Spin-glass Phenomena Research Articles

Influence of fabrication conditions on the structural characteristics and the magnetic properties of FeAl2O4

AbstractWe report a systematic evaluation of the magnetic properties of FeAl2O4 focusing on the relationship between the fabrication conditions and its structural characteristics, in order to improve ceramics processing in applications of this material. For this purpose, the most important factor to control is the inversion parameter, expressed as y in the (Fe1−yAly)(Al1−y/2Fey/2)2O4 composition, which is relatively high for the spinel aluminate of a transition metal. The magnetic properties of these samples all show the spin glass phenomenon at low temperatures, and the cusp temperature depends systematically on this y value. This means that the evaluation of these magnetic properties will be an effective way to predict some characteristics of product FeAl2O4. Additionally, this study found an anomaly in the structural and magnetic characteristics of FeAl2O4 fabricated at a low temperature. This is thought to originate in a tiny and a small amount of impurity. It will be key for discussing the quality of chemically synthesized FeAl2O4, which is typically produced at low temperatures.

Spin glass and exchange bias phenomena in NdSrNiMnO6 nanoparticles: Role of antiferromagnetic antisite disorders

We report the discovery of spin glass (SG) and exchange bias (EB) phenomena in NdSrNiMnO6 nanoparticles. Doping at Nd site in the double perovskite compound Nd2NiMnO6, induces antisite disorders leading to antiferromagnetic antiphase boundaries within the system, which are further responsible for the observed phenomena. The role of particle size on these effects has been discussed as the amount of antisite disorder may vary with particle size. We observed a high Curie temperature (TC ∼ 264 K) for small size samples. As the particle size increases, the ferromagnetic (FM) transition becomes indistinct and system transforms to a magnetically frustrated state containing co-existence of FM, antiferromagnetic (AFM) and SG phases. Meanwhile, TC decreases with increasing particle size and the FM ordering becomes unclear for largest particle size sample. The detail investigation of ac susceptibility, memory effect, DC magnetization and magnetic relaxation measurements exposes the SG behavior in the largest particle size sample. By varying the amount of antisite disorders in the NdSrNiMnO6 with increasing particle size, we obtained intrinsic EB effect with a large EB field (∼640 Oe). Further, the EB effect has also been explored by carrying out the cooling field dependent EB measurements in addition to training effect experiments. The exchange interaction between the AFM core and SG like shell of the system is explained through a phenomenological core shell model.

A rock-salt-type Li-based oxide, Li3Ni2RuO6, exhibiting a chaotic ferrimagnetism with cluster spin-glass dynamics and thermally frozen charge carriers.

The area of research to discover new Li containing materials and to understand their physical properties has been of constant interest due to applications potential for rechargeable batteries. Here, we present the results of magnetic investigations on a Li compound, Li3Ni2RuO6, which was believed to be a ferrimagnet below 80 K. While our neutron diffraction (ND) and isothermal magnetization (M) data support ferrimagnetism, more detailed magnetic studies establish that this ferrimagnetic phase exhibits some features similar to spin-glasses. In addition, we find another broad magnetic anomaly around 40–55 K in magnetic susceptibility (χ), attributable to cluster spin-glass phenomenon. Gradual dominance of cluster spin-glass dynamics with a decrease of temperature (T) and the apparent spread in freezing temperature suggest that the ferrimagnetism of this compound is a chaotic one. The absence of a unique freezing temperature for a crystalline material is interesting. In addition, pyroelectric current (Ipyro) data reveals a feature in the range 40–50 K, attributable to thermally stimulated depolarization current. We hope this finding motivates future work to explore whether there is any intriguing correlation of such a feature with cluster spin-glass dynamics. We attribute these magnetic and electric dipole anomalies to the crystallographic disorder, intrinsic to this compound.

Backbone structure of the Edwards-Anderson spin-glass model

We study the ground-state spatial heterogeneities of the Edwards-Anderson spin-glass model with both bimodal and Gaussian bond distributions. We characterize these heterogeneities by using a general definition of bond rigidity, which allows us to classify the bonds of the system into two sets, the backbone and its complement, with very different properties. This generalizes to continuous distributions of bonds the well-known definition of a backbone for discrete bond distributions. By extensive numerical simulations we find that the topological structure of the backbone for a given lattice dimensionality is very similar for both discrete and continuous bond distributions. We then analyze how these heterogeneities influence the equilibrium properties at finite temperature and we discuss the possibility that a suitable backbone picture can be relevant to describe spin-glass phenomena.

Ferromagnetism and spin-glass-like behavior in (Nd0.65Y0.35)0.7Sr0.3MnO3

We have studied the ferromagnetism and spin-glass-like behavior in polycrystalline perovskite (Nd0.65Y0.35)0.7Sr0.3MnO3 based on investigations of the magnetization, magnetic AC susceptibility, and electron spin resonance (ESR). Magnetization measurements versus temperature reveal a spin-glass phase-transition temperature Tg at about 53 K. For the in-phase susceptibility x′(T), a frequency-dependent peak called the spin-freezing temperature Tf is observed. A lowering of the frequency to zero leads to Tf → Tg. The dynamics of this process was analyzed by means of the slowing-down scaling law τ/τo = (Tf /Tg-1)−zv, where the characteristic time τo and critical exponent zv obtained by fitting the experimental Tf data were about (i.e., 1.6 × 10−15 s) and 10.12, respectively, quite different from those expected for canonical spin-glass systems with τo = 10−13 s and zv = 10. The spin-glass phenomenon is related to the magnetic frustration phenomenon caused by strong competition between ferromagnetic and anti-ferromagnetic interactions, together with the strong magnetic disorder. The dynamics of the magnetic interactions in (Nd0.65Y0.35)0.7Sr0.3MnO3 was studied further by means of ESR.

Influence of volume and Fe local environment on magnetic properties of Fe-rich Fe–Al alloys

Fe-rich Fe–Al alloys present a large variety of magnetic behaviors and mechanical deformation of those alloys affects largely their magnetism. At room temperature alloys can be ferromagnetic, paramagnetic or show magnetic inhomogeneities, and at low temperatures spin-glass and re-entrant spin-glass phenomena have been found. Unfortunately, the mechanisms proposed in the literature to explain the magnetism of these alloys and the increase of the magnetic signal after deformation have discrepancies. This paper, based on Mössbauer spectroscopy measurements, with the support of X-ray diffraction and magnetic measurements performed on annealed and deformed samples and in a wide concentration range, proposes and describes a new way to understand the magnetic behavior of this alloy system. The data obtained from annealed samples confirm that Fe local environment have influence on the intensity of the competing exchange interactions (ferro- and antiferromagnetic). However, it is necessary to take into account the effect of the first and second nearest neighbor shells to explain the different magnetic behaviors found in this system. The data obtained from deformed samples show in addition that Fe–Fe interatomic distance also plays an important role on the magnetic properties of these alloys. When the interatomic distance is increased, the ferromagnetic exchange interaction is favored. The mechanisms described in this report will explain phenomena as the origin of the magnetic inhomogeneities on some of these alloys, as well as its behavior at low temperatures and the increase of magnetization caused by mechanical deformation.

Structural and Magnetic Studies of Ca2−x Sm x MnO Compounds (x=0–0.4)

The Ca2−x Sm x MnO4 (x=0–0.4) compounds were synthesized by a solid–solid method and characterized by XRD at room temperature. The XRD profiles were indexed with a tetragonal structure (I/4mmm space group) for x≤0.3 and orthorhombic one (Pnma space group) for x=0.4. The magnetic measurements were studied as a function of temperature (T=2–300 K) and applied field (μ 0 H=0–10 T). When the temperature decreases, each compound has shown first a ferromagnetic–paramagnetic (FM–PM) transition and then an antiferromagnetic–ferromagnetic (AFM–FM) one. The transition temperatures are found to be Sm-doping dependent. For all compounds, a spin-glass phenomenon is evidenced by FC/ZFC magnetization curves.

Phase diagram and spin-glass phenomena in electron-doped La1−xHfxMnO3 (0.05 ≤ x ≤ 0.3) manganite oxides

The effects of tetravalent hafnium doping on the structural, transport, and magnetic properties of polycrystalline La1−xHfxMnO3 (LHMO) (0.05 ≤ x ≤ 0.3) were investigated systematically. LHMO exhibited a typical colossal magnetoresistance effect via the double-exchange between Mn2+ and Mn3+ ions, instead of that between Mn3+ and Mn4+ ions in hole-doped manganites. A phase diagram was obtained for the first time through magnetization and resistance measurements in a broad temperature range. As the Hf concentration varied from x = 0.05 to 0.3, the Curie point and metal-to-insulator transition temperature increased significantly, whereas the magnetization and resistivity decreased remarkably. An abnormal enhancement of the magnetization was observed at about 42 K. It was further confirmed that a second magnetic phase MnO2 in LHMO gives rise to such a phenomenon. The possible causes are discussed in detail. The dynamic magnetic properties of LHMO, including relaxation and aging processes, were studied, demonstrating a spin-glass state at low temperature accompanied by a ferromagnetic phase.

Comparing the freezing process and the spin-glass phenomenon of the nanopolarization based on the MnO additives PFW–PT relaxors

In this paper, pure and MnO added (1 − x)Pb(Fe 2/3W 1/3)O 3– xPbTiO 3 [(1 − x)PFW– xPT] ceramics are synthesized by using the conventional solid state oxide reaction method. The temperature dependence of the freezing processes is investigated by using the modified-Landau theory. This result is compared with the spin-glass phenomenon. According to the experimental data and the fitting results, the temperature-dependent local order parameters are derived from the modified-Landau theory and the spin-glass model with the experimental data separately and show similar tendencies. Furthermore, the derived local order parameters by using these two models show higher thermal stability by doping MnO additives and decreasing PbTiO 3 contents. In conclusion, the ordering degree of B-site cations is enhanced by increasing PbTiO 3 compositions and is reduced by doping MnO additives. This result is the main mechanism that induces the changes of the temperature-dependent local ordering parameters.

Magnetic and electrical transport properties of nanostructured La 0.67Ca 0.33MnO 3 networks

Contiguously nanostructured networks of La 0.67Ca 0.33MnO 3 (LCMO) are fabricated successfully by pulsed electron deposition (PED) onto the surface of porous anodic alumina oxide (AAO). The Curie temperature ( T C) is about 250 K. The metal–insulator transition temperature ( T p) is about 145 K without the magnetic field. The magnetoresistance can reach 84% near the peak temperature, which suggesting a strong magnetic correlated electronic transportation process. Zero field cooling (ZFC) and field cooling (FC) are split below the paramagnetic–ferromagnetic transition. The ZFC curves exhibit a typical blocking process. The observed spin glass and weak localization phenomena are due to the size effect, and it is found that the resistance dependent temperature curve above metal–insulator transition temperature ( T p) is more suitable to small polaron hopping (SPH) model.

Nonequilibrium relaxation method — an alternative simulation strategy

One well-established simulation strategy to study the thermal phases and transitions of a given microscopic model system is the so-called equilibrium method, in which one first realizes the equilibrium ensemble of a finite system and then extrapolates the results to infinite system. This equilibrium method traces over the standard theory of the thermal statistical mechanics, and over the idea of the thermodynamic limit. Recently, an alternative simulation strategy has been developed, which analyzes the nonequilibrium relaxation (NER) process. It is called theNER method. NER method has some advantages over the equilibrium method. The NER method provides a simpler analyzing procedure. This implies less systematic error which is inevitable in the simulation and provides efficient resource usage. The NER method easily treats not only the thermodynamic limit but also other limits, for example, non-Gibbsian nonequilibrium steady states. So the NER method is also relevant for new fields of the statistical physics. Application of the NER method have been expanding to various problems: from basic first- and second-order transitions to advanced and exotic phases like chiral, KT spin-glass and quantum phases. These studies have provided, not only better estimations of transition point and exponents, but also qualitative developments. For example, the universality class of a random system, the nature of the two-dimensional melting and the scaling behavior of spin-glass aging phenomena have been clarified.

Magnetic properties and specific heat of new spin glass Mn0.5Fe0.5PS3

We have found spin glass phenomena in a layered Mn0.5Fe0.5PS3 compound and investigated its magnetic properties and specific heat. The temperature dependence of the zero field cooled (ZFC) magnetization along the easy axis, M∥ under dc applied field Ha below 1 kOe shows a cusp at Tg=32.6 K. The FC and ZFC curves measured at Ha below 1 kOe separate at almost the same temperature as Tg. For Ha larger than 1 kOe, the temperature at which FC and ZFC curves separate deviates from Tg and shifts toward lower temperature and the peak becomes broader. Magnetic hysteresis is still observed above 70 kOe at 2 K. The remarkable feature of this spin glass phase is that the spin freezing is not suppressed up to a rather high magnetic field compared with similar spin glass (Mn,Fe)TiO3. The cusp temperature of χ′(ω) does not show magnetic field amplitude dependence from 1 to 10 Oe and increases with an increase in frequency, obeying the Vogel–Fulcher rule. The temperature dependence of χ″(ω) shows two extra peaks at Tm1 and Tm2 below Tg. The time dependence of thermoremanent magnetization MTRM below Tg shows power law dependence. The value of the molar specific heat is about an order of magnitude larger than that of MnPS3 and FePS3 at 2 K. The T-linear term characteristic of spin glass is observed below about 10 K. The temperature dependence of the magnetic specific heat shows no anomaly at Tg, Tm1=9 and Tm2=16 K, and shows two peaks at Tc1=13 and Tc2=67 K.

Magnetic hardening and spin-glass phenomena in nanocrystalline FeNbB at low temperatures

The soft nanocrystalline alloy ${\mathrm{Fe}}_{80.5}{\mathrm{Nb}}_{7}{\mathrm{B}}_{12.5},$ containing 25 vol % of bcc Fe, displays a rapid magnetic hardening below 20 K. This interesting process is accompanied by a strong irreversibility between field- and zero-field-cooled magnetizations and by a maximum of the magnetic viscosity near 8 K, both determined in a field of 1 Oe. We investigated the magnetization dynamics in more detail by measuring the linear ac susceptibility ${\ensuremath{\chi}}^{\ensuremath{'}}+i{\ensuremath{\chi}}^{\ensuremath{''}}$ between 30 mHz and 100 kHz. The shifts of the ${\ensuremath{\chi}}^{\ensuremath{''}}$ maxima towards low temperatures with decreasing frequency reveal a critical slowing down of the characteristic time, characterized by a critical exponent $z\ensuremath{\nu}=6.9(2),$ and a collective freezing temperature of ${T}_{g}=7.5\mathrm{K}.$ The collective nature of the freezing is supported by a dynamical scaling analysis of ${\ensuremath{\chi}}^{\ensuremath{''}}(T,\ensuremath{\omega}),$ yielding for the order parameter exponent $\ensuremath{\beta}=0.40(5),$ in good agreement with results for the spin glasses. We discuss these results by assuming a frustration of the exchange in the disordered interfacial regions and by the presence of the weak magnetic Nb-rich shells around the nanocrystalline grains.

Crystal growth, structure and magnetic behavior of ytterbium cobalt gallium oxide YbCoGaO 4

Single crystals of the magnetic oxide YbCoGaO 4 have been grown for the first time. The optical floating zone image furnace was used for this purpose. The obtained single crystal was characterized by X-ray diffraction at room temperature, and refined in the R 3 ̄ m space group, as observed in other members of the LnCoGaO 4 family. Magnetic susceptibility measurements show relatively complex behavior, with classic spin glass phenomena observed below 11 K.

Ferromagnetic-resonance field shift in an exchange-biased CoO/Ni 80Fe 20 bilayer

The temperature dependence of the ferromagnetic resonance field shift has been investigated in a CoO/Permalloy bilayer between room temperature and 4 K. The field shift is found to consist of two components: a unidirectional exchange-bias field shift and a uniaxial anisotropic field shift. These field shifts are shown to be equal to the conventional exchange bias and anisotropy fields, provided the rigid spin rotation hypothesis is correct. We have also measured the temperature variation of the exchange bias and the magnetic anisotropy fields from hysteresis loops obtained from SQUID-magnetometry, and found incomplete agreement with the parameters obtained from the ferromagnetic resonance spectra. Analogies with spin-glass phenomena indicate that this incomplete agreement results from the breakdown of the rigid rotation model (or equivalently, the surface anisotropy model) results due to the large rotation angles encountered in a magnetic moment reversal. Notwithstanding, we show that the results of rotating the sample by 180° in the plane of the film yields changes in the resonance field shift which are in agreement with hysteresis loop parameters. A connection between results observed in exchange bias materials and those in spin-glass materials is suggested.

Phase diagram and mixed phase dynamics of the dilute Ising antiferromagnet Fex Mg1 − xCl2, 0.7 ≤ x ≤ 1

Using magneto-optical techniques, i.e. Faraday rotation, imaging and ‘transparent magnetic circular dichroism’, we have investigated the antiferro-paramagnetic mixed phase of Fex Mg1 −x Cl2, 0.7 <x < 1, in a longitudinal magnetic field H. The observed domain patterns are time and history dependent. The phase boundaries reveal a strong dynamic behaviour at low temperatures, T ≈ 0.1 TN. Spin-glass-like slow relaxation is observed above the mixed phase boundary. At dilution x = 0.7 and T < 2 K, re-entrant spin glass phenomena are observed in fields below the lower mixed phase boundary.

Magnetic properties of Ba 2Cu 3−xM xO 4Cl 2 (M=Ni,Zn)

Similar to the high temperature superconducting compounds, Ba 2Cu 3O 4Cl 2 has the two dimensional Cu|O plane. We investigated the magnetic properties of this compound. It shows the antiferromagnetic behaviors with a canted spin structure below 335K and another magnetic transition like a spin glass phenomena at 33K. With replacing the Cu ion by a small amount of Ni, the magnetic transition at 335K was depressed.

Ferromagnetic properties of potassium clusters incorporated into zeolite LTA.

Ferromagnetic properties are reported for K clusters incorporated into the \ensuremath{\alpha} cage (supercage) of zeolite LTA. In LTA, \ensuremath{\alpha} cages are arrayed in a simple cubic structure with a lattice constant of 12.3 \AA{}. The average 4s-electron number per cluster, n, is systematically changed from 0.8 to 7.3 by controlling the K loading density. Ferromagnetism is observed for 2--3n6--7. The magnetization shows a peak at n\ensuremath{\sim}5, and the average magnetic moment amounts to 0.24${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ per cluster at 100 Oe and 1.7 K. The Curie temperature is n dependent and less than 7 K. Magnetic properties are basically interpreted in terms of the model of itinerant electron ferromagnetism. Narrow energy bands due to the electron transfer between adjacent clusters play an important role in the construction of a model. The magnetic properties exhibit spin-glass and reentrant spin-glass phenomena depending on the K loading density.

Magnetic and thermal properties of ternary Cu-X-Mn alloys

Abstract Specific heat and magnetization measurements have been made in the temperature range 1.7–5.2 K on ternary spin-glass alloys based on Cu–0.25 at.% Mn and Cu-4 at.% Mn. Changes in both the thermal and the magnetic properties with the concentration of a third element (Pt or Al) provide evidence for the importance of the distribution of interaction strengths in determining the details of spin-glass phenomena. A simple scaling hypothesis applied to the thermal data suggests that, whereas the addition of Al to Cu-Mn preserves the binary alloy interaction distribution, the addition of Pt introduces new terms that may be attributable to the Dzyaloshinsky-Moriya interaction.

Experiment on nuclear spin ordering in Sc metal

In order to achieve the nuclear spin ordering in Sc metal, We constructed two stage demagnetization cryostat. Before doing the two stage demagnetized cooling experiment, we measured a temperature dependence of the magnetic susceptibility of Sc metal above 0.25 mK by the one stage demagnetized cooling. Result can be understood by the spin glass phenomenon of iron impurity in Sc metal.