Dc Susceptibility Research Articles

Cluster glass transition and relaxation in the random spinel CoGa2O4

We report magnetic properties in the random spinel magnet ${\mathrm{CoGa}}_{2}{\mathrm{O}}_{4}$. Rietveld analysis of the x-ray diffraction profile for ${\mathrm{CoGa}}_{2}{\mathrm{O}}_{4}$ reveals that the Co and Ga ions are distributed randomly in the tetrahedral $A$ sites and octahedral $B$ sites in the cubic spinel structure. ${\mathrm{CoGa}}_{2}{\mathrm{O}}_{4}$ exhibits a spin-glass transition at ${T}_{\mathrm{SG}}=8.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ that is confirmed by measurements of the dc and ac susceptibilities and thermoremanent magnetization (TRM) that develops below ${T}_{\mathrm{SG}}$. From the frequency dependence of the freezing temperature ${T}_{\mathrm{f}}$ for ${\mathrm{CoGa}}_{2}{\mathrm{O}}_{4}$, it is indicated that the relaxation time $\ensuremath{\tau}(T)$ follows a Vogel-Fulcher law $\ensuremath{\tau}={\ensuremath{\tau}}_{0}\mathrm{exp}[\ensuremath{-}{E}_{a}/{k}_{\mathrm{B}}(T\ensuremath{-}{T}_{0})]$. An analysis of specific heat suggested that a doublet ground state of the octahedrally coordinated ${\mathrm{Co}}^{2+}$ was stabilized by spin-orbit and crystal field couplings. The relaxation rate of TRM is considerably enhanced at ${T}_{\mathrm{SG}}$ and decays rapidly above and below ${T}_{\mathrm{SG}}$. The time course of TRM is reproduced by nonexponential relaxation forms, such as a stretched exponential (Kohlrausch) as well as Ogielski and Weron relaxation forms. This behavior is displayed universally in glass systems, and the characteristic parameters associated with these functions were reasonable.

Study of the magnetic properties of YbMn2Sb2 single crystals by [formula omitted]SR

The crystal growth and the structural, transport and magnetic properties of YbMn2Sb2 single crystals are reported. The crystals show a trigonal symmetry of La2O2S-type structure (space group P3¯m1, N. 164, hP5), where corrugated honeycomb layers of MnSb are separated by Yb atoms. No structural phase transition was observed down to 22 K. The resistivity measurements show a predominantly insulating behavior. The combined resistivity, dc susceptibility and specific heat measurements confirm successive features at 40 K, 116 K and 225 K, being the phase transition at TN=116 K due to the Mn+2 lattice antiferromagnetic ordering. Muon spin rotation experiments (μSR) reveal a more complicated scenario, with temperature dependence of the magnetic volume fraction reflecting a static and strongly disordered magnetic ground state. The role of spin–lattice coupling and its relationship with exchange interactions between Mn moments is discussed as a possible cause of the magnetic behavior observed.

Magnetic structure investigation of the intercalated transition metal dichalcogenide V1/3NbS2

We investigate the temperature evolution of the magnetic structure of ${\mathrm{V}}_{1/3}{\mathrm{NbS}}_{2}$ using neutron diffraction techniques. We find that ${\mathrm{V}}_{1/3}{\mathrm{NbS}}_{2}$ has two propagation vectors: ${\mathbf{k}}_{\mathbf{0}}=(0,0,0)$ and ${\mathbf{k}}_{\mathbf{1}}=(0,0,\frac{1}{3})$. The ${\mathbf{k}}_{\mathbf{0}}$ vector can be associated with an antiferromagnetic ordering of in-plane moments with a refined value of $0.90(5){\ensuremath{\mu}}_{\mathrm{B}}$, and ${\mathbf{k}}_{\mathbf{1}}$ can be associated with moments along the $c$ axis in an up-down-down configuration with refined values of $1.21(12){\ensuremath{\mu}}_{\mathrm{B}}$ and $0.61(6){\ensuremath{\mu}}_{\mathrm{B}}$. Both ${\mathbf{k}}_{\mathbf{0}}$ and ${\mathbf{k}}_{\mathbf{1}}$ magnetic components couple with an out-of-plane ferromagnetic moment consistent with magnetization data. Furthermore, single-crystal neutron diffraction shows evidence of diffuse magnetic scattering between the (010) and ($01\ifmmode\pm\else\textpm\fi{}\frac{1}{3}$) Bragg peaks. We also characterize the field and temperature evolution of the magnetic structure in ${\mathrm{V}}_{1/3}{\mathrm{NbS}}_{2}$ by magnetic susceptibility and heat capacity measurements. The dc susceptibility measurements give an antiferromagnetic transition temperature of ${T}_{\mathrm{N}}=50$ K, and the field scans reveal that the moment does not saturate at magnetic fields up to 100 kOe.

Double magnetic phase transitions and magnetotransport anomalies in a new compound Gd2AgSi3

Dc and ac–magnetic susceptibility (χ), specific heat (CP), electrical resistivity (ρ) and magnetoresistance measurements performed on the new polycrystalline compound Gd2AgSi3, crystallizing in the α–ThSi2 tetragonal structure, are reported. Two magnetic phase transitions were observed in dc and ac susceptibility, specific heat and resistivity measurements at temperatures TN1=11 K and TN2=20 K, despite a single site occupied by Gd atom, which is an indication of the complex magnetic behavior. Gd2AgSi3 turns out be one of the rare Gd compound in which a minimum is observed in the temperature dependence of resistivity in the paramagnetic state and also negative magnetoresistance over a wide temperature range (above TN2), mimicking the behavior of exotic Gd2PdSi3, in this ternary family. The isothermal magnetic entropy change, adiabatic temperature change, and refrigerant capacity reach a value of 9.5 J/kg-K, 7.5 K and 302 J/kg, respectively for the change of magnetic field 0-9 T.

Linear shaped hetero-metallic [Zn2Ln4] clusters with Schiff base ligand: Synthesis, characterization and magnetic properties

A series of isostructural 3d–4f coordination clusters (CCs) [Zn2Ln4(L1)4(L2)2(OAc)2(N3)2] [Na2(OH2)2(NO3)3.2(N3)0.8]∙2MeCN, where Ln = Dy (1), Ho (2), Er (3), Tm (4), and Yb (5), L1 = 6-Methoxy-2-(2-pyridylmethyliminomethyl)phenol and L2 = (E)-2-methoxy-6-(2-((3-methoxy-2-oxidobenzylidene)amino)-1-oxido-2-(pyridin-2-yl)ethyl)phenolate has been synthesised and structurally characterised. The magnetic properties of 1–5 have been investigated using dc and ac susceptibility measurements. The paramagnetic metal ions within the clusters are weakly antiferromagnetically coupled, with the Er and Dy compounds displaying slow relaxation of their magnetisation. This is the first report of this versatile ligand being used to target 3d–4f coordination clusters.

Non-Fermi liquid behavior and signature of Griffiths phase in Ni–Cr binary alloy

Detailed magnetic, electrical, and thermal property measurements have been carried out on Ni100−xCrx binary alloys, mainly to study the effect of Cr. The following points emerge from this study: with the increase in Cr concentration, magnetic moment and Curie temperature linearly decreased and the ferromagnetic order is completely suppressed at the critical concentration (xcr ≈ 12.16 ± 0.03). The Rhodes–Wohlfarth ratio increases as the concentration approaches xcr, suggesting a weak itinerant ferromagnetic character of NiCr compositions (x < xcr). Analysis of low-temperature electrical resistivity and specific heat data suggests that the spin fluctuation’s contribution increases and the Fermi-liquid behavior breaks down as the concentration approaches xcr. For x ∼ xcr, the dc susceptibility χ(T) deviates from the Curie–Weiss law reminiscent to that of the Griffiths phase. The low-temperature magnetic isotherms of Ni–Cr follow power law, M(H)=M0+dλHλ, and the non-universal exponent (λ) shows a minimum at xcr ∼ 12. Further, temperature dependence of magnetization studies also support the presence of the quantum Griffiths phase, similar to that reported in the Ni–V alloy system. The temperature dependencies of the electrical resistivity, magnetization, and specific heat follow the theoretical predictions of a quantum critical point within experimental uncertainties.

Griffiths phase and spontaneous magnetization in polycrystalline Co50V34Ga16 alloy

In this work, we synthesized the Co50V34Ga16 alloy by directional solidification technique. Interestingly, the Griffiths phase was found in Co-V-Ga alloy for the first time. Using the DSC curve and the inverse DC susceptibility (χ−1) in the high temperature region, the spontaneous magnetization revealed the existence of Griffiths phase in the high temperature region. And then, according to Arrott plot, the phase transition was determined around the TC. Modified form of the Bean-Rodbell model, considering a shape memory alloy material with compressibility, spin and spin density, one defines the parameter ε, which is 0.26, (ε < 1), further confirmed the transition type around TC. At low temperature, spin wave excitation (Heisenberg ferromagnetic type) was used to study the dependence of spontaneous magnetization on temperature to investigate half metallicity.

Exotic magnetic behavior with intrinsic and extrinsic magnetodielectric effects in Pr2CuMnO6

We present a systematic exploration of structural, electrical transport, thermomagnetic, and magneto–dielectric properties of polycrystalline perovskite, Pr2CuMnO6. Powder X-ray diffraction confirms the orthorhombic crystal structure with the Pbnm space group. The electrical transport studies reveal high resistivity (1.34 ×104 ohm–meter at 123 K) of the compound with semiconducting type temperature variation, and the conduction process follows the variable range hopping of polarons. Magnetization measurements reveal the magnetic ordering at 55 K followed by a cluster glass phase below 22 K. Frozen magnetic phase at lower temperature results from competing short-range FM/AFM interactions due to atomically disordered mixed valent B-site ions (Cu2+/3+ and Mn3+/4+). Inverse DC susceptibility reveals the observation of Griffiths phase above the glassy transition, extending up to 66 K. Magnetodielectric (MD) analysis reveals intrinsic MD effect (20 – 100 K) due to spin-lattice coupling followed by extrinsic MD effect (100 – 180 K) due to Maxwell–Wagner contribution.

Néel ordering in the distorted honeycomb pyrosilicate: C–Er2Si2O7

The rare-earth pyrosilicate family of compounds (RE2Si2O7) hosts a variety of polymorphs, some with honeycomb-like geometries of the rare-earth sublattices, and the magnetism has yet to be deeply explored in many of the cases. Here we report on the ground state properties of C–Er2Si2O7. C–Er2Si2O7 crystallizes in the C2/m space group and the Er3+ atoms form a distorted honeycomb lattice in the a–b plane. We have utilized specific heat, DC susceptibility, and neutron diffraction measurements to characterize C–Er2Si2O7. Our specific heat and DC susceptibility measurements show signatures of antiferromagnetic ordering at 2.3 K. Neutron powder diffraction confirms this transition temperature and the relative intensities of the magnetic Bragg peaks are consistent with a collinear Néel state in the magnetic space group C2’/m, with ordered moment of 6.61 μ B canted 13° away from the c-axis toward the a-axis. These results are discussed in relation to the isostructural quantum dimer magnet compound Yb2Si2O7.

A Scaled Effective Medium Theory for Calculation of Resonant and Relaxation Frequency in Magnetic Composites

Scaled Effective Medium Theory (ScEMT) is applied to predict magnetic resonant and relaxation frequency in polymer-magnetic particle composites with favorable comparison to measured data. A single scaling function is identified that uses magnetic particulate resonant and relaxation frequencies, or magnetization and anisotropy field, volume fraction and DC susceptibility as predicted by ScEMT. Previous publications demonstrated that ScEMT improved the prediction of DC susceptibility as compared to classical models. Maxwell-Garnett (MGT) and Coherent Model Approximation (CMA) serve as theoretical baselines for comparison. However, both require separate scaling functions in their prediction of resonant and relaxation. Measured data are presented that suggest a single scaling function of ScEMT is sufficient to calculate both parameters. The paper emphasizes the application of the models and shows a wide range of particulate chemistries. ScEMT calculates susceptibility, resonant and relaxation frequency that agree with measurement. The paper concludes by predicting dispersive permeability that represents improvement over both CMA and MGT models. Future studies will address formulation of an EMT model (s) that describe mixtures of hard and soft magnetic materials mixed in a polymer composite. EMT for composite dielectric properties will be expanded to address the chaining. Early results of that effort will be reported in a separate paper.

Enhancing the barrier height for magnetization reversal in 4d/4f RuIII2LnIII2 "butterfly" single molecule magnets (Ln = Gd, Dy) via targeted structural alterations.

A series of 4d-4f {RuIII2DyIII2} and {RuIII2GdIII2} 'butterfly' (rhombohedral) complexes have been synthesized and characterized and their magnetic properties investigated. Earlier, we have reported the first 4d/4f SMM - [RuIII2DyIII2(OMe)2(O2CPh)4(mdea)2(NO3)2] (1Dy) with a Ueff value of 10.7 cm-1. As the structural distortion around the DyIII centres and the RuIII⋯DyIII exchange interactions are key to enhancing the anisotropy, in this work we have synthesised three more {Ru2Dy2} butterfly complexes where structural alteration around the DyIII centres and alterations to the bridging groups are performed with an aim to improve the magnetic properties. The new complexes reported here are [Ru2Dy2(OMe)2(O2C(4-Me-Ph)4(mdea)2(MeOH)4], 2Dy, [Ru2Dy2(OMe)2(O2C(2-Cl,4,5-F-Ph)4(mdea)2(NO3)2], 3Dy, and an acac derivative [Ru2Dy2(OMe)2(acac)4(NO3)2(edea)2], 4Dy, where acac- = acetylacetonate, edea2- = N-ethyldiethanolamine dianion. Complex 2Dy describes alteration in the DyIII centers, while complexes 3Dy and 4Dy are aimed to alter the RuIII⋯DyIII exchange pathways. To ascertain the 4d-4f exchange, the Gd-analogues of 1Dy and 4Dy were synthesised [Ru2Gd2(OMe)2(O2CPh)4(mdea)2(NO3)2], 1Gd, [Ru2Gd2(OMe)2(acac)4(NO3)2(edea)2], 4Gd. Both ac and dc susceptibility studies were performed on all these complexes, and out-of-phase signals were observed for 3Dy in zero-field while 2Dy and 4Dy show out-of-phase signals in the presence of an applied field. Complex 3Dy reveals a barrier height Ueff of 45 K. To understand the difference in the magnetic dynamic behavior compared to our earlier reported {RuIII2DyIII2} analogue, detailed theoretical calculations based on ab initio CASSCF/RASSI-SO calculations have been performed. Calculations reveal that the JRu⋯Dy value varies from -1.8 cm-1 (4Dy) to -2.4 cm-1 (3Dy). These values are also affirmed by DFT calculations performed on the corresponding GdIII analogues. The origin of the largest barrier and observation of slow magnetic relaxation in 3Dy is routed back to the stronger single-ion anisotropy and stronger JRu⋯Dy exchange which quenches the QTM effects more efficiently. This study thus paves the way forward to tune local structure around the LnIII center and the exchange pathway to enhance the SMM characteristics in other {3d-4f}/{4d-4f} SMMs.

Coexistence of non-Fermi liquid behavior and biquadratic exchange coupling in La-substituted CeGe: Nonlinear susceptibility and DFT+DMFT study

Studies connected with the investigations of non-Fermi liquid (NFL) systems continue to attract interest in condensed matter physics community. Understanding the anomalous physical properties exhibited by such systems and its related electronic structures is one of the central research topics in this area. In this context, Ce-based and Ce-site diluted (with non-magnetic ions) compounds provide a fertile playground. Here, we present a detailed study of non-linear DC susceptibility and combined density functional theory plus dynamical mean field theory (DFT+DMFT) on Ce0.24La0.76Ge. Theoretical investigation of 4f partial density of states, local susceptibility and self-energy demonstrates the presence of NFL behavior which is associated with fluctuating local moments. Non-linear DC susceptibility studies on this compound reveal that the transition from NFL state to the new phase is due to development of the bi-quadratic exchange coupling and it obeys the non-linear susceptibility scaling. Under the application of magnetic fields, local moments interact spatially through conduction electrons resulting in magnetic fluctuations. Our studies point to the fact that the origin of the observed bi-quadratic exchange coupling is due to the spatial magnetic fluctuations.

Sample Dependence of Magnetism in the Next-Generation Cathode Material LiNi0.8Mn0.1Co0.1O2.

We present a structural and magnetic study of two batches of polycrystalline LiNi0.8Mn0.1Co0.1O2 (commonly known as Li NMC 811), a Ni-rich Li ion battery cathode material, using elemental analysis, X-ray and neutron diffraction, magnetometry, and polarized neutron scattering measurements. We find that the samples, labeled S1 and S2, have the composition Li1-xNi0.9+x-yMnyCo0.1O2, with x = 0.025(2), y = 0.120(2) for S1 and x = 0.002(2), y = 0.094(2) for S2, corresponding to different concentrations of magnetic ions and excess Ni2+ in the Li+ layers. Both samples show a peak in the zero-field-cooled (ZFC) dc susceptibility at 8.0(2) K, but the temperature at which the ZFC and FC (field-cooled) curves deviate is substantially different: 64(2) K for S1 and 122(2) K for S2. The ac susceptibility measurements show that the transition for S1 shifts with frequency whereas no such shift is observed for S2 within the resolution of our measurements. Our results demonstrate the sample dependence of magnetic properties in Li NMC 811, consistent with previous reports on the parent material LiNiO2. We further establish that a combination of experimental techniques is necessary to accurately determine the chemical composition of next-generation battery materials with multiple cations.

Dynamic spin freezing and magnetic memory effect in ensembles of interacting anisotropic magnetic nanoparticles

We explore the influence of demagnetization interaction on magnetic memory effect by varying organization geometry of anisotropic ZnFe$_2$O$_4$ nanoparticles in an ensemble. The static and dynamic behaviour of two differently organized ensembles, compact ensemble (CE) and hollow core ensemble (HCE), are extensively studied by both dc and ac susceptibility, magnetic memory effect and spin relaxation. The frequency-dependence peak shifting of freezing temperature in both the systems is analyzed properly with the help of two dynamic scaling models: Vogel-Fulcher law and power law. Presence of cluster spin-glass phase is reflected from Vogel-Fulcher temperature $T_0$ $\simeq$ 142.58 K for CE, $\simeq$ 97 K for HCE and characteristic time constant $\tau_0$ $\simeq$ $8.85\times10^{-9}$ s for CE, $\simeq$ $3.8\times10^{-10}$ s for HCE; along with $\delta$T$_{Th}$ $\sim$ 0.1 for CE and 0.2 for HCE. The power law fitting with dynamic exponent $zv'$ = 6.2 $\pm$ 1.1 for CE, 6.3 $\pm$ 0.5 for HCE and single spin flip $\tau^*$ $\simeq$ $7.7\times10^{-11}$ s for CE, $\simeq$ $1.3\times10^{-10}$ s for HCE provide firm confirmation of cluster spin-glass phase. The progressive spin freezing across multiple metastable states with prominent memory effects is reflected in both the systems via nonequilibrium dynamics study. The hollow core geometry with anisotropic nanoparticles on surface with closer proximity leads to complex anisotropy energy landscape with enhanced demagnetizing field resulting highly frustrated surface spins. As a consequence, more prominent magnetic memory effect is observed in HCE with higher activation energy, reduced blocking temperature and enhanced coercivity than that of CE.

Magnetic anomalies associated with domain wall freezing and coupled electron hopping in magnetite nanorods

Magnetite has fascinated researchers for decades, due to its wide range of applications from spintronics to biomedicine. Despite a large body of works aimed at its magnetic properties, no consensus has been reached on the physical origin of the low temperature magnetic anomalies observed in magnetite. Although, a lot of work has been done in studying magnetite nanoparticles, but studies on the low temperature anomalies in those nanoparticles still remains unresearched. We report on the observation of the low temperature magnetic anomalies in highly crystalline, stoichiometric Fe3O4 nanorods and relate them to the coupled electron hopping relaxation process and domain wall motion. Both DC and AC susceptibility show the presence of a hump around 35 K, which is associated with the relaxation of Fe+2 extra electrons. Radio-frequency transverse susceptibility (TS) measurements indicated a noticeable increase in anisotropy field below ~ 25 K, which is attributed to the rearrangement of Fe+2 electrons in the octahedral sites. TS experiments also revealed the domain wall freezing below ~ 35 K. Our combined DC, AC and TS susceptibility studies shed light on the complex nature of the low-temperature magnetic behavior in nanostructured magnetite.

Pressure dependence of the Griffiths-like phase in 5:4 intermetallics

We report a study of the effect of hydrostatic pressure (P) on the Griffiths-like phase in selected compounds of the ${R}_{5}{({\mathrm{Si}}_{x}{\mathrm{Ge}}_{1}\ensuremath{-}x)}_{4}$ family of alloys (${\mathrm{Tb}}_{4.925}{\mathrm{La}}_{0.075}{\mathrm{Si}}_{2}{\mathrm{Ge}}_{2}$ and ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$) which present either the ${\mathrm{Gd}}_{5}{\mathrm{Si}}_{2}{\mathrm{Ge}}_{2}$-type (monoclinic, M) or the ${\mathrm{Sm}}_{5}{\mathrm{Ge}}_{4}$-type [orthorhombic-II, O(II)] structural phases at room temperature. The downward deviation in the inverse low-field dc susceptibility ${\ensuremath{\chi}}_{dc}^{\ensuremath{-}1}$ from the Curie-Weiss law below a characteristic temperature ${T}_{G}$ indicates that the Griffiths-like phase exists at pressures up to 10 kbar. From the obtained T-P phase diagrams, the pressure coefficient of the Griffiths-like temperature, ${dT}_{G}/dP$, has been determined. These results are compared with those obtained in ${\mathrm{Dy}}_{5}{\mathrm{Si}}_{3}\mathrm{Ge}$ in a previous work. The ${dT}_{G}/dP$ coefficient is strongly dependent on the nature (first or second order) of the long-range order (FM or AFM) transition. This effect can be ascribed to a different structural character of the clusters within the Griffiths phase. A ratio of $\ensuremath{\sim}0.5$ between the ${dT}_{G}/dP$ and the pressure coefficient of long-range magnetic ordering temperatures, ${dT}_{C,N}/dP$ (${T}_{C}$, ferromagnetic; ${T}_{N}$, antiferromagnetic), is found in all the studied compounds.

Heterometallic Group 4-Lanthanide Oxo-alkoxide Precursors for Synthesis of Binary Oxide Nanomaterials.

In this study, an efficient procedure for the synthesis of uncommon group 4-lanthanide oxo-alkoxide derivatives was developed. Heterometallic clusters with the structures [La2Ti4(μ4-O)2(μ3-OEt)2(μ-OEt)8(OEt)6(Cl)2(HOEt)2] (1), [La2Zr2(μ3-O)(μ-OEt)5(μ-Cl)(OEt)2(HOEt)4(Cl)4]n (2), [La2Hf2(μ3-O)(μ-OEt)5(μ-Cl)(OEt)2(HOEt)4(Cl)4]n (3), [Nd2Ti4(μ4-O)2(μ3-OEt)2(μ-OEt)8(OEt)6(HOEt)2(Cl)2] (4), [Nd4Zr4(μ3-O)2(μ-OEt)10(μ-Cl)4(OEt)8(HOEt)10(Cl)2] (5), and [Nd4Hf4(μ3-O)2(μ-OEt)10(μ-Cl)4(OEt)8(HOEt)10(Cl)2] (6) were synthesized via the reaction of a metallocene dichloride, Cp2M'Cl2 (where M' = Ti, Zr, and Hf), and metallic lanthanum or neodymium in the presence of excess ethanol. This procedure gave crystalline precursors with molecular stoichiometries suitable for obtaining group 4-lanthanide oxide materials. Compounds 1-6 were examined by analytical and spectroscopic techniques and single-crystal X-ray diffraction. The magnetic properties of 5 and 6 were investigated by using direct and alternating current (dc and ac) susceptibility measurements. The results indicated weak antiferromagnetic interactions between NdIII ions and a field-supported slow magnetic relaxation. Lanthanum-titanium compound 1 decomposed at 950 °C to give the perovskite compound La0.66TiO3 and small amounts of rutile TiO2. Under the same conditions, 4 decomposed to give a mixture of Nd4Ti9O24 and Nd0.66TiO3. When 4 was calcined at 1300 °C, decomposition of Nd4Ti9O24 to Nd0.66TiO3 and TiO2 was observed. Calcination of 2, 3, 5, and 6 at 950-1500 °C led to the selective formation of heterometallic La2Zr2O7, La2Hf2O7, Nd2Zr2O7, and Nd2Hf2O7 phases, respectively.

Griffiths phase-like exponents in the hidden-order state of URu2Si2

We report electrical resistivity, magnetic susceptibility, and specific heat measurements of high-quality URu2Si2 single crystals at ambient pressure, in the hidden-order (HO) region of the phase diagram. An amazing power-law behavior is observed, for both DC susceptibility and specific heat, establishing the Griffiths model for the HO phase. The Griffiths phase is characterized by residual short-range correlations on the collapse of the long-range large-moment antiferromagnetic (LMAFM) phase due to the dilution effects. The existence of cluster-like spins is intrinsic, as evidenced by the frequency dispersion of AC susceptibility and the relaxation of magnetoresistance. On account of the freezing of magnetic clusters, an unidirectional anisotropy of the resistivity in rotating magnetic fields is detected, which naturally explains any possible broken symmetries in tiny and clean crystals. In this manner, the HO phase of URu2Si2 is intimately related to the LMAFM phase. The proposal of Griffiths phase as an alternative of the HO phase is very promising, which may open a new route into the understanding of exotic electronic states in correlated matter.

Magnetic ordering and spin dynamics in theS=52staggered triangular lattice antiferromagnetBa2MnTeO6

We report studies of the magnetic properties of a staggered stacked triangular lattice Ba$_2$MnTeO$_6$ using magnetic susceptibility, specific heat, neutron powder diffraction and inelastic neutron scattering measurements, as well as first principles density functional theory calculations. Neutron diffraction measurements reveal an antiferromagnetic order with a propagated vector $\textbf{\emph{k}}=(0.5, 0.5, 0)$ and N{\'{e}}el transition temperature of $T_\text{N}\approx20$ K. The dominant interaction derived from the Curie-Weiss fitting to the inverse DC susceptibility is antiferromagnetic. Through modelling the INS spectrum with the linear spin wave theory, the magnetic exchange interactions for the nearest intralayer, nearest interlayer, and next nearest interlayer are determined to be $J_1=0.27(3),J_2=0.27(3),$ and $J_3=-0.05(1)$ meV, respectively, and a small value of easy-axis anisotropy of $D_{zz}=-0.01$ meV is introduced. We derive a magnetic phase diagram that reveals that it is the competition between $J_1, J_2$, and $J_3$ that stabilizes the collinear stripe-type antiferromagnetic order.

Aging effect on the magnetic properties of Mn12-stearate single-molecule magnets anchored onto the surface of spherical silica nanoparticles

The effects of structural and magnetic aging in Mn12-stearate single-molecule magnets (SMMs) deposited on the surface of 300 nm spherical silica nanoparticles were investigated. It was pointed out that the molecules attached on the surface preserve its magnetic characteristics (hysteresis in M(H) loops and slow magnetic relaxation). However, the observed magnetic properties evolve over time revealing significant changes. DC susceptibility studies together with Raman spectroscopy were applied to investigate this aging effect. Measurements over 221 days period showed change of magnetic parameters: exponential decrease of coercive field from 4.5 kOe to 150 Oe (with τc = 33 days) and remnant magnetization from 0.072 emu/g to 0.0022 emu/g (with τrem = 46 days). Time-dependent magnetization measurements have indicated the presence of slow magnetic relaxations (Ueff = 33.6 K) for the fresh sample in temperature range 2.0–3.0 K. However, the aged sample (221 days after synthesis) did not show typical relaxations, but a magnetic viscosity behavior was observed. The Raman measurements revealed partial decomposition of stearate groups and possible formation of hydroxyl system over time, which explain the observed magnetic changes.