Cluster Glass Transition Research Articles

Existence of complex magnetic ground state and topological Hall effect in centrosymmetric silicide DyScSi

Topological Hall effect (THE) originating from non-trivial spin arrangements in magnetic materials has been extensively investigated in recent years. In this context, a centrosymmetric ternary silicide, DyScSi, is explored. Here we show that, a complex magnetic ground state drives THE in a centrosymmetric system. Temperature dependent magnetisation and neutron diffraction results establish the presence of commensurate antiferromagnetic (AFM) phase around 92 K, followed by an incommensurate AFM phase below 40 K. Additionally, two cluster glass transitions near 20 and 8 K, are also noted. These observed features arise due competing AFM and FM interactions. In conjunction with this, a finite contribution of THE is also observed in the intermediate field regime (8–30 kOe), at low temperature in DyScSi. The behaviour of this silicide appears to be fascinating in terms of interplay between complex magnetic ground state and THE in centrosymmetric structure.

Ground-state degeneracy and complex magnetism of geometrically frustrated Gd2Ir0.97Si2.97

A new triangular-lattice intermetallic compound ${\mathrm{Gd}}_{2}{\mathrm{Ir}}_{0.97}{\mathrm{Si}}_{2.97}$ was successfully synthesized as single phase by deliberately introducing vacancies. Theoretical analysis suggests that the ground state is competing with several low-energy spin configurations due to magnetic frustration on a nearly ideal triangular lattice. Despite a number of competing magnetic states, the compound exhibits long-range antiferromagnetic order at 16 K, a long-range ferrimagnetic transition at 6.5 K, and a reentrant cluster-glass transition below ${T}_{f}$ $\ensuremath{\sim}$ 3 K. The complex magnetism in the compound could be correlated with competing antiferromagnetic and ferrimagnetic structures predicted theoretically.

Evidence for cluster glass ground state in the potential giant dielectric constant material Ba(Fe1/2Sn1/2)O3-δ

We report the magnetic ground state of the technologically important giant dielectric constant material Ba(Fe1/2Sn1/2)O3-δ (BFSO) using detailed dc and ac magnetization and specific heat measurements. Our careful x-ray diffraction analysis confirms that BFSO is single phase and crystallizes in the cubic structure with the Pm3¯m space group. Temperature-dependent dc susceptibility measurements reveal that magnetic irreversibility sets in below Tirr ~ 18 K. In addition, the zero-field cooled susceptibility exhibits a peak at the freezing temperature Tf ~ 16 K, which is also characterized by a frequency dispersion in ac susceptibility measurements. This data also confirms to the critical slowing down model with cluster-glass transition temperature TG ~15.7 K and characteristic relaxation time τo ~10−7 s. The magnetic field dependence of the freezing temperature Tf obeys de Almeida-Thouless line in the H-T plane. The presence of aging effect and extremely slow time decay of thermoremanent magnetization is also observed below Tf. The magnetic contribution to the specific heat (Cm) exhibits a linear temperature dependence below Tf. All these observations unambiguously confirm a cluster-glass magnetic ground state in this system.

Double glassy states and large spontaneous and conventional exchange bias in La1.5Ca0.5CoFeO6 ferrimagnetic double perovskite

The structural and magnetic properties of hole doped double perovskite La1.5Ca0.5CoFeO6 have been investigated by measuring x-ray photoemission spectroscopy, neutron powder diffraction and magnetization. A ferrimagnetic transition is observed at T C∼ 167 K. The presence of anti-site disorder (ASD) in La1.5Ca0.5CoFeO6 has also been demonstrated. Double re-entrant cluster glass transitions (T 1∼ 11 K and TS ∼ 35 K) were observed which has been attributed to the ASD effect. The presence of both large spontaneous exchange bias H SEB ∼ 2.106 kOe and giant conventional exchange bias H CEB ∼ 1.56 T at 5 K has also been observed which can be attributed to the coexistence of long range magnetic ordering and glassy state. The experimental observations were explained with the results obtained by the density functional theory calculation. The presence of double glassy states, large exchange-bias effect and different magnetic phases make this system a potential candidate for spintronic applications.

Reentrant double glassy states and simultaneous presence of short- and long-range ordering in metamagnetic Co-doped Bi0·5La0·5Fe0·5Mn0·5O3 multiferroic

A study of the structural and magnetic properties of Bi0·5La0·5Fe0·45Co0·05Mn0·5O3 is presented in the article. We report the rare observations of two glassy transitions below the long-range ordering temperature along with the metamagnetic transitions at low temperatures. Frequency and DC field dependence of AC susceptibility and isothermal relaxation of remnant magnetization studies have all shown the slow spin dynamics for the compound. Interestingly, in the glass phase of the materials, metamagnetic transitions of the antiferromagnetic spins were found which indicate the coexistence of the long-range ordered phase along with the short-range ordered glassy phase. The double cluster glass phases can be comprehended, from the relaxations of the spin clusters arising from the competing magnetic interactions present in the system. Moreover, the roles of additional exchange interactions which are brought to the system by Co doping are also considered in explaining the observed double cluster glass transitions.

Evidence of room temperature magnetodielectric and cluster glass behavior of Sr substituted Y-type Ba2Mg2Fe11.48Mn0.52O22 hexaferrite

We have presented a systematic study on structural, magnetic, and magnetodielectric (MD) properties of Y-type Ba2-xSrxMg2Fe11.48Mn0.52O22 (0 < x ≤ 1) hexaferrite. The temperature-dependent DC magnetization results exhibit Sr substitution enhances spin ordering transition temperature TI (TII) from 52 K (210 K) to 73 K (315 K). AC magnetic characterization suggests the presence of single cluster-glass transition (Tf1) at 45 K for x = 0.25. Interestingly, for higher Sr substitution x > 0.25, double cluster class transition is observed. The freezing temperature Tf1 decreases with an increase in x, while Tf2 increases substantially with x. The saturation magnetization (Ms) value is found to be decreased from 28.88 emu/g for x = 0.25 to 26.28 emu/g for x = 0.75 at 300 K. However, for x > 0.75 this value increases. Raman modes at 78, 135, 335, and 694 cm−1 show a gradual increase in Raman shift up to x = 0.75, but a drastic decrease is seen for x > 0.75. Along with enhanced magnetic properties, Sr doped sample shows better MD properties. The MD% value at RT increases with doping concentration up to x = 0.75 (MD% ∼1.2); beyond that, its value decreases. The maximum value of frequency-independent MD% and magnetoloss ML% of the BSMFM25 is found to be ∼3.5 and ∼0.2, respectively in the presence of a 1.3 T field at 100 Hz. The H-dependent MD exhibits symmetric anomalies close to the H-induced transition indicating an exchange-striction phenomenon in the samples.

Spin–phonon interaction and magnetoelastic coupling associated with unusual cluster-glass states in YFe0.9Cr0.1O3

The magnetic, optical phonon behavior of the polycrystalline YFe0.9Cr0.1O3 (YFC-10), prepared by solid-state reaction route, had been studied via static and ac magnetization measurements and Raman spectroscopic techniques respectively. The results indicated that YFe0.9Cr0.1O3 undergoes unusual cluster-glass transitions at low temperatures viz. Tf1 (SG1) = 108 K (Freez.1) and Tf2 (SG2) = 30 K (Freez.2) coexisting with the long-range weak ferromagnetic (WFM) state. Raman spectroscopic (RS) measurements revealed 12 distinct modes of vibrations at all temperatures with 83–433 K. Interestingly, the freezing transition at Tf1 is found to be accompanied by significant phonon renormalization. From the detailed analysis of the line-shape function of the Raman modes, the anomalous T-variation of the peak position and the linewidths suggests the existence of spin-phonon interaction in the present solid solution. Moreover the temperature dependent synchrotron X-ray diffraction studies between 10 and 300 K revealed the anomalous thermal variation of the lattice parameters and microscopic structural parameters such as super-exchange angles and (Fe/Cr)O6 octahedral bond lengths and bond angles at both the freezing transitions. Overall, the system exhibits the strong magnetoelastic and spin phonon coupling over a broad thermal regime viz. from Liquid. N2 to temperatures above room temperature (RT = 300 K) which makes YFe0.9Cr0.1O3 reliable for application purpose.

Transported properties and low-temperature magnetic behaviors of Ti x Cr1− x O2 films

Electronic transport and magnetic properties of Ti x Cr1−x O2 epitaxial films with low Ti concentrations have been studied. Compared with pure CrO2 film, Ti-doped films exhibit a significant increase of resistivity and the magnetoresistance at low temperature is more difficult to saturate even under an external field of 5 Tesla. The DC magnetization and AC susceptibility measurements suggest that a cluster glass freezing behavior occurs at low temperature in Ti-doped films. After analyzing the AC susceptibility using dynamic scaling theory, we have obtained the cluster-glass transition temperature T G = 97.8 K, the dynamic exponent zv = 12.37, and the characteristic timescale τ 0 = 10−16, which lies in the range of conventional cluster glass systems.

Investigation of magnetic order in a new intermetallic compound Nd2PtGe3

In the present study we report a successful synthesis of the new intermetallic compound Nd2PtGe3 by an arc-melting method. The powder X-ray diffraction analysis indicates that this compound crystallizes in an disordered variant of the AlB2-type structure (space group P6/mmm, no. 191) with lattice parameters a = 4.2455 Å and c = 4. 1933 Å. The compound exhibits a cluster-glass transition below Tf = 2.9 K, characterized through ac and dc magnetic susceptibility and heat capacity measurements.

Understanding the relationship between the local crystal structure and the ferrimagnetic ordering of CoxMn3-xO4 (x = 0–0.5) solid solutions

The local crystal structure alterations in the tetrahedral positions of the hausmannite Mn3O4 structure by Co2+ ions and its consequence on the magnetic ordering are studied in detail. The cation composition, bond distance and bond angle of the CoxMn3-xO4 series (x = 0.0. 0.1, 0.3 and 0.5) is determined by XRD Rietveld refinement. The charge state of the elements Co, Mn and O are investigated using XPS measurements, which confirm the bivalent cobalt ion occupation in the tetrahedral lattice. Considerable reduction in tetrahedral and axial octahedral bonds with the introduction of Co2+ ions dramatically increased the Curie temperature (TC) from 43 K (Mn3O4) to 62 K (Co0.5Mn2.5O4). The Lotgering-Srinivasan-Seehra model is employed to study the canted spin arrangement and the exchange interactions of Co0.5Mn2.5O4. The presence of cluster glass transition at TP = 42 K in Co0.3Mn2.7O4 is well-established through the AC susceptibility measurements and it is further substantiated by Vogel-Fulcher law and dynamic scaling power law. The origin of the cluster glass state is confirmed by the calculated strong geometric frustration factor (f = 19.5), due to the inhomogeneous distribution of cobalt ions in the intermediate concentrations. Field cooled isothermal magnetic measurements corroborated the exchange bias phenomenon in the Co0.3Mn2.7O4 sample, because of the interaction between ferrimagnetic-cluster glass phases occurring below the spin freezing temperature TP.

Cluster glass transition in the ternary Dy2AgIn3 system determined by neutron diffraction and Ac–Dc magnetization measurements

The crystallographic and magnetic properties of the polycrystalline intermetallic compound Dy2AgIn3 are presented. The compound crystallizes in the hexagonal CaIn2- type structure (space groupP63/mmc). The magnetic susceptibility data reveals a Curie–Weiss (CW) law behavior above120K, with a calculated effective magnetic moment μeff=10.63±0.29μB/Dy3+and a Curie paramagnetic temperatureθp=17.5K±0.5K, demonstrating the dominance of ferromagnetic (FM) couplings in the sample. In the temperature range of 60-120Kit exhibits a Griffith’s phase like behavior. The dc field cooled (FC) and zero field cooled (ZFC) susceptibility, show field dependent irreversible phenomena belowTr~43K, and the ZFC plots present a cusp glass like maxima at31K. The irreversibility temperatureTradopts aH2/3, field dependence of de Almeida–Thouless type line which defines the stability limits in the H-T plane withTr(0)=44.5±0.5K. The ac susceptibility data shows a relative shift in freezing temperature δTf~0.048±0.004, while near the freezing temperature it exhibits a Power- Vogel-Fulcher law dependency characterized by the dynamic exponentszν=7.4, single flip time τ0=10-6sandTg=24.5±0.65K. These values suggest the formation of cluster spin-glass states (CSG). At low angles the neutron diffraction (ND) profiles display diffuse scattering of antiferromagnetic (AFM) origin which is triggered by the ~5nm- magnetic spin clusters.

Magnetic and electrical properties of LuFe2O4 epitaxial thin films with a self-assembled interface structure

Thin film of LuFe2O4, one of multiferroics, deposited on an yttria-stabilized zirconia substrate shows a unique interface structure, leading to an exchange bias effect. The thin film itself undergoes spin glass or cluster glass transition.

Field induced nature and nonlinear DC susceptibility studies of Ni substituted Dy5Pd2 cluster glass system

We report a systematic investigation of the magnetic properties of Ni substituted Dy5Pd2 cluster glass system. Magnetic susceptibility result shows that both the compounds undergo paramagnetic to cluster glass transition. Remarkably, below this transition, they exhibit an additional field induced magnetic phase transition. This field induced nature of the magnetic phase transition is also clearly visible in the applied field response of magnetization and isothermal magnetic entropy change. Additionally, the cluster glass magnetic state is also analyzed by the temperature dependent magnetization memory effect and nonlinear DC susceptibility studies. Both the studies have confirmed the presence of two glassy transitions in these intermetallic compounds.

Experimental Evidence for a Cluster Glass Transition in Concentrated Lysozyme Solutions.

Lysozyme is known to form equilibrium clusters at pH ≈ 7.8 and at low ionic strength as a result of a mixed potential. While this cluster formation and the related dynamic and static structure factors have been extensively investigated, its consequences on the macroscopic dynamic behavior expressed by the zero shear viscosity η0 remain controversial. Here we present results from a systematic investigation of η0 using two complementary passive microrheology techniques, dynamic light scattering based tracer microrheology, and multiple particle tracking using confocal microscopy. The combination of these techniques with a simple but effective evaporation approach allows for reaching concentrations close to and above the arrest transition in a controlled and gentle way. We find a strong increase of η0 with increasing volume fraction ϕ with an apparent divergence at ϕ ≈ 0.35, and unambiguously demonstrate that this is due to the existence of an arrest transition where a cluster glass forms. These findings demonstrate the power of tracer microrheology to investigate complex fluids, where weak temporary bonds and limited sample volumes make measurements with classical rheology challenging.

Effect of the paramagnetic to spin-glass phase transition on the fundamental absorption edge of MnIn2Se4 magnetic semiconducting compound

The temperature dependence of the indirect and direct fundamental band gaps of the layered compound MnIn2Se4,that crystallizes in a rhombohedral defect structure with space group R -3m (D5/3d), was studied by optical absorption spectra. The data were analyzedin terms of current theoretical models that take into account the contribution of antiferromagnetic exchange interaction between spins to the shift of the energy gap EG with T in the vicinity of the critical paramagnetic to spin-glass phase transition. It was established that short- and long-range effect spin correlations dominate the contribution to this shift in the critical region below about 20 K, near the spin-glass freezing temperature Tf, and noncritical one, between about 70 and 160 K, far from Tf, respectively. An intermediate temperature region, compatible with the behaviour expected for a cluster-glass transition where a gradual freezing of the magnetic moments occurs, was also observed.

Ba9V3Se15: a novel compound with spin chains

In this work, a novel compound Ba9V3Se15 with one-dimensional (1D) spin chains was synthesized under high-pressure and high-temperature conditions. It was systematically characterized via structural, magnetic, thermodynamic and transport measurements. Ba9V3Se15 crystallizes into a hexagonal structure with a space group of P-6c2 (188) and the lattice constants of a = b = 9.5745(7) Å and c = 18.7814(4) Å. The crystal structure consists of face-sharing octahedral VSe6 chains along c axis, which are trimeric and arranged in a triangular lattice in ab-plane. Ba9V3Se15 is a semiconductor and undergoes complex magnetic transitions. In the zero-field-cooled (ZFC) process with magnetic field of 10 Oe, Ba9V3Se15 sequentially undergoes ferrimagnetic and spin cluster glass transition at 2.5 K and 3.3 K, respectively. When the magnetic field exceeds 50 Oe, only the ferrimagnetic transition can be observed. Above the transition temperature, the specific heat contains a significant magnetic contribution that is proportional to T1/2. The calculation suggests that the nearest neighbor (NN) intra-chain antiferromagnetic exchange J1 is much larger than the next nearest neighbor (NNN) intra-chain ferromagnetic exchange J2. Therefore, Ba9V3Se15 can be regarded as an effective ferromagnetic chains with effective spin-1/2 by the formation of the V(2)(↓)V(1)(↑)V(2)(↓) cluster.

Influence of magnetic frustration and structural disorder on magnetocaloric effect and magneto-transport properties in La1.5Ca0.5CoMnO6 double perovskite

The rare existence of a magnetocaloric effect, a Griffith phase, and frustrated magnetism in the antisite disorder compound La1.5Ca0.5CoMnO6 have been investigated in detail in this work. The nature of the observed Griffith phase (at TG ∼ 226 K) can be best understood in terms of ferromagnetic (FM) entities within the globally paramagnetic network above the Curie temperature. From the isothermal magnetization measurement around Curie temperature (TC ∼ 157 K) and cluster glass transition temperature (Tg ∼ 51 K), we have determined the maximum entropy change (−ΔSM) as ∼2.2 J/kg K and ∼1.2 J/kg K, respectively, for a magnetic field variation of 7 T. Interestingly, a sudden drop of resistivity curve at Tg, associated with magnetic frustration or magnetic disorder, can be related to the ferromagnetic (FM) phases with antiferromagnetic antiphase boundaries, giving rise to a large negative magnetoresistance (∼67%) at 45 K.

Ferromagnetic cluster glass behavior and large magnetocaloric effect in Ho2PtSi3

Magnetic properties and magnetocaloric effect of Ho2PtSi3, a new ternary intermetallic compound with the orthorhombic Ba2LiSi3-type structure, are studied by dc magnetization, ac susceptibility, magnetic relaxation, specific heat, and magnetic memory effect measurements. The experimental results indicate that this system undergoes a magnetic phase transition from a paramagnetic state to a ferromagnetic cluster state at a temperature TC ~ 6.5K followed by a cluster glass transition at Tf ~ 5.8K. The typical cluster glass features observed below Tf for Ho2PtSi3 include (1) broad peak in specific heat curve, (2) frequency dependent cusp in ac susceptibility curve, (3) evident irreversible magnetism, (4) long-time magnetic relaxation behavior, and (5) zero-field-cooling magnetic memory effect. On the other hand, the large values of magnetic entropy change, relative cooling power and adiabatic temperature change are estimated near TC under a field change. These results suggest that Ho2PtSi3 can be classified as a huge ferromagnetic cluster glass system with large magnetocaloric effect.

Cluster Glass Transition of Ultrasoft-Potential Fluids at High Density.

Using molecular dynamics simulation, we investigate the slow dynamics of a supercooled binary mixture of soft particles interacting with a generalized Hertzian potential. At low density, it displays typical slow dynamics near its glass transition temperature. At higher densities, particles bond together, forming clusters, and the clusters undergo the glass transition. The number of particles in a cluster increases one by one as the density increases. We demonstrate that there exist multiple cluster-glass phases characterized by a different number of particles per cluster, each of which is separated by distinct minima. Surprisingly, a so-called higher order singularity of the mode-coupling theory signaled by a logarithmic relaxation is observed in the vicinity of the boundaries between monomer and cluster glass phases. The system also exhibits rich and anomalous dynamics in the cluster glass phases, such as the decoupling of the self- and collective dynamics.

Effect of grain size on charge and spin correlations in Bi0.5Ca0.5MnO3 manganite nanoparticles

In this work we report the electron spin resonance (ESR) and magnetization (M) studies to understand the effect of grain size (GS) on the charge ordering and spin correlations in Bi0.5Ca0.5MnO3 manganite synthesized by sol–gel method. The suppression of charge ordering (CO), long-range antiferromagnetic (AFM) state, shifting of ferromagnetic (FM)-cluster glass (CG) transition towards higher temperatures and evolution of different magnetic correlations with decrease in GS are discussed in view of the changes in surface to volume ratio of nano-grains.