Dc Magnetic Susceptibility Research Articles

Spin dynamics in ensembles of ultrafine ferrihydrite nanoparticles

Features of the spin dynamics in ensembles of interacting (FH-chem) and weakly interacting (FH-coated) magnetic ultrasmall ($\ensuremath{\langle}d\ensuremath{\rangle}\ensuremath{\sim}2$ nm) ferrihydrite nanoparticles have been explored. The dc and ac magnetic susceptibilities $[{\ensuremath{\chi}}^{\ensuremath{'}}(T)$ and ${\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}(T)]$ of the investigated samples have been thoroughly measured in a weak magnetic field (2 Oe) around the temperatures of superparamagnetic blocking of the nanoparticle magnetic moments (19 and 50.4 K for FH-coated and FH-chem, respectively, according to the dc magnetization data). It has been shown that the magnetic interactions between nanoparticles induce the formation of the cluster spin-glass state below the superparamagnetic blocking temperature (${T}_{g}=18$ and 49.5 K for FH-coated and FH-chem, respectively). It has been found that coating of nanoparticles increases the critical scaling index from $z\ensuremath{\nu}=5.9$ (FH-chem) to $z\ensuremath{\nu}=8.0$ (FH-coated). This indicates a general slowdown of the dynamics of correlated spins, which is also expressed as an increase in relaxation time ${\ensuremath{\tau}}_{0}$ after switching on the interparticle interactions. We attribute this phenomenon to a consequence of a change in the volume of correlated spins with the increasing size of a cluster of interacting nanoparticles. It has been demonstrated using the simulated ${\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}(T)$ dependence that the dissipation of the magnetic energy occurs in two independent stages. The first stage is directly related to the blocking of the nanoparticle magnetic moments, while the second stage reflects the spin-glass behavior of surface spins and depends strongly on the intensity of the interparticle interactions.

Magnetic Susceptibility of a Nanocomposite Based on an Opal Matrix with Yb2Ti2O7 Particles

The DC and AC magnetic susceptibilities of an opal matrix-based nanocomposite with pyrochlore-structured ytterbium titanate particles up to 60 nm in size have been studied in the range of magnetic fields up to 30 kOe. The measurements were performed at temperatures from 2 to 200 K. The temperature dependence of the nanocomposite Yb2Ti2O7 has been found to deviate significantly from the Curie–Weiss law. From the frequency dependence of the AC susceptibility measured in the range from 10 Hz to 10 kHz, the spin relaxation times have been determined, and two relaxation times have been found to be required for the description of the frequency dependence of the susceptibility. The field dependence of the AC susceptibility has been measured. This dependence is proved to be described by the modified Cole–Cole formula. The characteristic fields of the magnetic field dependence of the real part of the susceptibility are determined, the value of the characteristic field being found to increase with increasing temperatures.

Impact of organic amine cations on photoluminescence and magnetic properties in Dion-Jacobson hybrid manganese halide perovskites

A strenuous effort has been made to design multifunctional lead-free organic–inorganic hybrid (OIH) halide compounds, which are envisioned as next generation solar cell materials. However, it is challenging to design OIH halides that can exhibit both long-range magnetic ordering and high photoluminescence quantum yield (PLQY) since the dimensionality of the compounds has a contrasting effect on them. In this article, we have shown an approach to enhance PLQY in two-dimensional (2D) Heisenberg antiferromagnets by increasing the alkylene chain length of [H3N–(CH2)m–NH3]MnCl4 (m = 2, 3, and 4) compounds. All these compounds exhibit 2D layers of corner-sharing MnCl6 octahedra where the organic cations are intercalated between them. These compounds exhibit long-range antiferromagnetic ordering confirmed by the DC magnetic susceptibility and heat capacity measurements. The Néel temperature (TN) decreases with increasing the length of spacer cations due to a decrease in interlayer exchange interactions; however, interestingly, the lifetime of photoexcited electrons and PLQY enhances from 24 to 56 µs and 8% to 23%, respectively. Furthermore, the temperature-dependent photoluminescence measurements provide insight into thermal quenching and exciton binding energy. We believe this study can help to design new OIH halides with long-range magnetic ordering and high PLQY.

Effect of the Solvent on the Crystallographic and Magnetic Properties of Rhenium(IV) Complexes Based on 2,2′-Bipyrimidine Ligand

Two solvated rhenium(IV) complexes with formula [ReCl4(bpym)]·MeCN (1) and [ReCl4(bpym)]·CH3COOH·H2O (2) (bpym = 2,2′-bipyrimidine) have been prepared and characterized by means of Fourier transform infrared spectroscopy (FT–IR), scanning electron microscopy and energy dispersive X-ray analysis (SEM–EDX), single-crystal X-ray diffraction (XRD) and SQUID magnetometer. 1 and 2 crystallize in the monoclinic system with space groups P21/n and P21/c, respectively. In both compounds, the Re(IV) ion is six-coordinate and bound to four chloride ions and two nitrogen atoms of a 2,2′-bipyrimidine molecule forming a distorted octahedral geometry around the metal ion. In the crystal packing of 1 and 2, intermolecular halogen⋯halogen and π⋯halogen-type interactions are present. Hydrogen bonds take place only in the crystal structure of 2. Both compounds exhibit a similar crystal framework based on halogen bonds. Variable temperature dc magnetic susceptibility measurements performed on microcrystalline samples of 1 and 2 show a similar magnetic behavior for both compounds, with antiferromagnetic exchange between the Re(IV) ions connected mainly through intermolecular Re-Cl⋯Cl-Re interactions.

Magnetic ordering in Co2+-containing layered double hydroxides via the low-temperature heat capacity and magnetisation study

The low-temperature heat capacity and the magnetisation of Co2+nAl3+ layered double hydroxides (LDH) with the cobalt-to-aluminium ratio n = 2 and 3 and intercalated with different anions have been studied in a wide range of magnetic fields up to 50 kOe. The heat capacity, C(T), was found to demonstrate a Schottky-like anomaly observed as a broad local maximum in the temperature dependence below 10 K. The effect is caused by a splitting of the ground-state Kramers doublet of Co2+ in the internal exchange field and correlates with magnetic ordering in these LDH. In low applied fields, the temperature-dependent dc magnetic susceptibility demonstrates a pronounced rise, which is associated with an onset of magnetic ordering. Both the heat capacity anomaly and the magnetic susceptibility peak are more pronounced for the LDH with n = 2 than for those with n = 3. This feature is associated with an excess of the honeycomb-like CoAl coordination (which corresponds to a 2:1 CoAl ordering) over the statistical cation distribution in Co2Al LDH, while a rather random cobalt-aluminium distribution is typical for Co3Al LDH. The temperature of the Schottky-like anomaly measured in a zero field is independent of the interlayer distance. Application of the magnetic field results in a widening of the anomaly range and a shift to higher temperatures. The observed experimental data are typical for a cluster spin glass ground state.

3d Ion-Driven Hexanuclear Heterometallic Clusters with Amazing Structures and Magnetic Properties

By using a heptadentate Schiff base ligand with three NO2 pockets to react with 3d and 4f acetate precursors, three series of M4Ln2 complexes (M, Ln = Ni, Gd for 1NiGd; Ni, Dy for 2NiDy; Co, Gd for 3CoGd; Co, Dy for 4CoDy; Cu, Gd for 5CuGd; Cu, Dy for 6CuDy) have been obtained and characterized. X-ray single-crystal diffraction analyses indicated that Ni4Ln2 series exhibit butterfly structures with extended wings, the Co4Ln2 series are made up of four fused linear defective open cubes, and the Cu4Ln2 series display H-typed topology structures. The dc magnetic susceptibility data revealed that all of the Gd derivatives possess significant magnetic entropy change, whereas the alternating current (ac) magnetic susceptibility measurements identified that only the NiDy derivative displays single-molecule magnet behavior with energy barrier of 15.69 K under zero dc field. These results reveal that 3d ions are important in adjusting the structure and magnetic properties for 3d–4f complexes.

A cascade of magnetic phase transitions and a 1/3-magnetization plateau in selenite-selenate Co3(SeO3)(SeO4)(OH)2 with kagomé-like Co2+ ion layer arrangements: the importance of identifying a correct spin lattice.

We prepared a new compound, Co3(SeO3)(SeO4)(OH)2, having layers in a kagomé-like arrangement of Co2+ (spin S = 3/2) ions. This phase crystallizes in the orthorhombic space group Pnma (62) with unit cell parameters a = 11.225(9) Å, b = 6.466(7) Å and c = 11.530(20) Å. Its layers, parallel to the ab-plane, are made up of Co1O5 square pyramids and Co2O6 and Co3O6 octahedra. As the temperature is lowered, Co3(SeO3)(SeO4)(OH)2 undergoes three successive magnetic transitions at 27.5, 19.4 and 8.1 K, and the magnetization of Co3(SeO3)(SeO4)(OH)2 measured at 2.4 K exhibits a 1/3-magnetization plateau between 7.8 and 19.9 T. TheH-Tmagnetic phase diagram constructed for Co3(SeO3)(SeO4)(OH)2from ac and dc magnetic susceptibility, specific heat and magnetization measurements contains three magnetic phases I, II and III. Phase I is antiferromagnetic, while phases II and III are ferrimagnetic and responsible for the 1/3-magnetization plateau. To interpret these complex magnetic properties, we identified the correct spin lattice for Co3(SeO3)(SeO4)(OH)2 by evaluating its intralayer and interlayer spin exchanges based on spin-polarized DFT+U calculations.

Synthesis, structure, and characterisation of a ferromagnetically coupled dinuclear complex containing Co(II) ions in a high spin configuration and thiodiacetate and phenanthroline as ligands and of a series of isomorphous heterodinuclear complexes containing different Co : Zn ratios.

We report the synthesis, crystal structure, and characterisation of a dinuclear Co(II) compound with thiodiacetate (tda) and phenanthroline (phen) as ligands (1), and of a series of metal complexes isomorphous to 1 with different Co : Zn ratios (2, 4 : 1; 3, 1 : 1; 4, 1 : 4; 5, 1 : 10). General characterisation methodologies and X-ray data showed that all the synthesised complexes are isomorphous to Zn(II) and Cu(II) analogues (CSD codes: DUHXEL and BEBQII). 1 consists of centrosymmetric Co(II) ion dimers in which the ions are 3.214 Å apart, linked by two μ-O bridges. Each cobalt atom is in a distorted octahedral environment of the N2O3S type. UV-vis spectra of 1 and 5 are in line with high spin (S = 3/2) Co(II) ions in octahedral coordination and indicate that the electronic structure of both Co(II) ions in the dinuclear unit does not significantly change relative to that of the magnetically isolated Co(II) ion. EPR spectra of powder samples of 5 (Co : Zn ratio of 1 : 10) together with spectral simulation indicated high spin Co(II) ions with high rhombic distortion of the zfs [E/D = 0.31(1), D > 0]. DC magnetic susceptibility experiments on 1 and analysis of the data constraining the E/D value obtained by EPR yielded g = 2.595(7), |D| = 61(1) cm-1, and an intradimer ferromagnetic exchange coupling of J = 1.39(4) cm-1. EPR spectra as a function of Co : Zn ratio for both powder and single crystal samples confirmed that they result from two effective S' = 1/2 spins that interact through dipolar and isotropic exchange interactions to yield magnetically isolated S' = 1 centres and that interdimeric exchange interactions, putatively mediated by hydrophobic interactions between phen moieties, are negligible. The latter observation contrasts with that observed in the Cu(II) analogue, where a transition from S = 1 to S' = 1/2 was observed. Computational calculations indicated that the absence of the interdimeric exchange interaction in 1 is due to a lower Co(II) ion spin density delocalisation towards the metal ligands.

Exploiting Strong {CrIII–DyIII} Ferromagnetic Exchange Coupling to Quench Quantum Tunneling of Magnetization in a Novel {CrIII2DyIII3} Single-Molecule Magnet

The {3d–4f} pentanuclear complexes with the formula [CrIII2LnIII3(PhCO2)7(OH)6 (iPrO)(NO3)(H2O)3] (iPrO = isopropoxide) (where Ln = Dy (1), Gd (2)) have been synthesized and characterized using magnetic and theoretical studies. The metal core of complexes 1 and 2 has a trigonal bipyramidal arrangement with three LnIII ions in the triangular plane and two CrIII ions occupying the axial positions. These ions are held together by six μ3-OH bridges and seven carboxylate bridges. The dc magnetic susceptibility data reveal ferromagnetic interactions presiding between CrIII and LnIII ions in 1 and 2. The fitting of the susceptibility curve employing the DFT calculated J (vide infra), yield JGdIII–GdIII = +0.008 cm–1, JCrIII–GdIII = +0.27 cm–1, and JCrIII–CrIII = −0.007 cm–1 for 2. The dynamic (ac) magnetic susceptibility studies on 1 indicate slow relaxation of magnetization with a Ueff value of 30.9 K (21.4 cm–1) and τ0 = 4.09 × 10–10 s. These extracted parameters are among the highest for any reported {CrIIIDyIII} complexes. DFT and ab initio CASSCF/RASSI–SO/SINGLE_ANISO/POLY_ANISO calculations were carried out to estimate the exchange interactions and their role in quenching the quantum tunneling of magnetization (QTM) behavior. Ab initio calculations on the DyIII ions reveal three asymmetric DyIII centers with the estimated single ion barrier in the range of 78–184 cm–1, however, with a large QTM probability. Despite a triangular {Dy3} motif, the gzz axes do not align in the triangular plane as observed in the {CrIIIDyIII6} single-molecule toroids (SMT) reported earlier by us. This is essentially due to the presence/absence of the iPrO–/carboxylate group that alters the charge distribution around the DyIII ion and hence the orientation of the corresponding gzz axis. The combination of DFT and ab initio CASSCF calculations yield JDyIII–DyIII = +0.012 cm–1, JCrIII–DyIII = +1.20 cm–1, and JCrIII–CrIII = −0.95 cm–1 for 1. The mechanism of magnetization relaxation developed for the {CrIII2DyIII3} cluster reveals that the relatively strong ferromagnetic CrIII–DyIII exchange interaction reduces the ground state QTM significantly yielding a Ueff of 38.6 cm–1, which agrees with the experimental value. Thus, our study iterates the importance of CrIII ion to enhance the exchange coupling in the {3d–4f} family of clusters.

Preparation, characterization and magnetic properties of Sm0.95Ho0.05FeO3 nanoparticles and their application in the purification of water

Sm0.95Ho0.05FeO3 was successfully prepared in a single phase using the citrate combustion method. The investigated sample was characterized using X-ray diffraction (XRD), a high-resolution transmission electron microscope (HRTEM) and X-ray photoemission spectroscopy (XPS). XRD confirmed that the sample was synthesized in an orthorhombic phase with an average crystallite size of 12 nm. HRTEM indicated that the sample was prepared in the nanoscale with an average particle size of 18 nm. XPS was used to identify the chemical bonds, binding energies and core levels of Sm0.95Ho0.05FeO3. The magnetic properties were studied using a vibrating sample magnetometer and DC magnetic susceptibility using Faraday’s method. The sample has an antiferromagnetic behavior with weak ferromagnetic components. The presence of magnetic Ho3+ ions in the SmFeO3 sample causes the magnetic exchange interaction between the 2p orbital of Fe3+ and the 4d sub-shell of Ho3+ ions. The dependence of pH value on the removal efficiency of Pb2+ from water was studied. The maximum Pb2+ removal efficiency of the Ho-doped SmFeO3 nano perovskite is 26% at pH = 5 and 99% at pH = 8. The Freundlich, Langmuir and Temkin isotherms were studied to understand the adsorption mechanism. The Temkin adsorption isotherm best fitted with the experimental data.

Lanthanide metal-organic frameworks containing ferromagnetically coupled metal-carboxylate chains showing slow magnetic relaxation behavior

Lanthanide metal-organic frameworks (Ln-MOFs) with slow magnetic relaxation behavior are of great interest to scientists due to their rich and peculiar physical phenomena and spin-related applications. In this contribution, the syntheses, characterizations and magnetic properties of two new Ln-MOFs: {[Ln2(btpdc)3·DMF·2H2O]·2DMF·4H2O}n (Ln = Dy (1), Gd (2), H2btpdc = benzo[b]thiophene-2,6-dicarboxylic acid) are reported. Single crystal X-ray diffraction experiments show the two complexes are isostructural with three dimensional (3D) porous framework structure constructed by metal-carboxylate chains separated by long organic linkers. Direct-current (dc) magnetic susceptibilities recorded under 1000 Oe reveal the overall exchange couplings in both the two MOFs are ferromagnetic. Interestingly, the ferromagnetic coupled metal-carboxylate chains in 1 are sufficiently isolated by the long organic linkers that makes 1 exhibit slow magnetic relaxation behavior and Ising-like behavior which was rarely reported for lanthanide-carboxylate complexes.

Static and Resonant Properties and Magnetic Phase Diagram of LiMn2TeO6.

Physical properties of the mixed-valent tellurate of lithium and manganese, LiMn2TeO6, were investigated in measurements of ac and dc magnetic susceptibility χ, magnetization M, specific heat Cp, electron spin resonance (ESR), and nuclear magnetic resonance (NMR) in the temperature range 2−300 K under magnetic field up to 9 T. The title compound orders magnetically in two steps at T1 = 20 K and T2 = 13 K. The intermediate phase at T2 < T < T1 is fully suppressed by magnetic field µ0H of about 4 T. Besides magnetic phases transitions firmly established in static measurements, relaxation-type phenomena were observed well above magnetic ordering temperature in resonant measurements.

Discovery of superconductivity in K-doped 2,2[formula omitted]-bipyridine

Organic compounds are always promising candidates of superconductors with high transition temperatures. The 2,2′-bipyridine solely composed by C, H, and N atoms is examined for this proposal. The presence of Meissner effect with a transition temperature of 7.2 K in this material upon potassium doping is demonstrated by the dc magnetic susceptibility measurements. The real part of the ac susceptibility exhibits the same transition temperature as that in dc magnetization, and a sharp peak appeared in the imaginary part indicates the formation of the weakly linked superconducting vortex current. The occurrence of superconductivity is further supported by the resistance drop at the transition together with its suppression by the applied magnetic fields. The superconducting phase is identified to be K3-2,2′-bipyridine with P21 space-group from the analysis of Raman scattering spectra and X-ray diffraction patterns as well as the first-principles calculations. This work not only opens an encouraging window for finding superconductivity after optoelectronics in 2,2′-bipyridine-based materials but also offers an example to realize superconductivity from conducting polymers and their derivatives.

Dielectric and Spin-Glass Magnetic Properties of the A-Site Columnar-Ordered Quadruple Perovskite Sm2CuMn(MnTi3)O12

Perovskite-type ABO3 oxides show a number of cation-ordered structures, which have significant effects on their properties. The rock-salt-type order is dominant for B cations, and the layered order for A cations. In this work, we prepared a new perovskite-type oxide, Sm2CuMn(MnTi3)O12, with a rare columnar A-site order using a high-pressure, high-temperature method at about 6 GPa and about 1700 K. Its crystal structure was studied with synchrotron powder X-ray diffraction. The compound crystallizes in space group P42/nmc (No. 137) at room temperature with a = 7.53477 Å and c = 7.69788 Å. The magnetic properties of the compound were studied with dc and ac magnetic susceptibility measurements and specific heat. Spin-glass (SG) magnetic properties were found with TSG = 7 K, while specific heat, in the form of Cp/T, showed a strong, very broad anomaly developing below 20 K and peaking at 4 K. The dielectric constant of Sm2CuMn(MnTi3)O12 was nearly frequency and temperature independent between 8 K and 200 K, with a value of about 50. Cu2+ doping drastically modified the magnetic and dielectric properties of Sm2CuMn(MnTi3)O12 in comparison with the parent compound Sm2MnMn(MnTi3)O12, which showed a long-range ferrimagnetic order at 34-40 K. The antisite disorder of Cu2+ and Mn2+ cations between square-planar and octahedral sites was responsible for the SG magnetic properties of Sm2CuMn(MnTi3)O12.

Structural, morphological and magnetic properties of hexaferrite BaCo2Fe16O27 nanoparticles and their efficient lead removal from water

W-hexaferrite BaCo2Fe16O27 was prepared using the citrate nitrate combustion method. The sample was characterized using XRD, SEM, EDX and elemental mapping. XRD confirmed that the sample was synthesized in a single phase hexagonal structure with an average crystallite size 37.39 nm. SEM images of the sample show a spongy morphology with the agglomerated grain owing to dipole interaction between the crystallites. The magnetic properties of BaCo2Fe16O27 were studied using H-M hysteresis loop and the DC magnetic susceptibility. The sample has a ferrimagnetic behavior with saturation magnetization 64.133 emu/g. The magnetic properties of BaCo2Fe16O27 are originated from the Fe3+–O–Fe3+ superexchange. The synthesized sample is used as an adsorbent to remove the heavy metal Pb2+ from water. BaCo2Fe16O27 has Pb2+ removal efficiency 99% and 28% at pH 8 and 7 respectively. The Langmuir and Freundlich isotherms were used to analyze the experimental data. The Freundlich adsorption isotherm fitted the experimental data well.

Pinning potential in highly performant CaKFe4As4 superconductor from DC magnetic relaxation and AC multi-frequency susceptibility studies

We have investigated the pinning potential of high-quality single crystals of superconducting material CaKFe4As4 having high critical current density and very high upper critical field using both magnetization relaxation measurements and frequency-dependent AC susceptibility. Preliminary studies of the superconducting transition and of the isothermal magnetization loops confirmed the high quality of the samples, while temperature dependence of the AC susceptibility in high magnetic fields show absolutely no dependence on the cooling conditions, hence, no magnetic history. From magnetization relaxation measurements were extracted the values of the normalized pinning potential U*, which reveals a clear crossover between elastic creep and plastic creep. The extremely high values of U*, up to 1200 K around the temperature of 20 K lead to a nearly zero value of the probability of thermally-activated flux jumps at temperatures of interest for high-field applications. The values of the creep exponents in the two creep regimes resulted from the analysis of the magnetization relaxation data are in complete agreement with theoretical models. Pinning potentials were also estimated, near the critical temperature, from AC susceptibility measurements, their values being close to those resulted (at the same temperature and DC field) from the magnetization relaxation data.

Magnetic incommensurability, short-range correlations, and properties ofHo7Rh3

The crystal structure, thermal properties, and magnetic state of the rare-earth intermetallic compound ${\mathrm{Ho}}_{7}{\mathrm{Rh}}_{3}$ was studied using the measurements of the AC and DC magnetic susceptibility, magnetization, specific heat and thermal expansion, as well as by neutron and synchrotron powder diffraction. Below the N\'eel temperature ${T}_{\mathrm{N}}=32$ K, an incommensurate antiferromagnetic (AFM) structure of the spin density wave (SDW) type was observed, described by the magnetic superspace group $Cmc{2}_{1.}{1}^{\ensuremath{'}}(00g)0sss$ and the propagation vector ${\mathbf{k}}_{\mathrm{IC}}=(0\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}0.389)$. Further cooling leads to the spin reorientation transition and squaring-up transformation of the SDW magnetic structure below ${T}_{t1}=22$ K. The spin reorientation transition is accompanied by the emergence of a ferromagnetic component in the incommensurate magnetic structure upon cooling below ${T}_{t2}=9$ K. Using neutron diffraction, the existence of a short-range antiferromagnetic order was revealed up to temperatures twice as high as ${T}_{\mathrm{N}}$. These short-range AFM correlations were found to affect the magnetic susceptibility and thermal expansion, while the crystal structure retains its hexagonal symmetry below and above the N\'eel temperature.

Muon Spin Relaxation Study of Frustrated Tm3Sb3Mg2O14 with Kagomé Lattice

The structure and magnetic properties of rare-earth ions Tm3+ Kagomé lattice Tm3Sb3Mg2O14 are studied by x-ray diffraction, magnetic susceptibility and muon spin relaxation (μSR) experiments. The existence of a small amount of Tm/Mg site-mixing disorder is revealed. DC magnetic susceptibility measurement shows that Tm3+ magnetic moments are antiferromagnetically correlated with a negative Curie–Weiss temperature of –26.3 K. Neither long-range magnetic order nor spin-glass transition is observed by DC and AC magnetic susceptibility, and confirmed by μSR experiment down to 0.1 K. However, the emergence of short-range magnetic order is indicated by the zero-field μSR experiments, and the absence of spin dynamics at low temperatures is evidenced by the longitudinal-field μSR technique. Compared with the results of Tm3Sb3Zn2O14, another Tm-based Kagomé lattice with much more site-mixing disorder, the gapless spin liquid like behaviors in Tm3Sb3Zn2O14 can be induced by disorder effect. Samples with perfect geometrical frustration are in urgent demand to establish whether QSL exists in this kind of materials with rare-earth Kagomé lattice.

Low-temperature magnetic order rearrangement in the layered van der Waals compound MnPS3

To stabilize the long-range magnetic ordering in two-dimensional (2D) materials is a challenge from both fundamental and application points of view. It is difficult to be realized due to the delicate competition between thermal energy, magnetic exchange energy, and spin frustration. Here we study the temperature and field effects on the spin structure of two-dimensional van der Waals system ${\mathrm{MnPS}}_{3}$ using dc magnetic susceptibility and electron spin resonance (ESR) techniques. Clear development of three-step transitions was observed in the in-plane susceptibility. A low-temperature plateau from 78 to 38 K can be related to the Heisenberg antiferromagnetic (HAFM) ordering with spins pointing to the $z$ direction. Following, a sharp rising after the plateau suggests a transition into the $XY$ system. The rising slope slows down at 30 K indicating a transition into another phase, possibly a vortex-antivortex state. By fitting the temperature-dependent ESR parameters with the Berezinskii-Kosterlitz-Thouless (BKT) model in the range 100--300 K, we propose a spin 2D system with the vortex-antivortex structure below the HAFM transition. Susceptibility and ESR data show that the application of a high field along the $z$ direction destroys both the $XY$ phase and the BKT transition, reconciling to the scenario of a topological phase transition at zero field.

Observation of field-induced single-molecule magnet behavior in an octahedrally coordinated binuclear Co2 compound

A binuclear cobalt compound, namely, [Co2(L)2Cl2(H2O)4]·2Cl·2H2O (1), was synthesized by acylhydrazone Schiff base ligand N3-(4-pyridyl)-4-hydroxybenzoylhydrazone (HL) and CoCl2·6H2O. The crystal structure study suggests that each CoII ion in 1 is surrounded by two nitrogen atoms and one oxygen atom from ligand, one chloride ion and two oxygen atoms from two water molecules, giving rise to six-coordinated geometry, where two N atoms from two ligands as bridges link two CoII ions. The direct-current (dc) magnetic susceptibility measurements reveal the existence of antiferromagnetic coupling interaction in 1. The alternating-current (ac) magnetic susceptibility measurements indicate that 1 exhibits field-induced slow magnetic relaxation behavior with energy barrier (Ueff) of 51.80 K, standing out among Co2-SMMs. This study demonstrates that the large magnetic anisotropy of each CoII ion and the weak antiferromagnetic coupling interaction between two CoII ions can improve Co2-SMMs performance effectively.