Three-dimensional Magnetic Ordering Research Articles

Effect of magnetic order on longitudinal Tomonaga-Luttinger liquid spin dynamics in weakly coupled spin- 12 chains

The quantum many-body interactions in one-dimensional spin-$\frac{1}{2}$ systems are subject to Tomonaga-Luttinger liquid (TLL) physics, which predict an array of multiparticle excitations that form continua in momentum-energy space. Here we use inelastic neutron spectroscopy to study the TLL spin dynamics in ${\mathrm{SrCo}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$, a compound which contains weakly coupled spin-$\frac{1}{2}$ chains of Co atoms, at 0.05 K and in a longitudinal magnetic field up to 9.0 T. The measurements were performed above 3.9 T, where the ground-state N\'eel antiferromagnetic (AFM) order is completely suppressed and the multiparticle excitations are exclusively of the TLL type. In this region and below 7.0 T, the longitudinal TLL mode---psinon/antipsinon (P/AP)---is unexpectedly well described by a damped harmonic oscillator (DHO) while approaching the zone center defining the static spin-spin correlations. A non-DHO-type, continuumlike signal is seen at higher fields, but deviations from the ideal one-dimensional TLL still remain. This change in the P/AP mode coincides with the phase transition between the longitudinal spin density wave (LSDW) and transverse AFM order. Inside the LSDW state, the DHO-type P/AP spectral weight increases and the linewidth broadens as the magnetic order parameter decreases. These results reveal the impact of three-dimensional magnetic order on the TLL spin dynamics; they call for beyond-mean-field treatment for the interchain exchange interactions.

Quasi-one-dimensional Ising-like antiferromagnetism in the rare-earth perovskite oxide TbScO3

The rare-earth perovskite TbScO$_3$ has been widely used as a substrate for the growth of epitaxial ferroelectric and multiferroic thin films, while its detailed low-temperature magnetic properties were rarely reported. In this paper, we performed detailed magnetization, specific heat and single crystal neutron scattering measurements, along with the crystalline electric field calculations to study the low-temperature magnetic properties of TbScO$_3$. All our results suggest the magnetic Tb$^{3+}$ has an Ising-like pseudo-doublet ground state at low temperatures. Due to the constrain of local point symmetry, these Tb$^{3+}$ Ising moments are confined in the $ab$ plane with a tilt angle of $\varphi = \pm48^{\mathrm{o}}$ to the $a$ axis. In zero field, the system undergoes an antiferromagnetic phase transition at $T_{\mathrm{N}}=2.53$ K, and forms a $G_xA_y$ noncollinear magnetic structure below $T_{\mathrm{N}}$. We find the dipole-dipole interactions play an important role to determine the magnetic ground state, which are also responsible for the quasi-one-dimensional magnetism in TbScO$_3$. The significant anisotropic diffuse scatterings further confirm the quasi-one-dimensional magnetism along the $c$ axis. The magnetic phase diagram with the field along the easy $b$ axis is well established. In addition to the $G_xA_y$ antiferromagnetic state, there is an exotic field-induced phase emerged near the critical field $B_{\mathrm{c}}\simeq0.7$ T, where three-dimensional magnetic order is suppressed but strong one-dimensional correlations may still exist.

Ab initio investigation of the magnetic and ferroelectric properties of BaCuF4 under hydrostatic pressure

We present a first-principles investigation of the magnetic and ferroelectric properties of ${\mathrm{BaCuF}}_{4}$. Our calculations indicate that the magnetic topology is one-dimensional, with a N\'eel temperature smaller than 1 K, if existing. We also show that applying high-pressure values up to 40 GPa on ${\mathrm{BaCuF}}_{4}$ does not induce three-dimensional magnetic order. In addition, our calculations predict that the polar phase is destabilized under pressure. The first consequence is to reduce the energy barrier between $Cmc{2}_{1}$ polar and $Cmcm$ nonpolar phases, enhancing the ability to reverse the polarization. The second consequence is the disappearance of ferroelectricity above a critical pressure of 12.6 GPa.

Linear magnetoelastic coupling and magnetic phase diagrams of the buckled-kagomé antiferromagnet [Formula: see text

Single crystals of Cu_3Bi(SeO_3)_2O_2Cl were investigated using high-resolution capacitance dilatometry in magnetic fields up to 15 T. Pronounced magnetoelastic coupling is found upon evolution of long-range antiferromagnetic order at T_{mathrm {N}} = 26.4(3) K. Grüneisen analysis reveals moderate effects of uniaxial pressure on T_{mathrm {N}}, of 1.8(4) K/GPa, -0.62(15) K/GPa and 0.33(10) K/GPa for p parallel a, b, and c, respectively. Below 22 K Grüneisen scaling fails which implies the presence of competing interactions. The structural phase transition at T_{mathrm {S}} = 120.7(5) K is much more sensitive to uniaxial pressure than T_{mathrm {N}}, with strong effects of up to 27(3) K/GPa (p parallel c). Magnetostriction and magnetization measurements reveal a linear magnetoelastic coupling for Bparallel c below T_{mathrm {N}}, as well as a mixed phase behavior above the tricritical point around 0.4 T. An analysis of the critical behavior in zero-field points to three-dimensional (3D) Ising-like magnetic ordering. In addition, the magnetic phase diagrams for fields along the main crystalline axes are reported.

ХАЛДЕЙНОВСКИЕ ЦЕПОЧКИ

In a number of quasi-one-dimensional magnets, transition metal ions obeying the motives of the crystal lattice can form chains of integer spins that are distant from each other, named Haldane chains. This paper provides a brief overview of the magnetic properties of Haldane chains and considers some compounds containing such chains. The main features of the S=1 spin chain are that it has an unordered ground state with a finite correlation length and a spin gap in the magnetic excitation spectrum. In this paper, the manifestation of these properties is considered on the example of some compounds containing chains of Ni2+ ions (S=1). The disappearance of the spin gap and the establishment of antiferromagnetic ordering can lead to inter-chain interaction (as is the case in CsNiCl3), as well as an external magnetic field (in the case of Ni(C5H14N2)2N3(ClO4)), in which the Zeeman splitting of the Haldane triplet state occurs. To date, PbNi2V2O8 is the only known compound, in which the long-range magnetic order is induced by non-magnetic dilution of S=1 chains. In contrast to the above-listed compounds, Y2BaNiO5 remains disordered down to 0.1 K. When the non-magnetic Y3+ ion in Y2BaNiO5 is replaced by the rare earth ion R3+, a three-dimensional magnetic ordering occurs in the system. However, the Haldane gap in the spectrum of magnetic excitations of nickel is preserved both in the paramagnetic region and in the ordered state. In the ordered state, there is a paradoxical coexistence of the Haldane phase and spin waves, and the ordering occurs in the rare-earth subsystem, while the nickel subsystem remains internally disordered.

Development of short and long-range magnetic order in the double perovskite based frustrated triangular lattice antiferromagnet Ba_{2}MnTeO_{6}

Frustrated magnets based on oxide double perovskites offer a viable ground wherein competing magnetic interactions, macroscopic ground state degeneracy and complex interplay between emergent degrees of freedom can lead to correlated quantum phenomena with exotic excitations highly relevant for potential technological applications. By local-probe muon spin relaxation (muSR) and complementary thermodynamic measurements accompanied by first-principles calculations, we here demonstrate novel electronic structure and magnetic phases of Ba_{2}MnTeO_{6}, where Mn^{2+} ions with S = 5/2 spins constitute a perfect triangular lattice. Magnetization results evidence the presence of strong antiferromagnetic interactions between Mn^{2+} spins and a phase transition at T_{N} = 20 K. Below T_{N}, the specific heat data show antiferromagnetic magnon excitations with a gap of 1.4 K, which is due to magnetic anisotropy. muSR reveals the presence of static internal fields in the ordered state and short-range spin correlations high above T_{N}. It further unveils critical slowing-down of spin dynamics at T_{N} and the persistence of spin dynamics even in the magnetically ordered state. Theoretical studies infer that Heisenberg interactions govern the inter- and intra-layer spin-frustration in this compound. Our results establish that the combined effect of a weak third-nearest-neighbour ferromagnetic inter-layer interaction (owing to double-exchange) and intra-layer interactions stabilizes a three-dimensional magnetic ordering in this frustrated magnet.

Experimental observation of quantum many-body excitations of E8 symmetry in the Ising chain ferromagnet CoNb2O6

Close to the quantum critical point of the transverse-field Ising spin-chain model, an exotic dynamic spectrum was predicted to emerge upon a perturbative longitudinal field. The dynamic spectrum consists of eight particles and is governed by the symmetry of the $E_8$ Lie algebra. Here we report on high-resolution terahertz spectroscopy of quantum spin dynamics in the ferromagnetic Ising-chain material CoNb$_2$O$_6$. At 0.25 K in the magnetically ordered phase we identify characteristics of the first six $E_8$ particles, $\mathbf{m}_1$ to $\mathbf{m}_6$, and the two-particle ($\mathbf{m}_1+\mathbf{m}_2$) continuum in an applied transverse magnetic field of $B_c^{1D}=4.75$ T, before the three-dimensional magnetic order is suppressed above $B_c^{3D}\approx 5.3$ T. The observation of the higher-energy particles ($\mathbf{m}_3$ to $\mathbf{m}_6$) above the low-energy two-particle continua features quantum many-body effects in the exotic dynamic spectrum.

Phosphine-free synthesis of FeTe2 nanoparticles and self-assembly into tree-like nanoarchitectures**Project supported by the National Natural Science Foundation of China (Grant No. 11874027) and the China Postdoctoral Science Foundation (Grant Nos. 2019T120233 and 2017M621198).

Manipulating the self-assembly of transition metal telluride nanocrystals (NCs) creates opportunities for exploring new properties and device applications. Iron ditelluride (FeTe2) has recently emerged as a new class of magnetic semiconductor with three-dimensional (3D) magnetic ordering and narrow band gap structure, yet the self-assembly of FeTe2 NCs has not been achieved. Herein, the tree-like FeTe2 nanoarchitectures with orthorhombic crystal structure have been successfully synthesized by hot-injection solvent thermal approach using phosphine-free Te precursor. The morphology, size, and crystal structure have been investigated using transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and powder x-ray diffraction (XRD). We study the formation process of tree-like FeTe2 NCs according to trace the change of the sample morphology with the reaction time. It was found that the FeTe2 nanoparticles show oriented aggregation and self-assembly behavior with the increase of reaction time, which is attributed to size-dependent magnetism properties of the samples. The magnetic interaction is thought to be the driving force of nanoparticle self-organization.

Tuning the Néel Temperature of Hexagonal Ferrites by Structural Distortion.

To tune the magnetic properties of hexagonal ferrites, a family of magnetoelectric multiferroic materials, by atomic-scale structural engineering, we studied the effect of structural distortion on the magnetic ordering temperature (T_{N}) in these materials. Using the symmetry analysis, we show that unlike most antiferromagnetic rare-earth transition-metal perovskites, a larger structural distortion leads to a higher T_{N} in hexagonal ferrites and manganites, because the K_{3} structural distortion induces the three-dimensional magnetic ordering, which is forbidden in the undistorted structure by symmetry. We also revealed a near-linear relation between T_{N} and the tolerance factor and a power-law relation between T_{N} and the K_{3} distortion amplitude. Following the analysis, a record-high T_{N} (185K) among hexagonal ferrites was predicted in hexagonal ScFeO_{3} and experimentally verified in epitaxially stabilized films. These results add to the paradigm of spin-lattice coupling in antiferromagnetic oxides and suggests further tunability of hexagonal ferrites if more lattice distortion can be achieved.

Coupling of phonons with orbital dynamics and magnetism in CuSb2O6

Strongly interacting phonons and orbital excitations are observed in the same energy range for CuSb$_2$O$_6$, unlocking a so-far unexplored type of electron-phonon interaction. An orbital wave at $\sim 550$ cm$^{-1}$ softens on warming and strongly interferes with a phonon at $\sim 500$ cm$^{-1}$, giving rise to a merged excitation of mixed character. An electronic continuum grows on warming to the orbital ordering temperature $T_{OO}$=400 K, generating an important phonon decay channel. This direct and simultaneous observation of orbital and vibrational excitations reveals details of their combined dynamics. In addition, phonon frequency anomalies due to magnetic correlations are observed below $\sim 150$ K, much above the three-dimensional magnetic ordering temperature $T_N^{3D}=8.5$ K, confirming one-dimensional magnetic correlations along Cu-O-O-Cu linear chains in the paramagnetic state.

La139 NMR investigation of the charge and spin order in a La1.885Sr0.115CuO4 single crystal

$^{139}\mathrm{La}$ NMR is suited for investigations into magnetic properties of ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$-based cuprates in the vicinity of their magnetic instabilities, owing to the modest hyperfine interactions between $^{139}\mathrm{La}$ nuclear spins and Cu electron spins. We report comprehensive $^{139}\mathrm{La}$ NMR measurements on a single-crystal sample of high-${T}_{c}$ superconductor ${\mathrm{La}}_{1.885}{\mathrm{Sr}}_{0.115}{\mathrm{CuO}}_{4}$ in a broad temperature range across the charge and spin order transitions $({T}_{\mathrm{charge}}\ensuremath{\simeq}80$ K, ${T}_{\mathrm{spin}}^{\mathrm{neutron}}\ensuremath{\simeq}{T}_{c}=30$ K). From the high-precision measurements of the linewidth for the nuclear spin ${I}_{z}=+1/2$ to $\ensuremath{-}1/2$ central transition, we show that paramagnetic line broadening sets in precisely at ${T}_{\mathrm{charge}}$ due to enhanced spin correlations within the ${\mathrm{CuO}}_{2}$ planes. Additional paramagnetic line broadening ensues below $\ensuremath{\sim}35$ K, signaling that Cu spins in some segments of ${\mathrm{CuO}}_{2}$ planes are on the verge of three-dimensional magnetic order. A static hyperfine magnetic field arising from ordered Cu moments along the $ab$ plane, however, begins to develop only below ${T}_{\mathrm{spin}}^{\ensuremath{\mu}SR}=15--20$ K, where earlier muon spin rotation measurements detected Larmor precession for a small volume fraction $(\ensuremath{\sim}20%)$ of the sample. Based on the measurement of $^{139}\mathrm{La}$ nuclear-spin-lattice relaxation rate $1/{T}_{1}$, we also show that charge order triggers enhancement of low-frequency Cu spin fluctuations inhomogeneously; a growing fraction of $^{139}\mathrm{La}$ sites is affected by enhanced low-frequency spin fluctuations toward the eventual magnetic order, whereas a diminishing fraction continues to exhibit a behavior analogous to the optimally superconducting phase even below ${T}_{\mathrm{charge}}$. These $^{139}\mathrm{La}$ NMR results corroborate our recent $^{63}\mathrm{Cu}$ NMR observation that a very broad, anomalous winglike signal gradually emerges below ${T}_{\mathrm{charge}}$, whereas the normally behaving, narrower main peak is gradually wiped out [T. Imai et al., Phys. Rev. B 96, 224508 (2017)]. Furthermore, we show that the enhancement of low-energy spin excitations in the low-temperature regime below ${T}_{\mathrm{spin}}^{\mathrm{neutron}}\phantom{\rule{4pt}{0ex}}(\ensuremath{\simeq}{T}_{c})$ depends strongly on the magnitude and orientation of the applied magnetic field.

Quasi-2D Heisenberg Antiferromagnets [CuX(pyz)2](BF4) with X = Cl and Br.

Two Cu2+ coordination polymers [CuCl(pyz)2](BF4) 1 and [CuBr(pyz)2](BF4) 2 (pyz = pyrazine) were synthesized in the family of quasi two-dimensional (2D) [Cu(pyz)2]2+ magnetic networks. The layer connectivity by monatomic halide ligands results in significantly shorter interlayer distances. Structures were determined by single-crystal X-ray diffraction. Temperature-dependent X-ray diffraction of 1 revealed rigid [Cu(pyz)2]2+ layers that do not expand between 5 K and room temperature, whereas the expansion along the c-axis amounts to 2%. The magnetic susceptibility of 1 and 2 shows a broad maximum at ∼8 K, indicating antiferromagnetic interactions within the [Cu(pyz)2]2+ layers. 2D Heisenberg model fits result in J∥ = 9.4(1) K for 1 and 8.9(1) K for 2. The interlayer coupling is much weaker with | J⊥| = 0.31(6) K for 1 and 0.52(9) K for 2. The electron density, experimentally determined and calculated by density functional theory, confirms the location of the singly occupied orbital (the magnetic orbital) in the tetragonal plane. The analysis of the spin density reveals a mainly σ-type exchange through pyrazine. Kinks in the magnetic susceptibility indicate the onset of long-range three-dimensional magnetic order below 4 K. The magnetic structures were determined by neutron diffraction. Magnetic Bragg peaks occur below TN = 3.9(1) K for 1 and 3.8(1) K for 2. The magnetic unit cell is doubled along the c-axis ( k = 0, 0, 0.5). The ordered magnetic moments are located in the tetragonal plane and amount to 0.76(8) μB/Cu2+ for 1 and 0.6(1) μB/Cu2+ for 2 at 1.5 K. The moments are coupled antiferromagnetically both in the ab plane and along the c-axis. The Cu2+ g-tensor was determined from electron spin resonance spectra as g x = 2.060(1), g z = 2.275(1) for 1 and g x = 2.057(1), g z = 2.272(1) for 2 at room temperature.

Spin-reorientation transitions in the Cairo pentagonal magnet Bi4Fe5O13F

We show that interlayer spins play a dual role in the Cairo pentagonal magnet Bi$_4$Fe$_5$O$_{13}$F, on one hand mediating the three-dimensional (3D) magnetic order and on the other driving spin-reorientation transitions both within and between the planes. The corresponding sequence of magnetic orders unraveled by neutron diffraction and M\"ossbauer spectroscopy features two orthogonal magnetic structures described by opposite local vector chiralities, and an intermediate, partly disordered phase with nearly collinear spins. A similar collinear phase has been predicted theoretically to be stabilized by quantum fluctuations, but Bi$_4$Fe$_5$O$_{13}$F is very far from the relevant parameter regime. While the observed in-plane reorientation cannot be explained by any standard frustration mechanism, our ab initio band-structure calculations reveal strong single-ion anisotropy of the interlayer Fe$^{3+}$ spins that turns out to be instrumental in controlling the local vector chirality and the associated interlayer order.

Complex Three-Dimensional Magnetic Ordering in Segmented Nanowire Arrays.

A comprehensive three-dimensional picture of magnetic ordering in high-density arrays of segmented FeGa/Cu nanowires is experimentally realized through the application of polarized small-angle neutron scattering. The competing energetics of dipolar interactions, shape anisotropy, and Zeeman energy in concert stabilize a highly tunable spin structure that depends heavily on the applied field and sample geometry. Consequently, we observe ferromagnetic and antiferromagnetic interactions both among wires and between segments within individual wires. The resulting magnetic structure for our nanowire sample in a low field is a fan with magnetization perpendicular to the wire axis that aligns nearly antiparallel from one segment to the next along the wire axis. Additionally, while the low-field interwire coupling is ferromagnetic, application of a field tips the moments toward the nanowire axis, resulting in highly frustrated antiferromagnetic stripe patterns in the hexagonal nanowire lattice. Theoretical calculations confirm these observations, providing insight into the competing interactions and resulting stability windows for a variety of ordered magnetic structures. These results provide a roadmap for designing high-density magnetic nanowire arrays for spintronic device applications.

In Situ Generation of NiO Nanoparticles in a Magnetic Metal–Organic Framework Exhibiting Three-Dimensional Magnetic Ordering

NiO nanoparticles were in situ formed in a new metal-organic framework (MOF), [Ni3(pyip)2(HCOO)2(H2O)2]n [1; H2pyip = 5-(pyridine-4-yl)isophthalic acid], which was characterized by Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, transmission electron microscopy, and powder and single-crystal X-ray diffraction. The MOF 1 shows a 3,6-connected three-dimensional rtl topology network with a topological symbol of (4.62)2(42.610.83). Magnetic property studies showed that the combination of NiO nanoparticles within the magnetic MOF leads to the occurrence of long-range magnetic ordering below a critical temperature of 18 K.

Magnetic properties of the covalent chain antiferromagnetRbFeSe2

Single crystals of the ternary iron selenide ${\mathrm{RbFeSe}}_{2}$ have been investigated by means of x-ray diffraction, magnetic susceptibility, magnetization, and specific-heat measurements as well as by M\ossbauer spectroscopy. Built up from linear chains of edge-sharing ${\mathrm{FeSe}}_{4}$ tetrahedra, ${\mathrm{RbFeSe}}_{2}$ represents a quasi-one-dimensional antiferromagnet. Below ${T}_{\mathrm{N}}=248$ K three-dimensional antiferromagnetic collinear magnetic order sets in, with the magnetic moments oriented perpendicularly to the chain direction. The hyperfine fields determined from our M\ossbauer studies reveal strongly reduced magnetic moments. The high-temperature susceptibility data of ${\mathrm{RbFeSe}}_{2}$ suggest a one-dimensional metallic character along the chains.

Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr2IrO4.

Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity. Recently, photo-excitation has been used to induce similarly exotic states transiently. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr2IrO4. We find that the non-equilibrium state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. The marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.

Neutron Powder Diffraction study of the Magnetic Ionic Liquid Emim[FeCL4] and its deuterated phase

A magnetic ionic liquid comprising 1-ethyl-3 methylimidazolium (Emim) cations and tetraclhoroferrate(III) (FeCl4) anions and its deuterated phase were synthetized and characterized magnetically. In both materials, the low temperature dependence of the magnetic susceptibility presents a maximum (around 4 K) related to an antiferromagnetic ordering, but the ordering temperatures are slightly shifted and the curves display different shapes. In addition, the magnetization of the deuterated phase tends to saturate at higher values than that corresponding to the non-deuterated analogue. A comparison of the neutron diffraction patterns above and below the magnetic transition clearly shows that the crystal and magnetic structures of these materials are different. Therefore, the present findings clearly prove that the magnetic exchange interactions that induce three-dimensional magnetic ordering are modified after the deuteration process.

Synthesis and physical properties of quasi-one-dimensional magnetic material Ca3LiRuO6

Ca 3 LiRuO 6 single crystals were grown using the flux method, magnetic properties measurement results along different directions of needle-like single crystals are reported for the first time and show Ca 3 LiRuO 6 occurs a paramagnetic (PM)-weak ferromagnetic (FM) transition at a temperature Tc = 120 K , also the magnetic moment aligns in the ab plane. Although Ca 3 LiRuO 6 is characterized by one-dimensional configuration in crystallographic structure, it has three-dimensional (3D) magnetic order, the value of Tc is far below the magnitude of Curie–Weiss temperature. Θcw ≈ -306 K indicates complex nature of the magnetism is in this compound.

The phase diagram of electron-doped La(2-x)Ce(x)CuO(4-δ).

Superconductivity is a striking example of a quantum phenomenon in which electrons move coherently over macroscopic distances without scattering. The high-temperature superconducting oxides (cuprates) are the most studied class of superconductors, composed of two-dimensional CuO2 planes separated by other layers that control the electron concentration in the planes. A key unresolved issue in cuprates is the relationship between superconductivity and magnetism. Here we report a sharp phase boundary of static three-dimensional magnetic order in the electron-doped superconductor La(2-x)Ce(x)CuO(4-δ), where small changes in doping or depth from the surface switch the material from superconducting to magnetic. Using low-energy spin-polarized muons, we find that static magnetism disappears close to where superconductivity begins and well below the doping level at which dramatic changes in the transport properties are reported. These results indicate a higher degree of symmetry between the electron and hole-doped cuprates than previously thought.