Spin Canting Research Articles

Transition of topological Hall effect for tetragonal Heusler Mn2PtSn thin film

A large topological Hall effect was observed in Mn2PtSn epitaxial thin films. The non-hysteretic topological Hall resistivity can be attributed to the canted spins below the reorientation temperature, while the hysteretic topological resistivity in the vicinity of the zero field captures the trend of antiskyrmion formation. A decrease in thickness enhances the contribution of dipolar interactions, leading to an additional antiskyrmion-type signal above the reorientation temperature. The amplitudes of these topological signals are strongly modulated by the film thickness, providing pathways for developing antiskyrmion-hosting media via film engineering.

Magnetic properties of multiferroic Pb5Fe3F19

Fluoride ferroelectrics containing 3d transition metal ions are potential single-phase multiferroics. Pure phase Pb5Fe3F19 powders are prepared by the solid-state reaction, which is confirmed by the X-ray diffraction with isostructure to Pb5Cr3F19. X-ray photoelectron spectroscopy confirms that Fe ions are in the valence state of +3. Ferroelectricity is confirmed by the observation of amplitude and phase hysteresis loops by piezoresponse force microscopy at room temperature. Two anomalies are observed at TN1 of 78 K and TN2 of 21 K in the temperature dependent magnetization (M−T) curves, which is due to the onset of two antiferromagnetic transitions. The bifurcation between the zero-field cooled and field cooled M−T curves at temperatures below TN1 of 78 K is attributed to competition of the complicated antiferromagnetic exchange coupling between the neighboring Fe3+ ions, leading to the magnetic relaxation. Small hysteresis with negligible coercivity can be observed in the field dependent magnetization curves below TN1. The magnetization and coercivity are significantly enhanced with further decreasing temperature, indicating the weak ferromagnetism. The observed ferromagnetism might be due to the magnetoelectric coupling between the ferroelectric polarization and magnetization, leading to the spin canting of the antiferromagnetic coupling between neighboring Fe3+ ions. The magnetoelectric coupling is confirmed by the observation of magnetodielectric effect, which is due to the strong magnetic and structural coupling.

Unusual cation coordination in nanostructured mullites

Abstract Nanocrystalline mullite-type bismuth-bearing complex oxides Bi2(M0.5Al0.5)4O9 (M=Fe3+, Ga3+) are prepared by high-energy ball milling of the corresponding microcrystalline counterparts. An unusual five-fold coordination of metal cations is revealed in nanostructured Bi2(M0.5Al0.5)4O9 by means of 27Al magic angle spinning nuclear magnetic resonance and 57Fe Mössbauer spectroscopies. The concentration of five-fold coordinated cations increases with decreasing crystallite size of a material at the expense of octahedrally coordinated ones. In addition to the nuclear spectroscopic methods, Rietveld analyses of the X-ray diffraction data of the as-prepared nanooxides show that the constituent tetrahedra, octahedra, and the newly formed structural units with five-fold cation coordination are strongly distorted. With decreasing crystallite size of mullites, the average volume of their octahedra increases whereas this parameter decreases for tetrahedra. The macroscopic behaviour of the non-equilibrium nanomullites is characterised by SQUID magnetometry. The Fe-containing mullites exhibit a superposition of a dominant antiferromagnetism and a weak ferromagnetism. The increase in both the remanent magnetization and the coercive field with decreasing crystallite size is attributed to the effect of spin canting. The latter is confined to the interfacial and surface regions of the nanomaterials, and arises due to both the mechanically induced deformation of constituent structural units and the formation of cation sites with the unusual five-fold coordination.

Room temperature magnetoelectric coupling in Pb(Fe1/2Nb1/2)O3 by counterbalancing imbalanced spin moments through spin canting

In this study, ferroelectric Pb(Fe1/2Nb1/2)O3 with an antiferromagnetic polymorph at and below 150 K was converted into a room-temperature magnetoelectrically active multiferroic with soft ferromagnetism by disrupting the existing antiparallel spin alignment of Fe ions through the heavy replacement of Fe by Ni. To maximize the induced soft-ferromagnetic properties and the consequent nonlinear magnetoelectric coupling, the substitution level of Ni should be controlled such that the individual Ni ions are separated from one another to avoid mutual spin cancellation. The induced magnetoelectric coupling was found to originate from the collective contribution of oppositely canted pairs of spins in two nearby Fe3+ ions, which counterbalances the relatively smaller spin moment of the in-between Ni ions. The non-material specific nature of this strategy implies that it can be used in the development of new room-temperature multiferroic perovskite oxides.

Structure, Magnetism, and Thermal Stability of La2NiO2.5F3: A Ruddlesden-Popper Oxyfluoride Crystallizing in Space Group P42/nnm.

We report on the new Ruddlesden-Popper (RP) oxyfluoride La2NiO2.5F3 containing an unprecedented high amount of fluorine and Ni2+. This oxyfluoride was prepared by topochemical low-temperature fluorination of La2NiO4, which was obtained by a soft chemistry synthesis, with poly(vinylidene difluoride) (PVDF) as fluorinating agent. La2NiO2.5F3 is the first n = 1 RP compound crystallizing in the tetragonal space group P42/nnm (a = 5.7297(6) Å and c = 13.0106(2) Å). The crystal structure shows a unique tilting scheme of the NiO4F2 octahedra that has so far been only theoretically predicted. Combined neutron and X-ray powder diffraction experiments together with bond-valence-sum and DFT+U calculations reveal an unusual anion ordering with fluoride being located on the apical anion sites of the NiO4F2 octahedra. Excess fluorine ions were found to populate two of the four interstitial anion sites in an ordered fashion. A third interstitial anion position is occupied by oxygen ions while the fourth site remains unoccupied. This hitherto unobserved ordering scenario in RP oxyfluorides promotes a strong layerwise alternating tilting of the NiO4F2 octahedra. Magnetic measurements show strong antiferromagnetic interactions with a high Néel temperature of about 225 K and a pronounced ZFC/FC splitting most likely as the result of a small ferromagnetic moment arising from spin canting. The electronic structure was characterized by DFT and UV-vis spectroscopy, and a strong increase of Eg was found compared to La2NiO4 (3.4 eV vs 1.3 eV).

Large Hall and Nernst responses from thermally induced spin chirality in a spin-trimer ferromagnet

The long-range order of noncoplanar magnetic textures with scalar spin chirality (SSC) can couple to conduction electrons to produce an additional (termed geometrical or topological) Hall effect. One such example is the Hall effect in the skyrmion lattice state with quantized SSC. An alternative route to attain a finite SSC is via the spin canting caused by thermal fluctuations in the vicinity of the ferromagnetic ordering transition. Here, we report that for a highly conducting ferromagnet with a two-dimensional array of spin trimers, the thermally generated SSC can give rise to a gigantic geometrical Hall conductivity even larger than the intrinsic anomalous Hall conductivity of the ground state. We also demonstrate that the SSC induced by thermal fluctuations leads to a strong response in the Nernst effect. A comparison of the sign and magnitude of fluctuation-Nernst and Hall responses in fundamental units indicates the need for a momentum-space picture to model these thermally induced signals.

Effects of Ni substitution on multiferroic properties in Bi5FeTi3O15 ceramics

The single-phase multiferroic Bi5Fe1 − x Ni x Ti3O15 (BFNT-x, x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) ceramics were synthesized by a sol-gel auto-combustion method, and their microstructures, ferroelectric, magnetic, and dielectric properties were investigated in detail. All samples belong to layer-perovskited Aurivillius phase containing four perovskite units sandwiched between two Bi–O layers. Ni substitution can not only improve ferroelectricity but also enhance the magnetic properties. The BFNT-0.2 sample shows the largest remnant polarization (2P r ∼ 11.6 μC/cm2) and the highest remnant magnetization (2M r ∼ 0.244 emu/g). The enhancement of the magnetic properties may mainly originate from the spin canting of Fe/Ni-O octahedra via Dzyaloshinskii–Moriya (DM) interaction. In order to explore the influence of valance state of magnetic ions on the properties, the x-ray photoelectron spectroscopy was carried out. Furthermore, structural, ferroelectric, and magnetic transitions were also investigated.

Element-specific contributions to improved magnetic heating of theranostic CoFe2O4 nanoparticles decorated with Pd

Decoration with Pd clusters increases the magnetic heating ability of cobalt ferrite (CFO) nanoparticles by a factor of two. The origin of this previous finding is unraveled by element-specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD) combined with atomic multiplet simulations and density functional theory (DFT) calculations. While the comparison of XAS spectra with atomic multiplet simulations show that the inversion degree is not affected by Pd decoration and, thus, can be excluded as a reason for the improved heating performance, XMCD reveals two interrelated responsible sources: significantly larger Fe and Co magnetic moments verify an increased total magnetization which enhances the magnetic heating ability. This is accompanied by a remarkable change in the field-dependent magnetization particularly for Co ions which exhibit an increased low-field susceptibility and a reduced spin canting behavior in higher magnetic fields. Using DFT calculations, these findings are explained by reduced superexchange between ions on octahedral lattice sites via oxygen in close vicinity of Pd, which reinforces the dominating antiparallel superexchange interaction between ions on octahedral and tetrahedral lattice sites and thus reduces spin canting. The influence of the delocalized nature of Pd 4d electrons on the neighboring ions is discussed and the conclusions are illustrated with spin density isosurfaces of the involved ions. The presented results pave the way to design nanohybrids with tailored electronic structure and magnetic properties.

Room‐temperature multiferroicity in NiFe2O4 and its magnetoelectric coupling intensified through defect engineering

AbstractThe well‐known ferromagnetic oxide, NiFe2O4, was studied as a potential candidate for room‐temperature Type II magnetoelectrics. A spin canting as one of the essential requirements for Type II multiferroics was induced by breaking the stoichiometry, that is, intentionally subtracting Fe ions. We observed that Fe ions were first subtracted exclusively from the tetrahedral sites, leading to an increase in the magnetoelectric coupling owing to an increasing degree of spin canting. The enhancement in the magnetoelectric coupling culminated beyond the subtraction level of ~30 at.%, at which Fe ions started to be removed from the octahedral sites. Alongside, we observed that the subtraction of Fe ions gives rise to a ferroelectricity due to the formation of defect complexes that establish an internal bias field.

The impact of highly paramagnetic Gd3+ cations on structural, spectral, magnetic and dielectric properties of spinel nickel ferrite nanoparticles

In this work, fabrication of Gd3+ substituted nickel spinel ferrite (NiGdxFe2-xO4) nanoparticles was carried out via co-precipitation route. X-ray powder diffraction (XRD) confirmed the spinel cubic structure of NiGdxFe2-xO4 nanoparticles. XRD data also facilitated to determine the divalent and trivalent metal cations distribution at both A and B sites of the ferrite lattice. Site radii, hopping and bond lengths were also calculated from XRD data. The spectral studies elucidated the formation of cubic spinel ferrite structure as well as stretching vibrations of M–O (metal–oxygen) bond at A and B sites of ferrites, represented by two major bands υ1 and υ2 respectively. FESEM analysis confirmed the irregular morphology of NiGdxFe2-xO4 nanoparticles. EDX spectrographs estimated the elemental compositions. The dielectric attributes were explained on the basis of the Debye-relaxation theory and Koop’s phenomenological model. At higher applied frequencies (AC) no prominent dielectric loss was observed. Magnetic parameter variations can be attributed to the substitution of the rare earth cations having larger ionic radii as compared to the radii of Fe3+ ions. Moreover, spin canting, magneto-crystalline anisotropy and exchange energy of electrons also helped in magnetic evaluation. Due to small coercivity values NiGdxFe2-xO4 nanoparticles can be employed significantly in high-frequency data storage devices.

Magnetism in quasi-two-dimensional tri-layer La2.1Sr1.9Mn3O10 manganite

The tri-layer La_{3-3x}Sr_{1+3x}Mn_{3}O_{10} manganites of Ruddlesden–Popper (RP) series are naturally arranged layered structure with alternate stacking of ω-MnO_2 (ω = 3) planes and rock-salt type block layers (La, Sr)_2O_2 along c-axis. The dimensionality of the RP series manganites depends on the number of perovskite layers and significantly affects the magnetic and transport properties of the system. Generally, when a ferromagnetic material undergoes a magnetic phase transition from ferromagnetic to paramagnetic state, the magnetic moment of the system becomes zero above the transition temperature (T _{C} ). However, the tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10} shows non-zero magnetic moment above T _{C} and also another transition at higher temperature T ^{*} approx 263 K. The non-zero magnetization above T _{C} emphasizes that the phase transition in tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10} not a ferromagnetic to paramagnetic state. We show here the non-zero magnetic moment above T _{C} is due to the quasi-two-dimensional nature of the tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10} manganite. The scaling of the magnetic entropy change confirms the second-order phase transition and the critical behavior of phase transition has been studied around T_C to understand the low dimensional magnetism in tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10}. We have obtained the critical exponents for tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10}, which belong to the short-range two-dimensional (2D)-Ising universality class. The low dimensional magnetism in tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10} manganite is also explained with the help of renormalization group theoretical approach for short-range 2D-Ising systems. It has been shown that the layered structure of tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10} results in three different types of interactions intra-planer ( J_{ab} ), intra-tri-layer ( J_{c} ) and inter-tri-layer ( J' ) such that J_{ab}> J_{c}>> J' and competition among these give rise to the canted antiferromagnetic spin structure above T _{C} . Based on the similar magnetic interaction in bi-layer manganite, we propose that the tri-layer La_{2.1}Sr_{1.9}Mn_{3}O_{10} should be able to host the skyrmion below T _{C} due to its strong anisotropy and layered structure.

Structure and magnetic properties of the S = 3/2 zigzag spin chain antiferromagnet BaCoTe2O7

We report a study of the structure and magnetic properties of the S = 3/2 zigzag spin chain compound BaCoTe2O7. Neutron diffraction measurements show that it crystallizes in the noncentrosymmetric space group Ama2 with a canted ↑↑↓↓ spin structure along the quasi-one-dimensional zigzag chain and a moment size of 1.89(2) µB at 2 K. Both magnetic susceptibility and specific heat measurements yield an antiferromagnetic phase transition at TN = 6.2 K. A negative Curie-Weiss temperature, ΘCW = −74.7(2) K, and an empirical frustration parameter, f = ∣ΘCW∣/TN ≈ 12, are obtained by fitting the magnetic susceptibility, indicating antiferromagnetic interactions and strong magnetic frustration. From ultraviolet-visible absorption spectroscopy and first-principles calculations, an indirect band gap of 2.68(2) eV is determined. We propose that the canted zigzag spin chain of BaCoTe2O7 may produce a change in the polarization via the exchange-striction mechanism.

Field‐Driven Reversal Models in Artificial Spin Ice

AbstractA set of topological arrangements of individual ferromagnetic islands in ideal and disordered artificial spin ice (ASI) arrays is investigated in order to evaluate how aspects of their field‐driven reversal are affected by the model used. The set contains the pinwheel and square ice tilings, and thus a range of magnetic ordering and reversal properties are tested. It is found that a simple point dipole model performs relatively well for square ice, but it does not replicate the properties observed in recent experiments with pinwheel ice. Parameterization of the reversal barrier in a Stoner–Wohlfarth model improves upon this, but fails to capture aspects of the physics of ferromagnetic coupling observed in pinwheel structures which have been attributed to the non‐Ising nature of the islands. In particular, spin canting is found to be important in pinwheel arrays, but not in square ones, due to their different symmetries. The authors' findings will improve the modeling of ASI structures for fundamental research and in applications which are reliant upon the ability to obtain and switch through known states using an externally applied field.

The chiral Hall effect in canted ferromagnets and antiferromagnets

The anomalous Hall effect has been indispensable in our understanding of numerous magnetic phenomena. This concerns both ferromagnetic materials, as well as diverse classes of antiferromagnets, where in addition to the anomalous and recently discovered crystal Hall effect, the topological Hall effect in noncoplanar antiferromagnets has been a subject of intensive research in the past decades. Here, we uncover a distinct flavor of the Hall effect emerging in generic canted spin systems. We demonstrate that upon canting, the anomalous Hall effect acquires a contribution which is sensitive to the sense of imprinted vector chirality among spins. We explore the origins and basic properties of corresponding chiral Hall effect, and closely tie it to the symmetry properties of the system. Our findings suggest that the chiral Hall effect and corresponding chiral magneto-optical effects emerge as useful tools in characterizing an interplay of structure and chirality in complex magnets, as well as in tracking their chiral dynamics and fluctuations.

Possible Topological Hall Effect above Room Temperature in Layered Cr1.2Te2 Ferromagnet.

Topological Hall effect (THE) has been used as a powerful tool to unlock spin chirality in novel magnetic materials. Recent focus has been widely paid to THE and possible chiral spin textures in two-dimensional (2D) layered magnetic materials. However, the room-temperature THE has been barely reported in 2D materials, which hinders its practical applications in 2D spintronics. In this paper, we report a possible THE signal featuring antisymmetric peaks in a wide temperature window up to 320 K in Cr1.2Te2, a new quasi-2D ferromagnetic material. The temperature, thickness, and magnetic field dependences of the THE lead to potential spin chirality origin that is associated with the spin canting under external magnetic fields. Our work holds promise for practical applications in future chiral spin-based vdW spintronic devices.

Magnetic structure and multiferroicity of Sc-substituted hexagonal YbFeO3

The hexagonal rare-earth ferrite $R\mathrm{Fe}{\mathrm{O}}_{3}$ family represents a unique class of multiferroics exhibiting weak ferromagnetism, and a strong coupling between magnetism and structural trimerization is predicted. However, the hexagonal structure for $R\mathrm{Fe}{\mathrm{O}}_{3}$ remains metastable in conventional conditions. We have succeeded in stabilizing the hexagonal structure of polycrystalline $\mathrm{Yb}\mathrm{Fe}{\mathrm{O}}_{3}$ by partial Sc substitution of Yb. Using bulk magnetometry and neutron diffraction, we find that ${\mathrm{Yb}}_{0.42}{\mathrm{Sc}}_{0.58}\mathrm{Fe}{\mathrm{O}}_{3}$ orders into a canted antiferromagnetic state with the N\'eel temperature ${T}_{N}\ensuremath{\sim}165\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, below which the ${\mathrm{Fe}}^{3+}$ moments form the triangular configuration in the $ab$ plane and their in-plane projections are parallel to the [100] axis, consistent with magnetic space group $P{6}_{3}{c}^{\ensuremath{'}}{m}^{\ensuremath{'}}$. It is determined that the spin canting is aligned along the $c$ axis, giving rise to the weak ferromagnetism. Furthermore, the ${\mathrm{Fe}}^{3+}$ moments reorient toward a new direction below reorientation temperature ${T}_{R}\ensuremath{\sim}40\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, satisfying magnetic subgroup $P{6}_{3}$, while the ${\mathrm{Yb}}^{3+}$ moments order independently and ferrimagnetically along the $c$ axis at the characteristic temperature ${T}_{\mathrm{Yb}}\ensuremath{\sim}15\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Interestingly, reproducible modulation of electric polarization induced by magnetic field at low temperature is achieved, suggesting that the delicate structural distortion associated with two-up/one-down buckling of the Yb/Sc planes and tilting of the $\mathrm{Fe}{\mathrm{O}}_{5}$ bipyramids may mediate the coupling between ferroelectric and magnetic orders under magnetic field. The present work represents substantial progress to search for high-temperature multiferroics in hexagonal ferrites and related materials.

Multiple Magnetic Phases in Van Der Waals Mn‐Doped SnS2 Semiconductor

Abstract2D van der Waals magnetic semiconductors have emerged along with the possibilities of achieving an efficient gate tunability and a proximity effect with a high magnetic anisotropy compared with 3D counterparts. Little explored are multiple magnetic phases with a single crystallographic phase. Herein, the multiple magnetic phases in a Mn‐doped SnS2 single crystal with different doping concentrations using a one‐step self‐flux method are reported. Two ferromagnetic phases with a canted spin direction exist regardless of the Mn‐doping concentration at up to 5 at%. Antiferromagnetism coexists with the ferromagnetic order and strengthens at high Mn‐doping concentrations. A magnetoresistance measurement conducted on a 2 at% Mn‐SnS2 flake exhibits a positive‐to‐negative crossover with a value of as high as 50% and clear anisotropy, confirming the presence of ferromagnetic order in the material. By revealing multiple magnetic phases in Mn‐doped SnS2, the study broadens the scope of state‐of‐the‐art research on layered magnetic semiconductors.

Microscopic understanding of particle-matrix interaction in magnetic hybrid materials by element-specific spectroscopy

Abstract Mössbauer spectroscopy is a well-known technique to study complex magnetic structures, due to its sensitivity to electronic and magnetic interactions of the probed nucleus with its electronic surrounding. It has also been applied to the emerging fields of magnetic hybrid materials as well as to ferrofluids, as information on the magnetic alignment and the velocity of the probed nucleus, i.e. of the particle it is embedded in, can be inferred from the spectra in addition to the above-mentioned quantities. Considering the wide range of preparation methods and sample properties, including fluids, particle powders, sintered pellets, polymer matrices and viscoelastic hydrogels, a considerable advantage of Mössbauer spectroscopy is the usage of γ-photons. This allows measurements on opaque samples, for which optical experiments are usually not feasible, also making the technique relatively independent of specific sample geometries or preparation. Using iron oxide nanoparticles in glycerol solution as an exemplary material here, the variety of system parameters simultaneously accessible via Mössbauer spectroscopy can be demonstrated: Spectra recorded for particles of different sizes provided information on the particles’ Brownian dynamics, including the effect of the shell thickness on their hydrodynamic diameter, the presence (or absence) and ballpark frequency of Néel superspin relaxation as well as the particles’ average magnetic orientation in external magnetic fields. For single-core particles, this resulted in the observation of standard Langevin-type alignment behavior. Mössbauer spectra additionally provide information on the absolute degree of spin alignment, also allowing the determination of the degree of surface spin canting, which limits the maximum magnetization of ferrofluid samples. Analyzing the alignment behavior of agglomerated particles for comparison, we found a completely different trend, in which spin alignment was further hindered by the competition of easy magnetic directions. More complex particle dynamics are observed when going from ferrofluids to hybrid materials, where the particle mobility and alignability depends not only on the particles’ shape and material, but also on the matrices’ inner structure and the acting force-transfer mechanism between particles and the surrounding medium. In ferrohydrogels for example, particle mobility in terms of Mössbauer spectroscopy was probed for different crosslinker concentrations, resulting in widely different mesh-sizes of the polymer network and different degrees of freedom. While a decrease in particle dynamics is clearly visible in Mössbauer spectroscopy upon rising crosslinker density, complementary AC-susceptometry experiments indicated no Brownian motion on the expected timescales. This apparent contradiction could, however, be explained by the different timescales of the experiments, probing either the relatively free Brownian motion on ultrashort timescales or the more bound state preventing extensive particle motion by interaction with the trapping mesh walls in the millisecond regime. However, it should also be considered that the effect of the surroundings on particle rotation in AC-susceptometry may also differ from the variation in translational motion, probed by Mössbauer spectroscopy. Being sensitive mainly to translational motion also results in a wide range of particles to be accessible for studies via Mössbauer spectroscopy, including larger agglomerates embedded in polymers, intended for remote-controlled heating. Despite the agglomerates’ wide distribution in effective diameters, information on particle motion was found to be in good agreement with AC-susceptometry experiments at ultralow frequencies in and above the polymer melting region, while additionally giving insight into Néel relaxation of the individual nanoparticles and their magnetic structure.

Low-dimensional magnetism of BaCuTe2O6

X-ray diffraction, thermodynamic measurements, and density-functional band-structure calculations are used to study the magnetic behavior of BaCuTe$_{2}$O$_{6}$, a member of the $A$CuTe$_2$O$_6$ structural family that hosts complex three-dimensional frustrated spin networks with possible spin-liquid physics. Temperature-dependent magnetic susceptibility and heat capacity of the Ba compound are well described by the one-dimensional spin-$\frac12$ Heisenberg chain model reminiscent of the Sr analog SrCuTe$_2$O$_6$. While the intrachain coupling $J/k_{\rm B}\simeq 37$ K is reduced compared to 49 K in the Sr compound, the N\'eel temperature increases from 5.5 K (Sr) to 6.1 K (Ba). Unlike the Sr compound, BaCuTe$_2$O$_6$ undergoes only one magnetic transition as a function of temperature and shows signatures of weak spin canting. We elucidate the microscopic difference between the Sr and Ba compounds and suggest that one of the interchain couplings changes sign as a result of negative pressure caused by the Sr/Ba substitution. The N\'eel temperature of BaCuTe$_2$O$_6$ is remarkably insensitive to the magnetic dilution with Zn$^{2+}$ up to the highest reachable level of about 20%.

Coexistence of Spin Canting and Metamagnetism in a One-Dimensional Mn(II) Compound Bridged by Alternating Double End-to-End and Double End-On Azido Ligands and the Analog Co(II) Compound

Two new compounds of general formula [M(N3)2(dmbpy)] in which dmbpy = 5,5′-dimethyl-2,2′-bipyridine, and M = Mn(II) or Co(II), have been solvothermally synthesized and characterized structurally and magnetically. The structures consist of zig-zag polymeric chains with alternating bis-µ(azide-N1)2M and bis-µ(azide-N1,N3)2M units in which the cis-octahedrally based coordination geometry is completed by the N,N’-chelating ligand dmbpy. The molecular structures are basically the same for each metal. The Mn(II) compound has a slightly different packing mode compared to the Co(II) compound, resulting from their different space groups. Interestingly, relatively weak interchain interactions are present in both compounds and this originates from π–π stacking between the dmbpy rings. The magnetic properties of both compounds have been investigated down to 2 K. The measurements indicate that the manganese compound shows spin-canted antiferromagnetic ordering with a Néel temperature of TN = 3.4 K and further, a field-induced magnetic transition of metamagnetism at temperatures below the TN. This finding affords the first example of an 1D Mn(II) compound with alternating double end-on (EO) and double end-to-end (EE) azido-bridged ligands, showing the coexistence of spin canting and metamagnetism. The cobalt compound shows a weak ferromagnetism resulting from a spin-canted antiferromagnetism and long-range magnetic ordering with a critical temperature, TC = 16.2 K.