the compound Er xMo 6Se 8 ( x = 1.0 and 1.2).