Dc Susceptibility Research Articles

Spin-glass behavior in Li3NiCuBiO6: a two-dimensional distorted honeycomb-lattice

We report a detailed experimental study on the structural and magnetic properties of Li3NiCuBiO6 by means of various characterization techniques. It crystallizes into a monoclinic crystal structure composed of a layered magnetic honeycomb lattice along the c-axis. The existence of glassy state below 4 K is indicated by dc and ac susceptibility measurements. Magnetic contribution to the total heat capacity also peaks around the freezing temperature, and its linear temperature dependence backs our claim of a glassy state in the compound. The calculated magnetic entropy unveils that only ∼26% of the total entropy is released for the system (), and a tremendous amount of spin entropy is still retained in the system. Further, analysis of the frequency-dependent freezing temperature with the help of power law confirms the presence of a spin glass state. Moreover, the appearance of magnetic memory and relaxation effect below freezing temperature manifest the development of the system via a large number of intermediate metastable states. All these measurements confirm the spin-glass behavior of the compound. We consider the presence of different magnetic atoms in honeycomb lattice as the main driving factor for the spin-glass ground state.

Spin-ice behavior of mixed pyrochlore Dy2GaSbO7 exhibiting enhanced Pauling zero-point entropy

Herein, the low-temperature magnetothermal properties and spin-ice physics of a mixed pyrochlore, Dy2GaSbO7 (DGS), are investigated through dc magnetization, ac susceptibility, and heat capacity experiments, and crystal-field computation. A Curie-Weiss (CW) fit to the dc susceptibility data yields effective magnetic moment, μeff = 10.0 μB/Dy3+ and CW temperature, θCW = +1.62 K. Magnetization attains a saturation value of Msat = 5.06μB/Dy above H ≈ 8 T and at T = 2 K, which is half of the μeff due to the effective Ising-type anisotropy along local 〈111〉 axes of the elementary Dy4O′ tetrahedron, illustrating DGS as an effective spinS∼ = 1/2 system. The dc susceptibility data are interpreted satisfactorily within the framework of a crystal-field theory and a mean-field approximation taking account of long-range dipolar interactions and anisotropic exchange interactions between the nearest-neighbor Dy3+-ions. AC susceptibility exhibits anomaly at a temperature Tice ≈ 3.13 K at frequency of f = 111 Hz, which is a signature of dynamical freezing of spins into a disordered state in compliance with the spin-ice rules. Heat capacity at zero field also shows a peak at 1.36 K and a low kink at 3.25 K which smears out on application of the magnetic field. The calculated magnetic entropy of DGS at zero field is 2.82 J K−1(mol-Dy)−1, which is much less than the Pauling spin-ice value of 4.1 J K−1mol−1. The spin-ice entropy is restored with a value of 4.50 J K−1(mol-Dy)−1 at a field of 1 T. The zero-point entropy of DGS becomes 2.94 J K−1(mol-Dy)−1 which is larger than Pauling zero-point entropy of 1.686 J K−1mol−1 for cannonical dipolar spin-ice materials, e.g., Dy2Ti2O7 and Ho2Ti2O7. The enhanced entropy of DGS may be induced due to random chemical disorder and varied chemical pressure of B-site (GaSb tetrahedra) ions. Thus, the present study creates a new pathway to extend the horizon of spin-ice physics.

Anomalous Ferromagnetic Behavior in Orthorhombic Li3Co2SbO6.

Monoclinic Li3Co2SbO6 has been proposed as a Kitaev spin liquid candidate and investigated intensively, whereas the properties of its polymorph, the orthorhombic phase, are less known. Here we report the magnetic properties of orthorhombic Li3Co2SbO6 as revealed by dc and ac magnetic susceptibility, muon spin relaxation (μSR), and neutron diffraction measurements. Successive magnetic transitions at 115, 89, and 71 K were observed in the low-field dc susceptibility measurements. The transitions below TN (115 K) are suppressed at higher applied fields. However, zero-field ac susceptibility measurements reveal distinct frequency-independent transitions at about 114, 107, 97, 79, and 71 K. A long-range magnetic ordered state was confirmed by specific heat, μSR, and neutron diffraction measurements, all indicating a single transition at about 115 K. The discrepancy between different measurements is attributed to possible stacking faults and/or local disorders of the ferromagnetic zigzag chains, resulting in ferromagnetic boundaries within the overall antiferromagnetic matrix.

Unravelling the signatures of effective spin moments in CeVO4: magnetization and heat capacity study

The realization of an effective spin (Jeff ) ½ state at low temperatures offers a platform to study the enthralling physics behind the disordered states in certain systems. Here, we report the signatures of magnetic ground state associated with Jeff = ½ in CeVO4. Our studies confirm the absence of any ordering or freezing down to 1.8 K. In the low temperature region, the Curie–Weiss fit of the inverse DC susceptibility indicate towards the presence of antiferromagnetic correlations among the Ce3+ spins. The calculated value of effective moment (∼1.16 ) corresponds to J = ½ with gJ ∼ 1.20. Further, the field dependent magnetization curve at 2 K follows a behaviour corresponding to J= ½ Brillouin function with gJ ∼ 1.13. Magnetic field dependent heat capacity fits very well with two-level Schottky scheme. Our investigations suggest that CeVO4 can be a promising candidate to realise Jeff = ½ properties among 3D spin systems.

A Tetranuclear Dysprosium Schiff Base Complex Showing Slow Relaxation of Magnetization

A tetranuclear dysprosium Schiff base complex was isolated by reacting dysprosium chloride with 2-hydroxy-3-methoxybenzaldehyde and 2-(aminomethyl)pyridine in-situ under basic conditions. The isolated Dy(III) complex was characterized by elemental analyses, single crystal X-ray diffraction and molecular spectroscopy. The complex crystallizes in the triclinic space group P-1 with unit cell parameters of a = 10.2003 (4), b = 13.8602 (5), c = 14.9542 (6), α = 94.523 (3), β = 109.362 (4), and γ = 99.861 (3). The magnetic properties of 1 have been investigated by DC and AC susceptibility measurements. The DC measurements reveal weak exchange coupling of antiferromagnetic nature. In the AC measurement, the complex shows a slow relaxation of magnetization in the absence of an external magnetic field.

A Smart Molecule Showing Spin Crossover Responsive Aggregation-Induced Emission

A Smart Molecule Showing Spin Crossover Responsive Aggregation-Induced Emission

Antiferromagnetic short-range order and cluster spin-glass state in diluted spinel ZnTiCoO4

The nature of magnetism in the doubly-diluted spinel ZnTiCoO4 = (Zn2+) A [Ti4+Co2+] B O4 is reported here employing the temperature and magnetic field (H) dependence of dc susceptibility (χ), ac susceptibilities (χ′ and χ″), and heat capacity (C p) measurements. Whereas antiferromagnetic (AFM) Néel temperature T N = 13.9 K is determined from the peak in the ∂(χT)/∂T vs T plot, the fit of the relaxation time τ (determined from the peak in the χ″ vs T data at different frequencies) to the Power law: τ = τ 0 [(T − T SG)/T SG]−zν yields the spin glass freezing temperature T SG = 12.9 K, z ν ∼ 11.75, and τ 0 ∼ 10−12 s. Since the magnitudes of τ 0 and z ν depend on the magnitude of T SG, a procedure is developed to find the optimum value of T SG = 12.9 K. A similar procedure is used to determine the optimum T 0 = 10.9 K in the Vogel–Fulcher law: τ = τ 0 exp[E a/k B(T − T 0)] yielding E a/k B = 95 K, and τ 0 = 1.6 × 10−13 s. It is argued that the comparatively large magnitude of the Mydosh parameter Ω = 0.026 and k B T 0/E a = 0.115 (≪1) suggests cluster spin-glass state in ZnTiCoO4 below TSG. In the C p vs T data from 1.9 K to 50 K, only a broad peak near 20 K is observed. This and absence of λ-type anomaly near T N or T SG combined with the reduced value of change in magnetic entropy from 50 K to 1.9 K suggests only short-range AFM ordering in the system, consistent with spin-glass state. The field dependence of T SG shows slight departure (ϕ ∼ 4.0) from the non-mean-field Almeida–Thouless line T SG(H) = T SG(0) (1 − AH 2/ϕ ). Strong temperature dependence of magnetic viscosity S and coercivity H C without exchange bias, both tending to zero on approach to T SG from below, further support the spin-glass state which results from magnetic dilution driven by diamagnetic Zn2+ and Ti4+ ions leading to magnetic frustration. Magnetic phase diagram in the H–T plane is established using the high-field magnetization data M(H, T) for T < T N which reveals rapid decrease of T SG with increase in H whereas decrease in T N with increase in H is weaker, typical of AFM systems. For T > T N, the data of χ vs T are fit to the modified Curie–Weiss law, χ = χ 0 + C/(T + θ), with χ 0 = 3.2 × 10−4 emu mol−1 Oe−1 yielding θ = 4 K and C = 2.70 emu K mol−1 Oe−1. This magnitude of C yields effective magnetic moment = 4.65 μ B for Co2+, characteristic of Co2+ ions with some contribution from spin–orbit coupling. Molecular field theory with effective spin S = 3/2 of Co2+ is used to determine the nearest-neighbor exchange constant J 1/k B = 2.39 K AFM and next-nearest-neighbor exchange constant J 2/k B = −0.66 K (ferromagnetic).

Structure and magnetic studies of geometrically frustrated disordered pyrochlores A2Zr2O7: (A [formula omitted] Eu, Gd, Er)

Dy2Ti2O7 and Ho2Ti2O7 are the well-known spin ice systems where the replacement of Ti with Zr destabilizes the pyrochlore lattice and leads to the dynamic ground state. We have studied a series of disordered pyrochlore oxides A2Zr2O7 (A = Eu, Gd, Er) and compared their crystal structure, magnetic, and heat capacity behavior with that of Dy2Zr2O7 and Ho2Zr2O7 systems. The analysis of the dc susceptibility curves suggests these systems as a frustrated antiferromagnet with negative Curie–Weiss temperature. Eu2Zr2O7 exhibited a temperature-independent dc susceptibility in the range T = 20–90 K, which persist even at high fields due to the Van Vleck contribution. Gd2Zr2O7 and Er2Zr2O7 shows an unusual field-induced spin freezing anomaly near T≈ 10 K which is similar to (Dy/Ho)2Zr2O7 systems. These studies show that depending on the disorder parameter, the spin-freezing behavior can be induced by slowing down the spin dynamic with a suitable choice of the magnetic field. We observed that, unlike titanates, modification at the rare-earth site does not make a considerable change in the magnetic ground state of these Dy, Ho, Er, Gd based zirconates compounds.

Non-magnetic ion site disorder effects on the quantum magnetism of a spin-1/2 equilateral triangular lattice antiferromagnet

With the motivation to study how non-magnetic ion site disorder affects the quantum magnetism of Ba3CoSb2O9, a spin-1/2 equilateral triangular lattice antiferromagnet, we performed DC and AC susceptibility, specific heat, elastic and inelastic neutron scattering measurements on single crystalline samples of Ba2.87Sr0.13CoSb2O9 with Sr doping on non-magnetic Ba2+ ion sites. The results show that Ba2.87Sr0.13CoSb2O9 exhibits (i) a two-step magnetic transition at 2.7 K and 3.3 K, respectively; (ii) a possible canted 120 degree spin structure at zero field with reduced ordered moment as 1.24 μ B/Co; (iii) a series of spin state transitions for both H∥ab-plane and H∥c-axis. For H∥ab-plane, the magnetization plateau feature related to the up–up–down phase is significantly suppressed; (iv) an inelastic neutron scattering spectrum with only one gapped mode at zero field, which splits to one gapless and one gapped mode at 9 T. All these features are distinctly different from those observed for the parent compound Ba3CoSb2O9, which demonstrates that the non-magnetic ion site disorder (the Sr doping) plays a complex role on the magnetic properties beyond the conventionally expected randomization of the exchange interactions. We propose the additional effects including the enhancement of quantum spin fluctuations and introduction of a possible spatial anisotropy through the local structural distortions.

Comparative study of the structural and magnetic properties of Mn1/3NbS2 and Cr1/3NbS2

We compare the magnetism of single crystals of the intercalated transition metal dichalcogenides ${\mathrm{Cr}}_{1/3}\mathrm{Nb}{\mathrm{S}}_{2}$ and ${\mathrm{Mn}}_{1/3}\mathrm{Nb}{\mathrm{S}}_{2}$ using techniques such as dc and ac susceptibility and Lorentz transmission electron microscopy (LTEM). We present a detailed structural investigation of these materials using electron and single-crystal x-ray diffraction measurements to show how substitutional disorder and stacking faults can manifest in ${\mathrm{Cr}}_{1/3}\mathrm{Nb}{\mathrm{S}}_{2}$ and ${\mathrm{Mn}}_{1/3}\mathrm{Nb}{\mathrm{S}}_{2}$, and give rise to additional superlattice reflections in diffraction patterns acquired from ${\mathrm{Mn}}_{1/3}\mathrm{Nb}{\mathrm{S}}_{2}$. Magnetic susceptibility and LTEM measurements show ${\mathrm{Cr}}_{1/3}\mathrm{Nb}{\mathrm{S}}_{2}$ displays chiral helimagnetism below its magnetic ordering temperature (${T}_{\mathrm{C}}$) of 111 K, while there is no evidence that ${\mathrm{Mn}}_{1/3}\mathrm{Nb}{\mathrm{S}}_{2}$ exhibits helimagnetic ordering below its transition temperature ${T}_{\mathrm{C}}=45$ K.

On the magnetic structure and magnetic behaviour of the most distorted member of the series of RNiO3 perovskites (R = Lu).

The crystal structure of LuNiO3 perovskite has been examined below RT and across TN = 125 K by neutron powder diffraction. In this temperature region (2-298 K), well below the metal-insulator transition this oxide exhibits at TMI = 599 K, this material is insulating and characterized by a partial charge disproportionation of the Ni valence. In the perovskite structure, defined in the monoclinic P21/n space group, there are two inequivalent Ni sites located in alternating octahedra of different sizes. The structural analysis with high-resolution techniques (λ = 1.594 Å) unveils a subtle increase of the charge disproportionation as temperature decreases, reaching δeff = 0.34 at 2 K. The magnetic structure has been investigated from low-T NPD patterns collected with a larger wavelength (λ = 2.52 Å). Magnetic peaks are observed below TN; they can be indexed with a propagation vector k = (½, 0, ½), as previously observed in other RNiO3 perovskites for the Ni sublattice. Among the three possible solutions for the magnetic structure, the first one is discarded since it would correspond to a full charge ordering (Ni2+ + Ni4+), with magnetic moments only on Ni2+ ions, not compatible with the structural findings assessing a partial charge disproportionation. The best agreement is found for a non-collinear model with two different moments in Ni1 and Ni2 sites, 1.4(1) μB, and m 0.7(1) μB at 2 K, the ordered magnetic moments lying on the a-c plane. This is similar to that found for YNiO3. In complement, the magnetic and thermal properties of LuNiO3 have been investigated. AC susceptibility curves exhibit a clear peak centered at TN = 125 K, corresponding to the establishment of the Ni antiferromagnetic structure. This is corroborated by DC susceptibility and specific heat measurements. Magnetization vs. field measurements confirm that the system is antiferromagnetic down to 2 K, without any further magnetic change. This linear behavior is also observed in the paramagnetic regime (T > TN).

Superconductivity and Phase Diagram in the Nanostructured Eutectic Ga-Ag Alloy

Here, we present a study of superconductivity in the Ga-Ag alloy embedded into porous template with pore diameter of 10 nm. The composition was close to the eutectic point in the gallium-rich range. We measured DC and AC magnetizations for temperatures from 1.8 to 10 K and magnetic fields up to 6 T. Three superconducting transitions were found at temperatures 7.05, 6.08, and 2.65 K in contrast to the bulk counterpart. Upper critical field lines were obtained. Activation barriers were evaluated from the AC data. The temperatures of the superconducting transitions were ascribed to emergence of β- and iota-Ga and of an intermetallic different from bulk Ag3Ga2. Keywords: nanostructured Ga-Ag eutectic alloy, superconducting transitions, segregated phases, DC and AC susceptibility.

Influence of Nonmagnetic Dilution on the Magnetic Properties of La1−xDyxMn1−yZnyO3 Perovskites at High Temperature

Herein, the influence of Zn nonmagnetic doping on magnetic properties above the Curie temperature of La1−x Dy x Mn1−y Zn y O3 diluted samples is studied. The Zn doping effect on the structure and distortions of MnO6 octahedra are observed, suggesting a relaxation effect of the tilting on the stress introduced by Zn doping. Magnetization versus temperature shows a transition from paramagnetic (PM) to ferromagnetic (FM) phase in the temperature range from 130 to 190 K. In the PM regime, FM spin clusters are observed by dc susceptibility and electron PM resonance (EPR). The effective moment of the clusters is obtained from the high‐temperature dc susceptibility. The effective exchange constants, J, are estimated using an open‐source program for the high‐temperature expansion (HTE) for inverse susceptibility of the spin Heisenberg model.

AC magnetic susceptibility of nanocomposites with Co-Pd particles

Frequency and magnetic field dependences of the dynamic AC susceptibility of nanocomposites based on opal matrixes with Co and Pd particles have been experimentally investigated in the temperature range from 1.8 to 300 K at several frequencies of alternating magnetic field. Comparative analysis of the magnetic field dependences of the differential DC and dynamic AC susceptibilities has been carried out. The hysteresis loops of the nanocomposite samples were measured, as well as their structure and phase composition were studied. The magnetic field dependences of the differential DC susceptibility have been found to be close to the field dependences of the dynamic AC susceptibility measured at the frequency of 1 Hz but substantially differ from the susceptibility measured at the frequency of 10 Hz and higher. This fact indicates that long relaxation times exceeding ∼ 1 s are characteristic of the substance (Co + Pd). The frequency dependences of the dynamic AC susceptibility were used to calculate the relaxation times with the Cole-Cole formula. The sample with hexagonal Co and metallic Pd has been found to have three relaxation times of about 10-3, 10-2 and 1 s. At that, the field dependences of the differential DC susceptibility differ from the field dependences of the dynamic AC susceptibility measured at the frequencies of 10, 100 Hz and 1 kHz, which, in turn, are close to each other. This means that the eddy current losses are small in comparison with the magnetization reversal losses.

Optical and Magnetic Properties of Cubic Double Perovskites Ba2RSbO6(R= Dy, Gd) Coordinated to Lattice Dynamical and Crystal‐Field Computations

Herein, optical (e.g., UV–Vis reflectance spectra, infrared and Raman spectroscopy) and magnetization properties of the double‐perovskite compounds Ba2DySbO6(BDS) and Ba2GdSbO6(BGS) are reported. Optical bandgap is determined to be 4.524 eV for BDS and 4.465 eV for BGS using Kubelka–Munk function fit to the UV–Vis spectra. The lattice dynamical calculations on the force‐field model are undertaken for assigning the observed infrared and Raman modes. The dc susceptibility does not exhibit magnetic ordering down to 2 K for the two compounds. The dc magnetization atT = 2 K does not saturate for BDS even at a magnetic field of 11 T, but saturates at 5 T to a value of 7μB/Gd3+for BGS. A frequency‐dependent cusp in the ac susceptibility appears at 3.3 K, that is unlikely generic spin‐glass‐like freezing, and may be attributed to the short‐range correlations among Dy3+‐moments in BDS. Crystal‐field (CF) computations are performed to analyze the magnetic data for BDS. The obtained CF level scheme of Dy3+ions demonstrates the observed susceptibility and isothermal magnetization curves very well. The field‐dependence of the two lowest CF levels along different principal axes does not exhibit any level crossing, consistent with the lack of ordering in Ba2DySbO6.

The Highly Frustrated 5d2 Double Perovskite Doppelgängers, SrLaMgReO6 and SrLaLiOsO6. A Comparison including Isostructural La2LiReO6.

The synthesis and characterization of the double perovskite SrLaLiOsO6 is presented. It is isostructural (P21/n) and isoelectronic (5d2) with SrLaMgReO6, which has been reported previously. The cell volumes are the same to within 1.4%: i.e., these perovskites are doppelgängers. In a previous study SrLaMgReO6 showed no sign of spin order to 2 K. New data at lower temperatures disclose a maximum in the dc susceptibility near 1.5 K. As the Curie-Weiss (C-W) temperature (Θ) for this material is -161 K, an enormous frustration index, f ≈ 100, is implied (f = |Θ|/Tord). On the other hand, SrLaLiOsO6 does not follow the C-W law over the investigated susceptibility range, 2-300 K. Fitting with an added temperature independent term (TIP) gives μeff = 1.96 μB, Θ = -102 K, and TIP = 1.01 × 10-3 emu/mol. A clear zero-field-cooled (ZFC), field-cooled (FC) divergence in the dc data occurs at ∼10 K, suggesting a much reduced frustration index, f ≈ 10, relative to SrLaMgReO6. The real part of the ac susceptibility data, χ'max, shows a frequency shift that is consistent with a spin glass ground state according to the Mydosh criterion. Heat capacity data for SrLaLiOsO6 show no sign of a λ peak at 10 K and a linear dependence on temperature below 10 K, also supporting a spin glass ground state. A spin frozen ground state for SrLaMgReO6 could not be established from χ' data due to a much weaker signal. Nonetheless, the 10-fold difference in f between these doppelgänger materials is remarkable. It is possible that the enhanced covalency with the oxide ligands for Os6+ relative to Re5+ plays a major role here. Finally, a comparison with isostructural La2LiReO6 (with a much smaller f ≈ 4) is made and a correlation between the frustration level and the sense of the local distortion of the Re(Os)-O octahedron is pointed out.

Magnetic properties and evidence of a new spin-glass transition induced by Mn-doping in Tb2NiSi3

It is extremely rare for the coexistence of two spin glass transitions in single phase materials. In the present paper, the structure and magnetic properties of Tb2Ni0.8Mn0.2Si3 were investigated. For comparison, the corresponding experimental results of Tb2NiSi3 compound were also provided. In the temperature dependence of dc susceptibility measurements, there are two anomaly transitions for both Tb2Ni0.8Mn0.2Si3 and Tb2NiSi3. Further studies on the frequency dependence of ac susceptibility show a new spin-glass transition at 14 K in Tb2Ni0.8Mn0.2Si3, except for the spin-glass transition at 8 K inheriting from Tb2NiSi3. This new spin-glass transition in Tb2Ni0.8Mn0.2Si3 is absent in Tb2NiSi3. It takes place below the long-range magnetic ordered phase transition and shows cluster spin glass behaviors, and it is attributed to the introduction of Mn ions into the intermetallic compound.

Magnetic dynamics of NiMn2O4 spinel produced by a simple aqueous sol–gel route

Polycrystalline nickel manganite was prepared by a simple sol–gel method from an aqueous solution of metal chlorides containing sorbitol as a chelating agent. X-ray diffraction and Rietveld refinement show a spinel-type crystalline structure, space group Fd3¯m, and a minor (~3%) phase of rock salt structure assigned to NiO. XPS measurement shows a typical manganite electronic structure with Mn in the oxidation states Mn2+, Mn3+, and Mn4+. The zero-field-cooled and field-cooled magnetization curves measured under low magnetic fields display irreversibility and an asymmetric hysteresis evidencing some exchange bias. Field dependent DC susceptibility above Curie temperature put into evidence a competition of short ranged ferro and antiferromagnetic interactions. AC in-phase susceptibility shows a frequency independent sharp peak at the ferromagnetic phase transition (97 K) and a broad maximum at lower temperature. These maxima show a weak frequency dependence in the out-phase component. Cole–Cole plot reveals at least two magnetic relaxation processes.

Heisenberg Spin Chains via Chalcogen Bonding: Noncovalent S···O Contacts Enable Long-Range Magnetic Order.

The new radical ligand 5,8-dimethyl-1,4-dioxonaphtho[2,3-d][1,2,3]dithiazolyl (1) is reported. Two crystal polymorphs, 1α and 1β, differing in their pancake-bonded dimerization motif and S···O contact network, are identified. The self-assembly of Mn(II) metal ions with 1 leads to the formation of [Mn(hfac)2]3(1)2 that exhibits a Mn(II)-radical-Mn(II)-radical-Mn(II) linear arrangement of three Mn(hfac)2 units bridged by two radical ligands (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). Characterization by single-crystal X-ray diffraction of this Mn(II) complex packing structure reveals close noncovalent S···O contacts between the [Mn(hfac)2]3(1)2 units in one dimension along the b-c direction. The magnetic properties of the coordination complex are characterized by dc and ac susceptibility measurements on a microcrystalline solid. The magnetic data down to 4.8 K indicate the presence of effective ferromagnetic interactions (J/kB = +0.16 K) between the molecular ST = 13/2 units along the supramolecular chain involving noncovalent S···O contacts. Below 2.9 K, a non-zero out-of-phase component appears in the ac susceptibility, indicating the presence of a three-dimensional magnetic phase transition.

Cluster-glass behavior in the two-dimensional triangular lattice Ising-spin compound Li2Mn3O7

We present the detailed structural and magnetic properties of ${\mathrm{Li}}_{2}{\mathrm{Mn}}_{3}{\mathrm{O}}_{7}$ from powder x-ray diffraction (XRD), dc susceptibility, heat capacity, ac susceptibility, thermoremanent magnetization, magnetic memory, and exchange bias effect. Rietveld refinement of XRD data reveals that this compound has a rhombhohedral structure composed of a layered triangular lattice. Onset of spin-glass transition was confirmed by dc magnetization and ac susceptibility measurements. Dynamic scaling laws were used to analyze and classify the glassy behavior of the compound. Magnetic field dependence of irreversible temperature follows the Almeida-Thouless line, which is characteristic for an Ising spin-glass system. Fitting of the frequency-dependent freezing temperature with a power law results in $z{\ensuremath{\nu}}^{\ensuremath{'}}=4.06\ifmmode\pm\else\textpm\fi{}0.06$, which indicates the critical exponent of the sluggish spin dynamics and ${\ensuremath{\tau}}_{0}=4.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ s is a characteristic time scale for a single spin-flip. Further evidence of cluster-glass behavior comes from the frequency dependence of the freezing temperature fitted with the Vogel-Fulcher law, which considers interaction between bigger magnetic entities. Values of fitting parameters are ${E}_{a}/{k}_{B}=27.62$ K and ${T}_{0}=9.57$ K, which confirm cluster-glass behavior. The presence of magnetic relaxation below freezing temperature and the magnetic memory effect confirms the nonequilibrium dynamics of the system through a number of metastable states. Moreover, observation of the exchange bias effect reflects the presence of intrinsic phase inhomogeneity. These results indicate that the triangular lattice causes a disordered ground state as a result of competing exchange interactions.