Spin Glass Materials Research Articles

Exploring the critical behavior of the anomalous spin-glass transition in Ga1−xMnxS

Single-crystalline Ga1−xMnxS is a quasi-two-dimensional system that exhibits an anomalous spin-glass transition temperature compared with the other well-known spin-glass systems. In contrast to the other known spin-glasses that all have three-dimensional structures, our host chalcogenide GaS system is quasi-two-dimensional. Recent interest in utilizing spin-glass materials for applications in short-term, low-energy memory and processing power make this new 2-D system important for further exploration. We report on the critical behavior of the anomalous spin-glass transition in a single-crystalline Ga0.91Mn0.09S system. Using the scaling equation of state describing the spin-glass transition in Ga1−xMnxS, we obtained the relation χnl = C1H2/δ and extract the value δ = 5.5 ± 0.5 for this critical exponent as well as a value of ϕ = 4.8 for another critical exponent. We find this value of delta for the critical temperature Tc = 11.2 K, combined with the other critical exponents γ = 4.0 and β = 0.8 form a self-consistent description of the spin-glass transition in this unusual 2-D spin-glass system. Interestingly, these results represent convincing evidence that, despite Ga1−xMnxS having a quasi-two-dimensional structure, Ga1−xMnxS undergoes a true spin-glass transition and is related to the class of semiconducting spin-glass materials with short-range interactions. The spin-glass transition in Ga1−xMnxS is characterized by critical exponents similar to the three-dimensional spin-glass systems.

Peratic phase transition by bulk-to-surface response

The study of dynamical phase transitions has been attracting considerable research efforts in the last decade. One theme of present interest is to search for exotic scenarios beyond the framework of equilibrium phase transitions. Here, we establish a duality between many-body dynamics and static Hamiltonian ground states for both classical and quantum systems. We construct frustration free Hamiltonians whose ground state phase transitions have rigorous duality to chaotic transitions in dynamical systems. By this duality, we show the corresponding ground state phase transitions are characterized by bulk-to-surface response, which are then dubbed "peratic" meaning defined by response to the boundary. For the classical system, we show how the time-like dimension emerges in the static ground states. For the quantum system, the ground state is a superposition of geometrical lines on a two dimensional array, which encode the dynamical Floquet evolution history of one dimensional disordered spin chains. Our prediction of peratic phase transition has direct consequences in quantum simulation platforms such as Rydberg atoms and superconducting qubits, as well as anisotropic spin glass materials. The discovery would shed light on the unification of dynamical phase transitions with equilibrium systems.

Tuning the spontaneous exchange bias effect with Ba to Sr partial substitution in La1.5(Sr0.5−xBax)CoMnO6

The spontaneous exchange bias (SEB) effect is a remarkable phenomenon recently observed in some reentrant spin-glass materials. Here, we investigate the SEB in La1.5(Sr0.5−xBax)CoMnO6 double-perovskites, a system with multifarious magnetic phases for which a notable increase in the exchange bias field is observed for intermediate Sr/Ba concentrations. The Ba to Sr substitution leads to the enhancement of the crystal lattice, which is accompanied by the increase in both the effective magnetic moment (μeff) and the antiferromagnetic (AFM) transition temperature that is observed below the ferromagnetic ordering. Such an increase is likely related to the increased fraction of Co3+ in the high spin configuration, leading to the enhancement of the Co3+–O–Mn4+ AFM phase and the reduction in the uncompensation of the AFM coupling between Co and Mn. The combined effect of the increased μeff and AFM phase plausibly explains the changes in the SEB effect.

Spin Symmetry Breaking: Superparamagnetic and Spin Glass-Like Behavior Observed in Rod-Like Liquid Crystalline Organic Compounds Contacting Nitroxide Radical Spins

Liquid crystalline (LC) organic radicals were expected to show a novel non-linear magnetic response to external magnetic and electric fields due to their coherent collective molecular motion. We have found that a series of chiral and achiral all-organic LC radicals having one or two five-membered cyclic nitroxide radical (PROXYL) units in the core position and, thereby, with a negative dielectric anisotropy exhibit spin glass (SG)-like superparamagnetic features, such as a magnetic hysteresis (referred to as ‘positive magneto-LC effect’), and thermal and impurity effects during a heating and cooling cycle in weak magnetic fields. Furthermore, for the first time, a nonlinear magneto-electric (ME) effect has been detected with respect to one of the LC radicals showing a ferroelectric (chiral Smectic C) phase. The mechanism of the positive magneto-LC effect is proposed and discussed by comparison of our experimental results with the well-known magnetic properties of SG materials and on the basis of the experimental results of a nonlinear ME effect. A recent theoretical study by means of molecular dynamic simulation and density functional theory calculations suggesting the high possibility of conservation of the memory of spin-spin interactions between magnetic moments owing to the ceaseless molecular contacts in the LC and isotropic states is briefly mentioned as well.

Spin pumping into a spin glass material

Spin pumping is a recently established means for generating a pure spin current, whereby spins are pumped from a magnet into the adjacent target material under the ferromagnetic resonance condition. We theoretically investigate the spin pumping from an insulating ferromagnet into spin glass materials. Combining a dynamic theory of spin glasses with the linear-response formulation of the spin pumping, we calculate temperature dependence of the spin pumping near the spin glass transition. The analysis predicts that a characteristic peak appears in the spin pumping signal, reflecting that the spin fluctuations slow down upon the onset of spin freezing.

Local magnetic cluster size identified by neutron total scattering in the site-diluted spin glass SnxFe4−xN (x=0.88)

A detailed structure analysis for the site-diluted $\mathrm{S}{\mathrm{n}}_{x}\mathrm{F}{\mathrm{e}}_{4\ensuremath{-}x}\mathrm{N}$ ($x=0.25$, 0.41, and 0.88) has been carried out through complex modeling of the neutron total scattering data. We present quantitative evidence showing the local ferromagnetic cluster size extending to \ensuremath{\sim}8 \AA{} on average when $\mathrm{S}{\mathrm{n}}_{0.88}\mathrm{F}{\mathrm{e}}_{3.12}\mathrm{N}$ undergoes the spin-glass transition (the other two not showing such a transition). The modeling methodology used in this work involving the corefinement of the nuclear and magnetic structure in both real and reciprocal space can potentially be applied generally to explore a variety of spin-glass material problems.

Consideration of analogies between magnetic and quantum notices for molecular network

Magnetic properties of spin glass materials [9,13] are close to quantum interpretation in their nature description [17]. Therefore, we can look for possible kinds of analogies in process of defining theoretic and practice conventions, rules and applications of the specific characteristics in elaboration quantum calculation strategies. We have not investigated possibilities to create directly quantum calculation units and practice calculation structures like qubits, registers, gates etc. [4,18], but dealing with spin and quantum definitions and descriptions we can try to involve these notices from different domains. Such a pragmatic approach only intuitively gives chances to create the transition theory and implement it even partially. Obviously, almost all of us have heard about quantum factorization, cryptography or teleportation but it is obtained as a result of exploration casually selected quantum properties and adapting them to mathematic problems. In our approach, we carefully investigate involutions among spin and quantum nature looking at possible implementation in molecular network.

Quasi-two-dimensional spin correlations in the triangular lattice bilayer spin glass LuCoGaO4

We present a single-crystal time-of-flight neutron scattering study of the static and dynamic spin correlations in ${\mathrm{LuCoGaO}}_{4}$, a quasi-two-dimensional dilute triangular lattice antiferromagnetic spin-glass material. This system is based on ${\mathrm{Co}}^{2+}$ ions that are randomly distributed on triangular bilayers within the ${\mathrm{YbFe}}_{2}{\mathrm{O}}_{4}$-type, hexagonal crystal structure. Antiferromagnetic short-range two-dimensional correlations at wave vectors $\mathbf{Q}=\left(1/3,1/3,L\right)$ develop within the bilayers at temperatures as high as $|{\mathrm{\ensuremath{\Theta}}}_{\mathrm{CW}}|\ensuremath{\sim}100$ K and extend over roughly five unit cells at temperatures below ${T}_{\mathrm{g}}=19$ K. These two-dimensional static correlations are observed as diffuse rods of neutron scattering intensity along ${c}^{*}$ and display a continuous spin freezing process in their energy dependence. Aside from exhibiting these typical spin-glass characteristics, this insulating material reveals a novel gapped magnetic resonant spin excitation at $\mathrm{\ensuremath{\Delta}}E\ensuremath{\sim}12\phantom{\rule{0.28em}{0ex}}\mathrm{meV}$ localized around $\mathbf{Q}=\left(1/3,1/3,L\right)$. The temperature dependence of the spin gap associated with this two-dimensional excitation correlates with the evolution of the static correlations into the spin-glass state ground state. We associate it with the effect of the staggered exchange field acting on the ${S}_{\mathrm{eff}}=1/2$ Ising-like doublet of the ${\mathrm{Co}}^{2+}$ moments.

Investigation of magnetic properties on spin-ordering effects of FeGa2S4 and FeIn2S4

We have studied crystal and magnetic properties of chalcogenides FeGa2S4 and FeIn2S4 with X-ray diffractometer (XRD), magnetic property measurement system (MPMS), magnetometer, physical property measurement system (PPMS), and Mössbauer spectrometer. The crystal structure has 2-dimension triangular lattice structure with P-3m1 of FeGa2S4, while FeIn2S4 has inverse spinel with space group Fd3m. The AC magnetic susceptibility measurements show that FeGa2S4 is an insulating spin glass material, exhibiting geometrical frustration, unlike in the antiferromagnetic [AFM] metallic spin glass FeIn2S4. From hysteresis (M-H) curves at 4.2K, FeGa2S4 has spin-flop behavior with an angle of 120° of triangle, as against linear slope of FeIn2S4 due to anti-parallel spin. The gap energy by splitting of 5T2g, Δ1 and electric quadrupole splitting ΔEQ of FeIn2S4 are much higher than that of FeGa2S4 at 4.2K because FeGa2S4 is geometrically frustrated magnet having degenerate ground state at low temperature.

Magnetic and magnetocaloric properties of spin-glass material DyNi0.67Si1.34

Structural, magnetic, and magnetocaloric properties of DyNi0.67Si1.34 were investigated using X-ray powder diffraction, magnetic susceptibility, and magnetization measurements. X-ray powder diffraction pattern shows that DyNi0.67Si1.34 crystallizes in the AlB2-type hexagonal structure (space group: P6/mmm, No. 191, a=b=3.9873(9)Å, and c=3.9733(1)Å). The compound is a spin-glass with the freezing temperature TG=6.2K. The ac magnetic susceptibility measurements confirm magnetic frustration in DyNi0.67Si1.34. The maximum value of the magnetic entropy change determined from M(H) data is −16.1J/kgK at 10.5K for a field change of 70kOe.

Ce2PtGe3: a new ordered orthorhombic superstructure in the AlB2family with spin glass behavior

A new compound Ce2PtGe3crystallizing in a new ordered superstructure of the AlB2type with an orthorhombicCmcespace group was found to be a spin glass material at low temperature.

Slow relaxation of resistance in nanostructured La<sub>0.83</sub>Sr<sub>0.17</sub>MnO<sub>3</sub> films induced by pulsed magnetic fields

The results of colossal magnetoresistance (MR) relaxation investigations in nanostructured and epitaxial La-Sr-Mn-O films grown by the MOCVD technique are presented. The films were studied in a pulsed magnetic field ranged from 2 to 10 T at the temperature of 80 K. The slow relaxation of resistance which takes place during milliseconds when the magnetic field is switched off is analysed using the Kohlrausch-Williams-Watts model. It was found that this relaxation is typical of spin-glass materials and is related with properties of disordered grain boundaries of nanostructured films. The MR relaxation of epitaxial films was not observed. The influence of film preparation conditions on MR relaxation was analysed in order to develop high pulsed magnetic field sensors exhibiting small dynamic “memory” effect and operating at low temperatures.

Spin dynamics in IrSr2Sm1.15Ce0.85Cu2O10: Complex magnetic behavior in a layered iridocuprate

A muon spin rotation (\ensuremath{\mu}SR), neutron, and synchrotron diffraction study of the reentrant spin-glass material IrSr${}_{2}$Sm${}_{1.15}$Ce${}_{0.85}$Cu${}_{2}$O${}_{10}$ is presented. The synthesis has been optimized, and Rietveld refinement of the diffraction patterns shows no sign of the previously reported Ir/Cu cation exchange but confirms the structure along with the disordered tilts and rotations of IrO${}_{6}$ octahedra. The zero-field-\ensuremath{\mu}SR response indicates a complex temperature dependence to the magnetism with multiple transitions that are confirmed to be bulk phenomena. Consecutive transitions are reported at ${t}_{1}$ $=$ 140, ${t}_{2}$ $=$ 20, and ${t}_{3}$ $=$ 6 K. The broad transition at 140 K is assigned to antiferromagnetic ordering of Ir${}^{4+}$ spins with a stripe spin structure. The low-temperature transitions are a result of antiferromagnetic ordering of Cu${}^{2+}$ spins followed by the freezing of a disordered Ir spin component, further evidenced by a strong damping of the oscillation amplitude below 6 K. These observations confirm the bulk nature of the previously reported reentrant spin-glass behavior of this complex magnetic system.

Field-pulse memory in a spin-glass

We report a magnetic field-pulse memory effect in the temperature-dependent magnetization of Tb30Ru6.0Sn29.5, a spin-glass material having a newly identified structure type. Tb30Ru6.0Sn29.5 exhibits a glassy magnetization component of ∼2290 emu/mol-Tb, which represents over 84% of its total saturation magnetization. We show that when a magnetic field pulse of a few hundred gauss is applied to the sample as it is cooling, the system retains a memory of the temperature at which the pulse was applied. Upon warming, the imprinted memory is observed as a precipitous drop in magnetization at the pulse temperature.

Oxygen miscibility gap and spin glass formation in the pyrochlore Lu2Mo2O7

Abstract Rare earth ( R ) molybdate pyrochlores, R 2 Mo 2 O 7 , are of interest as frustrated magnets. Polycrystalline samples of Lu 2 Mo 2 O 7− x prepared at 1600 °C display a coexistence of cubic pyrochlore phases. Rietveld fits to powder neutron diffraction data and chemical analyses show that the miscibility gap is between a stoichiometric x =0 and an oxygen-deficient x ≈0.4 phase. Lu 2 Mo 2 O 7 behaves as a spin glass material, with a divergence of field cooled and zero field cooled DC magnetic susceptibilities at a spin freezing temperature T f =16 K, that varies with frequency in AC measurements following a Vogel–Fulcher law. Lu 2 Mo 2 O 6.6 is more highly frustrated spin glass and has T f =20 K.

The Magnetic Behaviors of Spin-Glass $\hbox{FeGa}_{2}\hbox{O}_{4}$ System

We present the investigation of magnetic properties of spin-glass FeGa2O4 system. From X-ray diffraction patterns of FeGa2O4, refined with Rietveld's refinement method, its structure is determined to be cubic spinel with space group Fd - 3m and the lattice parameter of α0 = 8.385 Å. From temperature-dependent magnetization curves under 1000 Oe, the Neel temperature is found to be TN = 14 K, which coincides with the value obtained from the Mossbauer spectrum. The freezing temperature Tf of the sample shifts to higher temperature with increasing frequency, as seen in conventional metallic spin glasses. Also, we have determined the small activation energy, Ea of 1.04266 × 10-4 meV from Arrhenius law v = v0 exp(-En/kBTf), where kB is Boltzmann constant, and Ea is activation energy. The Mossbauer spectrum at 4.2 K shows severely distorted 8-line shape coming from frozen spin-disorder state and an incommensurate spin structure, as in spin glasses. The change in the electric quadrupole shift above Tf is caused by the presence of the maximum electric dipole interaction among frozen disordered spins around Tf as in spin-glass material, and charge re-distribution from spin-relocation arising above TN.

Unreachable glass transition in dilute dipolar magnet

In magnetic systems the combined effects of disorder and frustration may cause the moments to freeze into a disordered state at a spin-glass transition. Recent experiments have shown that the rare earth compound LiHo(0.045)Y(0.955)F(4) freezes, but that the transition is unreachable because of dynamics that are 10(7) times slower than in ordinary spin-glass materials. This conclusion refutes earlier investigations reporting a speed-up of the dynamics into an exotic anti-glass phase caused by entanglement of quantum dipoles. Here we present a theory, backed by numerical simulations, which describes the material in terms of classical dipoles governed by Glauber dynamics. The dipoles freeze and we find that the ultra-slow dynamics are caused by rare, strongly ordered clusters, which give rise to a previously predicted, but hitherto unobserved, Griffths phase between the paramagnetic and spin-glass phases. In addition, the hyperfine interaction creates a high energy barrier to flipping the electronic spin, resulting in a clear signature in the dynamic correlation function.

Evidence for spin-glass state in nonmagnetic atom disorder compound Pr2AgIn3

A systematic investigation of magnetic properties has been performed on intermetallic compound Pr2AgIn3, which crystallizes in a disordered hexagonal CaIn2-type structure. We present the experimental results of ac and dc susceptibility, magnetization, magnetic relaxation, specific heat and electrical resistivity measurements. The results provide clear evidence for the formation of spin-glass state in Pr2AgIn3 below a spin freezing temperature Tf∼3.7 K accompanied with a short-range magnetic order. The spin-glass behavior of Pr2AgIn2 is discussed and compared with that observed for the isostructural compounds Ce2AgIn3 and Nd2AgIn3 as well as other 2:1:3 spin-glass materials. The spin-glass state in Pr2AgIn3 can be considered to originate from the continued site randomness of the nonmagnetic elements, Ag and In, which introduce the random distribution of the RKKY interactions.

Critical phenomena of canonical spin glass systems with large Dzyaloshinsky–Moriya anisotropy

We have studied critical phenomena of spin glass transition for larger Dzyaloshinsky–Moriya anisotropy Heisenberg spin glass system, PtMn. The analysis of nonlinear magnetizations in the framework of the existence of a phase transition at Tg yields the critical exponents δ = 2.5 ± 0.3, γ = 1.5 ± 0.3 and β = 1 ± 0.3. These results suggest that the universality class of spin glass transition on PtMn is the same as those of CuMn, AgMn and AuFe systems. Experimentally, there is an indication of a unique universality class for Heisenberg spin glass materials.

Memory effect in Dy0.5Sr0.5MnO3 single crystals

We have performed a series of magnetic aging experiments on single crystals ofDy0.5Sr0.5MnO3. The results demonstrate striking memory and chaos-like effects in this insulating half-dopedperovskite manganite and suggest the existence of strong magnetic relaxation mechanismsof a clustered magnetic state. The spin-glass-like state established below a temperatureTsg≈ 34 K originates from quenched disorder arising due to the ionic-radii mismatch at the rareearth site. However, deviations from the typical behavior seen in canonical spin glassmaterials are observed which indicate that the glassy magnetic properties are due tocooperative and frustrated dynamics in a heterogeneous or clustered magnetic state. Inparticular, the microscopic spin flip time obtained from dynamical scaling near the spinglass freezing temperature is four orders of magnitude larger than microscopictimes found in atomic spin glasses. The magnetic viscosity deduced from the timedependence of the zero-field-cooled magnetization exhibits a peak at a temperatureT < Tsg and displays a marked dependence on waiting time in zero field.