Cluster Glass Research Articles

Nonsaturating magnetoresistance, anomalous Hall effect, and magnetic quantum oscillations in the ferromagnetic semimetal PrAlSi

We report a comprehensive investigation of the structural, magnetic, transport and thermodynamic properties of a single crystal PrAlSi, in comparison to its nonmagnetic analogue LaAlSi. PrAlSi exhibits a ferromagnetic transition at $T_C$ = 17.8 K which, however, is followed by two weak phase transitions at lower temperatures. Based on the combined dc and ac magnetic susceptibility measurements, we propose the two reentrant magnetic phases below $T_C$ to be spin glasses or ferromagnetic cluster glasses. When the magnetic glassy states are suppressed by small field, several remarkable features appear. These include a linear, nonsaturating magnetoresistance as a function of field that is reminiscent of a topological or charge-compensated semimetal, and a large anomalous Hall conductivity amounting to $\sim$2000 $\Omega ^{-1}$cm$^{-1}$. Specific-heat measurements indicate a non-Kramers doublet ground state and a relatively low crystal electric field splitting of the Pr$^{3+}$ multiplets of less than 100 K. Shubnikov-de Hass oscillations are absent in LaAlSi, whereas they are clearly observed below about 25 K in PrAlSi, with an unusual temperature dependence of the dominating oscillation frequency $F$. It increases from $F$ = 18 T at 25 K to $F$ = 33 T at 2 K, hinting at an emerging Fermi pocket upon cooling into the ordered phase. These results suggest that PrAlSi is a new system where a small Fermi pocket of likely relativistic fermions is strongly coupled to magnetism. Whether hybridization between $f$ and conduction band is also involved remains an intriguing open problem.

Roles of Re-entrant cluster glass state and spin–lattice coupling in magneto–dielectric behavior of giant dielectric double perovskite La1.8Pr0.2CoFeO6

La based Co–Fe combined double perovskite (La1.8Pr0.2CoFeO6) was synthesized and the dielectric (zero-field and in-field), magnetic, x-ray absorption and Raman spectroscopy measurements have been investigated for La1.8Pr0.2CoFeO6 double perovskite. The existence of re-entrant cluster glass state is observed. The magneto–dielectric (MD) is found in two temperature regions (25–80 K and 125–275 K). It has been demonstrated that the observed MD at low and high temperatures are respectively due to the spin freezing and the spin–lattice coupling. Furthermore, the very large dielectric constant and the low loss suggest that La1.8Pr0.2CoFeO6 is very important from the application point of view.

Effect of R substitution in spin glass RFeTi2O7 compounds

Zirconolite oxides R3+Fe3+Ti2O7 (R rare earth element) are known to exhibit spin glass behaviour at low temperatures. Here we present a detailed study of these compounds for R = Eu, Gd, Dy, Ho, and Er, together with reviewed previous measurements on Sm, Tb, Tm, Yb and Lu, with the scope of determining the role played by the rare earth on their magnetic properties. They have been investigated using X-ray powder diffraction, and further characterized by magnetization, frequency dependent ac susceptibility and heat capacity measurements. RFeTi2O7 compounds are all isostructural showing orthorhombic structure, space group Pcnb at 300 K. Disorder of the magnetic ions in the RFeTi2O7 lattice induces spin glass behaviour at low temperatures, mainly due to the Fe sublattice. We show that magnetic rare earth ions participate in the spin glass state tuning its properties. The single ion anisotropy of the R3+ ions, excluding exchange interaction with other magnetic ions, has been calculated by ab initio methods, and expressed in terms of the g tensor of the ground doublet or quasi-doublet in Kramers (Sm, Dy, Er, Yb) and non-Kramers (Tb, Ho) ions, respectively, in an effective spin S* = 1/2 model. In the case of R with a singlet ground state (Eu, Tm) or a multiplet state (Gd), the ion is isotropic. We show that the relative increase in the spin-glass temperature ΔTSGR/TSGFe with respect to the LuFeTi2O7, where Lu is non-magnetic, correlates qualitatively with the product of the ratio gz/gJ (R = Tb, Dy, Ho, and Er), or g⊥/gJ (R = Sm), times the ratio of exchange interactions J~R,FeJFe,Fe determined from the paramagnetic room temperature susceptibility measurements. Besides, for increasing anisotropy the spin glass transition dynamics slows down to values typical of cluster glass. The coercive field below the transition is increased in the same trend. This paper explains the effect of the R-Fe exchange interaction and R single ion anisotropy on the spin-glass behaviour of these compounds.

Effect of substrate orientation on formation of cluster glass state in epitaxial LaMnO3 thin films

Cluster glass state, which is closely related to some special physical phenomena, has attracted extensive attention. Herein, we report a new phenomenon that is the substrate orientation can influence the formation of the cluster glass state in LaMnO3 (LMO) films. To explore the effect of substrate orientation on the formation of cluster glass state, the LMO thin films are epitaxially grown on (001)-, (110)- and (111)-oriented LaAlO3 (LAO) single crystal substrates by pulsed laser deposition (PLD), and the cluster glass state in which is investigated. The results show that the substrate orientation has a great influence on the formation of cluster glass state in the LMO epitaxial films. The LMO thin film grown on (001)-oriented LAO substrates is more likely to form cluster glass state than those grown on (110)- and (111)-oriented LAO substrates. This can be attributed to the different degrees of the ferromagnetic and antiferromagnetic interactions, which is caused by the different crystalline orientations and strain states of the epitaxial LMO thin films.

Sharp steps in magnetization, magnetoresistance, and magnetostriction in Pr0.6Sr0.4Co1−yGayO3

We report the magnetization, magnetoresistance, and magnetostriction in polycrystalline Pr0.6Sr0.4Co1−yGayO3 (y = 0.0–0.3) samples. Upon substitution of the non-magnetic Ga3+ cation for Co3+, the low temperature ground state transforms from a ferromagnetic metal for y = 0 to a cluster glass type semiconductor for y ≥ 0.2. The field-dependent magnetization, magnetoresistance, and magnetostriction for y ≥ 0.2 show reversible abrupt steps for both positive and negative magnetic fields at T ≤ 3 K, whereas all these quantities vary smoothly with the magnetic field above 4 K. Such steps in all three distinct physical quantities were never reported earlier in perovskite cobaltites, and they differ from observations made in manganites and intermetallic alloys. It is suggested that field-induced avalanche flipping of ferromagnetic clusters is the origin of observed steps in all these three quantities.

Shear-Induced Stack Orientation and Breakup in Cluster Glasses of Ring Polymers

Cluster glass-phase ring suspensions exposed to weak shear stress exhibit a stable reorientation of stacks as well as of individual ring polymers with the flow direction and into the flow-vorticity...

Modification of magnetic ground state in Tb[formula omitted]Ni0.90Si2.94 by thermal annealing

In this work, we have investigated the thermal annealing effect on the physical properties of an AlB2-type ternary intermetallic compound, Tb2Ni0.90Si2.94, that undergoes spin freezing behaviour coexisting with spatially limited antiferromagnetic phase below 9.9 K in as-cast form. Thermal annealing effect is found to result in considerable changes in the magnetic ground state properties of the system. Though only one magnetic transition around 9.9 K is observed for as-cast compound, the annealed sample exhibits two distinct magnetic transitions; one around TN∼ 13.5 K and another around Tf∼ 4 K. The magnetization measurements and zero field neutron diffraction study reveal that the high temperature transition is antiferromagnetic type, though of limited correlation length, while the low temperature transition corresponds to spin freezing behaviour. The ac susceptibility and heat capacity studies also confirm the existence of frustrated cluster glass state at lower temperature than the antiferromagnetic ordering temperature. Additionally, ac susceptibility data exhibits signature of an additional peak in the even lower temperature region (at 2.2 K for zero frequency) that tends to shift in opposite direction with frequency in contrast to that observed for conventional glassy transitions. The change in intrinsic local structural disorder of Ni and Si ions associated with annealing has been argued to be responsible for the different magnetic behaviour in as-cast and annealed samples.

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.

Observations of ferromagnetic cluster glass and exchange bias behavior in the double perovskite compound La2Cu0.9Cr0.1IrO6

La2CuIrO6 is a spin–orbit coupled Mott insulator, and shows a transition to noncollinear antiferromagnetic state from paramagnetic state below 74 K, and further into a weak ferromagnetic state below 54 K. Despite having two different magnetic phases, the La2CuIrO6 compound does not exhibit exchange bias phenomenon. In this present work, we report an experimental investigation on the structural and magnetic properties of the double perovskite compound La2Cu0.9Cr0.1IrO6 through high-resolution synchrotron x-ray diffraction, x-ray absorption near edge structure (XANES), and temperature and field-dependent magnetization measurements. Powder x-ray diffraction analysis reveals that the sample crystallizes in triclinic structure (space group P) alike parent La2CuIrO6 compound, while XANES measurements rule out the possibility of valence state alteration between constituting elements in this sample. Interestingly, La2Cu0.9Cr0.1IrO6 compound is found to exhibit ferromagnetic cluster glass behavior, where field-cooled magnetization undergoes two ferromagnetic transitions. A significant enhancement of ferromagnetic component is also evident from hysteresis loop study, which is likely associated with the electron hopping between Jeff = 1/2 pseudospin state of Ir4+ ions and empty eg-orbital of Cr3+ ions. Exclusively, this Cr-doped compound exhibits exchange bias effect, which is related to the complex interfacial exchange coupling between the ferromagnetic clusters and the host antiferromagnetic matrix.

Probing the Griffiths like phase, unconventional dual glassy states, giant exchange bias effects and its correlation with its electronic structure in Pr2−xSrxCoMnO6

Crystal, electronic structure, dc and ac magnetization properties of the hole substituted (Sr2+) and partially B-site disordered double perovskite Pr2−xSrxCoMnO6 system have been investigated. The XRD pattern analysis showed a systematic decrease in the lattice parameters owing to the enhanced oxidation states of the Co/Mn ions. The electronic structure study by XPS measurements suggested the presence of mixed valence states of the B-site ions (Co2+ /Co3+ and Mn3+ /Mn4+) with significant enhancement of the average oxidation states due to hole doping. The mere absence of electronic states near the Fermi level in the valence band (VB) spectra for both pure (x = 0.0) and Sr doped (x = 0.5) systems indicated the insulating nature of the samples. Sr substitution is observed to increase the spectral weight near the Fermi level suggesting for an enhanced conductivity of the hole doped system. The dc magnetization data divulged a Griffiths like phase above the long-range ordering temperature. A typical re-entrant spin glass like phase driven by the inherent anti-site disorder (ASD) has been recognized by ac susceptibility study for both the pure and doped systems. Most interestingly, the emergence of a new cluster glass like phase (immediately below the magnetic ordering temperature and above the spin-glass transition temperature) solely driven by the Sr substitution has been unravelled by ac magnetization dynamics study. Observation of these dual glassy states in a single system is scarce and hence placed the present system amongst the rare materials. The isothermal magnetization measurements further probed the exhibition of the giant exchange bias effect originated from the interfacial exchange interactions due to existence of low temperature antiferromagnetic clusters embedded in the glassy matrix.

High temperature spin cluster glass behavior in Co- and Si-substituted garnet ferrite thin films

In this study, lutetium iron garnet (Lu3Fe5O12; LuIG) thin films have been grown on Y3Al5O12 (1 1 1) substrates by a pulsed laser deposition and are co-substituted with strong magnetically anisotropic ions of Co2+ and nonmagnetic ones of Si4+. LuIG is a garnet-structured ferrimagnet with an exceptionally low Gilbert damping constant as 10−5. The substitution of Co2+ and Si4+ induces a chemical disorder and competing antiferromagnetic and ferromagnetic interactions, which induce a spin glass behavior. When the Co–Si substitution ratio is increased, a spin-freezing behavior is observed below the spin-freezing temperature TG = 190–220 K of the Lu3Fe4Co0.5Si0.5O12 film; this indicates the presence of a cluster glass phase. The film demonstrates a characteristic memory effects in the temperature range 120–180 K, which are below TG; this reveals the presence of a metastable magnetic state in the multi-valley energy landscape with shallow activation energy barriers. Ferromagnetic resonance measurements confirm increased perpendicular anisotropy energy induced by Co substitution and spin-wave characteristics including the inverse spin Hall effect voltage (VISHE). Lu3Fe5-2xCoxSixO12 films show an increase in damping and a decrease in VISHE at the cryogenic temperature, which are attributed to the impurity relaxation mechanism. Therefore, the Co- and Si-substituted films exhibit strong spin-wave damping at a low temperature, which reflects the spin-freezing dynamics of cluster glass behaviors.

Cluster Glass Behavior in Orthorhombic SmFeO3 Perovskite: Interplay between Spin Ordering and Lattice Dynamics

In this report, the isothermal time-dependent Raman scattering study has been used to investigate the origin of the cluster glass state in samarium orthoferrites (SmFeO3) via probing selective dyna...

Cluster prevalence in concentrated ring-chain mixtures under shear.

Semiflexible ring polymers are known to exhibit clustering behavior and form stacks in concentrated solutions. Recently, weak shear was suggested to re-orient these stacks with flow, a phenomenon more easily visible in more concentrated solutions [Liebetreu et al., ACS Appl. Polym. Mater., 2020, 2(8), 3505-3517, DOI: 10.1021/acsapm.0c00522]. In this work, we investigate the impact of mixing linear chains and rings in a similar system under shear, studying clustering in the presence of semiflexible, rod-like chains. We present a correlation between chain monomer fraction and clustering behavior as linear chains take up less space, thus decreasing the system's effective density and, subsequently, clustering. However, we suggest mixtures with a low chain concentration to maintain or potentially enhance clustering at equilibrium while this effect is destroyed under shear. The mixing of chains and rings may therefore be used to create more strongly organized structures susceptible to reorientation via weak shear.

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.

Cluster glass behavior of the frustrated birnessites AxMnO2·yH2O(A=Na,K)

We report on the synthesis and magnetic properties of frustrated Na0.22MnO2*0.39H2O and K0.6MnO2*0.48H2O with the birnessite structure. The structure, static and dynamic magnetic properties of the compounds are investigated in detail. A combination of DC and AC magnetic susceptibility measurements and magnetization decay measurements reveal cluster glass behavior below the freezing temperature of 4 K for Na-birnessite and 6 K for K-birnessite. The frequency dependence of the freezing temperature is analyzed on the basis of dynamic scaling laws including the critical slowing down formula and the Vogel-Fulcher law, which further confirm cluster glass formation in both compounds.

Relaxor ferroelectrics and related superglasses

Mesoscopic ferroic glasses such as martensitic strain glass Ti50−x Ni50+x, magnetic cluster glass La0.7Ca0.3Mn0.7Cd0.3O3, and superdipolar relaxor PbMg1/3Nb2/3O3 (PMN) undergo glass transitions preceded by mesoscopic precursor patterns – elastic or magnetic tweed or polar nanoregions (PNR), respectively. In PMN the PNR glass transition at Tg ≈ 240 K reveals glassy dynamic criticality and non-ergodicity of the field-induced low-T phase similar to that of a superspin glass of fixed magnetic nanoparticles in a diamagnetic environment. A final ferroelectric domain state is reached at Tp ≈ 213 K via PNR percolation, which is absent in weak relaxors like BaTi0.65 Zr0.35O3 (BTZ35).

Spin-lattice coupling and exchange bias in perovskite La0.64Sr0.36FeO3−δ

We report studies of perovskite La0.64Sr0.36FeO3−δ ceramics through measurements of magnetization and mechanical spectroscopy. We find an unusual magnetic anomaly around 225 K, R3¯c↔Pnma octahedral tilting transition where a step-like change of magnetization was observed. The step-like change depends on the external magnetic field. The magnetic anomaly indicates a change of the magnetocrystalline anisotropy axis and it suggests a substantial role of spin-lattice coupling in La0.64Sr0.36FeO3−δ. Below the tilting transition, a broad peak in zero-field-cooling dc magnetization was observed around TP = 125 K and exchange bias was observed below TP. The exchange bias field shows a strong dependence on temperature and cooling field. It suggests that the exchange bias is resulting from the coupling at cluster glass or ferromagnetic and antiferromagnetic interface where ferromagnetic and antiferromagnetic domains coexist below TP in La0.64Sr0.36FeO3−δ.

Exotic magnetic behaviour and evidence of cluster glass and Griffiths like phase in Heusler alloys Fe2-xMnxCrAl (0\u2009\u2264\u2009x\u2009\u2264\u20091)

We present a detailed study of structural, magnetic and thermodynamic properties of a series of Heusler alloys Fe2-xMnxCrAl (x = 0, 0.25, 0.5, 0.75 and 1). Structural investigation of this series is carried out using high resolution synchrotron X-ray diffraction. Results suggest that with increasing Mn concentration, the L21 structure of Fe2CrAl is destabilized. The DC magnetization results show a decrement in paramagnetic (PM) to ferromagnetic (FM) phase transition temperature (TC) with increasing Mn concentration. From the systematic analysis of magnetic memory effect, heat capacity, time dependent magnetization, and DC field dependent AC susceptibility studies it is observed that, Fe2CrAl exhibits cluster glass(CG)-like transition approximately at 3.9 K (Tf2). The alloys, Fe1.75Mn0.25CrAl and Fe1.5Mn0.5CrAl exhibit double CG-like transitions near Tf1 ~ 22 K, Tf2 ~ 4.2 K and Tf1 ~ 30.4 K, Tf2 ~ 9.5 K respectively, however, in Fe1.25Mn0.75CrAl, a single CG-like transition is noted at Tf2 ~ 11.5 K below TC. Interestingly, FeMnCrAl shows the absence of long ranged magnetic ordering and this alloy undergoes three CG-like transitions at ~22 K (Tf*), 16.6 K (Tf1) and 11 K (Tf2). At high temperatures, a detailed analysis of temperature response of inverse DC susceptibility clearly reveals the observation of Griffiths phase (GP) above 300 K (T*) in Fe2CrAl and this phase persists with Mn concentration with a decrement in T*.

Mictomagnetic full-Heusler nanoprecipitates in (Ti, Zr, Hf)NiFexSn half-Heusler composites

One of the most recent strategies used to enhance the efficiency of certain thermoelectric (TE) materials relies on the interaction of magnetic dopants with charge carriers and lattice vibrations. Understanding the forms of magnetism inherent to the materials is critical for continued TE performance optimization. Accordingly, we herein analyze the low-temperature magnetic properties of a mictomagnetic composite system we previously engineered for improved TE power generation capabilities. The Ti0.25Zr0.25Hf0.50NiFexSn0.975Sb0.025 set of materials features long-range magnetic ordering as a result of an intentional magnetic full-Heusler secondary phase in the half-Heusler composites. Having the highest population density of magnetic nanoprecipitates, the x = 0.05 sample exhibits both superparamagnetic and cluster glass behavior, with blocking temperatures ranging from ≈ 100 to 250 K. We discern the phenomena from the sharp, open DC magnetization loops, the splitting of the zero-field-cooled and field-cooled DC moments, as well as the frequency- and field-dependent AC susceptibility measurement. In the magnetotransport data, we find evidence for the Kondo effect in these dilute magnetic semiconductors, in addition to weak antilocalization in the pure sample that is abated in the magnetic samples.

The effect of particle size on the structural, magnetic and electrical properties of La0.9Ba0.1MNO3 manganite samples

ABSTRACTIn this work, the magnetic and transport properties of micro and nanometer-sized samples of La0.9Ba0.1MnO3 manganite have been studied. The temperature variation of ac susceptibility of the nanometer-sized sample shows one transition at high temperature (265 K). On the contrary, the ac susceptibility of the micrometer-sized sample shows two transitions with a high-temperature transition occurring at 240 K and low-temperature transition around 100 K. The high-temperature transition corresponds to the paramagnetic-ferromagnetic (PM–FM) transition (Tc) and is independent of frequency, while the low-temperature transition is frequency-dependent and shifts toward high temperatures by increasing frequency. The different magnetic behavior for two samples may be understood on the basis of crystalline homogeneity. The competition between FM double exchange and antiferromagnetic superexchange component in the micrometer-sized sample leads to the cluster glass state at low temperatures. The magnetotransport data further supports the obtained results from magnetic measurements.