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We explore the existence of spin glass phase in FeCo/FePt bilayers arising due to disordered ferromagnet. The non-ergodic and highly degenerate landscape of the spin glass phase at low temperature explains the origin of complex magnetic texture in the FeCo/FePt system. Upon cooling the bilayered system, the magnetic texture undergoes spin freezing below 120 K as evident from the bifurcations in zero field cooling and field cooling magnetizations at low magnetic field as a manifestation of broken ergodicity. The uncompensated magnetic moments originating in the spin glass state result in slow time dynamics of thermoremanent magnetization. Consequently, the bilayers demonstrate an intriguing magnetic memory effect in which the magnetic state of the system could be retrieved upon isothermal ageing below 120 K after reversing the temperature cycle. Thermal treatment deteriorates the spin glass behaviour and shows a transition to strong ferromagnetic character in FeCo/FePt bilayers. [ABSTRACT FROM AUTHOR]

It is generally believed (but not yet proved) that Ising spin glasses with nearest-neighbor interactions have a phase transition in three and higher dimensions to a low-temperature spin glass phase, but the nature of this phase remains controversial, especially whether it is characterized by multiple incongruent Gibbs states. Of particular relevance to this question is the behavior of the typical free energy difference restricted to a finite volume between two such putative Gibbs states, as well as the nature of the fluctuations of their free energy difference as the couplings within the volume vary. In this paper we investigate these free energy difference fluctuations by introducing a new kind of metastate which classifies Gibbs states through their edge overlap values with a reference Gibbs state randomly chosen from the support of the periodic boundary condition (PBC) metastate. We find that the free energy difference between any two incongruent pure states, regardless of the details of how they’re organized into mixed states within the PBC metastate, converges to a Gaussian (or Gaussian-like) distribution whose variance scales with the volume, proving a decades-old conjecture of Fisher and Huse. The same conclusion applies, though with some additional restrictions, to both mixed Gibbs states and ground states. We discuss some implications of these results. [ABSTRACT FROM AUTHOR]

Motivated by the recent development of quantum technology using quantum annealing technique and the recent works on the static properties of the Sherrington–Kirkpatrick (SK) spin glass model, we study quantum annealing of the spin glass model by tuning both transverse and longitudinal fields. We numerically solve the time-dependent Schrödinger equation of the total Hamiltonian when both the fields are made time-dependent and eventually vanish at the same time. We have computed the time-evolution of the probability of finding the system in one of two degenerate ground states of the classical spin glass. At the end of annealing, using the configuration averaged probability, we have shown a clear advantage while the longitudinal field is annealed rather than keeping it constant throughout the process of quantum annealing. We further investigate the order parameter distribution of a quantum SK spin glass in presence of a small longitudinal field and find, from our exact diagonalization results for small system sizes, evidence for quantum tunneling induced disappearance of the classical Almeida–Thouless phase boundary separating the replica symmetry broken (non-ergodic) and replica symmetric (ergodic) spin glass phase (reported already in 2022). We believe that this longitudinal field induced ergodicity in quantum SK model to be responsible for the observed enhancement of quantum annealing (reported earlier for smaller systems by us in 2014). [ABSTRACT FROM AUTHOR]

The novel potassium sulfido cobaltate, K2[Co3S4] is introduced, with 25% vacancies of the cobalt positions within a layered anionic sublattice. The impedance and dielectric investigations indicate a remarkable ionic conductivity of 21.4 mS cm−1 at room temperature, which is in the range of highest ever reported values for potassium‐ions, as well as a high electrical permittivity of 2650 at 1 kHz, respectively. Magnetometry results indicate an antiferromagnetic structure with giant intrinsic exchange bias fields of 0.432 and 0.161 T at 3 and 20 K respectively, potentially induced by a combination of the interfacial effect of combined magnetic anionic and nonmagnetic cationic sublattices, as well as partial spin canting. The stability of the exchange bias behavior is confirmed by a training effect of less than 18% upon 10 hysteresis cycles. The semiconductivity of the material is determined, both experimentally and theoretically, with a bandgap energy of 1.68 eV. The findings render this material as a promising candidate for both, active electrode material in potassium‐ion batteries, and for spintronic applications. [ABSTRACT FROM AUTHOR]

We prove the Thouless–Anderson–Palmer (TAP) equations for the local magnetization in the multi-species Sherrington–Kirkpatrick (MSK) spin glass model. One of the key ingredients is based on concentration results established in Dey and Wu (J Stat Phys 185(3):22, 2021). The equations hold at high temperature for general MSK model without positive semi-definite assumption on the variance profile matrix Δ 2 . [ABSTRACT FROM AUTHOR]

Abstract The novel potassium sulfido cobaltate, K2[Co3S4] is introduced, with 25% vacancies of the cobalt positions within a layered anionic sublattice. The impedance and dielectric investigations indicate a remarkable ionic conductivity of 21.4 mS cm−1 at room temperature, which is in the range of highest ever reported values for potassium‐ions, as well as a high electrical permittivity of 2650 at 1 kHz, respectively. Magnetometry results indicate an antiferromagnetic structure with giant intrinsic exchange bias fields of 0.432 and 0.161 T at 3 and 20 K respectively, potentially induced by a combination of the interfacial effect of combined magnetic anionic and nonmagnetic cationic sublattices, as well as partial spin canting. The stability of the exchange bias behavior is confirmed by a training effect of less than 18% upon 10 hysteresis cycles. The semiconductivity of the material is determined, both experimentally and theoretically, with a bandgap energy of 1.68 eV. The findings render this material as a promising candidate for both, active electrode material in potassium‐ion batteries, and for spintronic applications.

Recently, Baldwin and Swingle (J Stat Phys 190(7):125, 2023) considered spin glass models with additional conventional order parameters characterizing single-replica properties. These parameters are distinct from the standard order parameter, the overlap, used to measure correlations between replicas. A “min-max” formula for the free energy was prescribed in Baldwin and Swingle (2023). We rigorously verify this prescription in the setting of vector spin glass models featuring additional deterministic spin interactions. Notably, our results can be viewed as a generalization of the Parisi formula for vector spin glass models in Panchenko (Ann Probab 46(2):865–896, 2018), where the order parameter for self-overlap is already present. [ABSTRACT FROM AUTHOR]

We investigate scenarios in which the low-temperature phase of short-range spin glasses comprises thermodynamic states which are nontrivial mixtures of multiple incongruent pure state pairs. We construct a new kind of metastate supported on Gibbs states whose edge overlap values with a reference state fall within a specified range. Using this metastate we show that, in any dimension, the variance of free energy difference fluctuations between pure states within a single mixed Gibbs state with multiple edge overlap values diverges linearly with the volume. We discuss some implications of these results. [ABSTRACT FROM AUTHOR]

Present work reports a systematic study on the evaluation of magnetic inhomogeneities in non-stoichiometric Mg 0·5 Ca 0·5 Fe 2 O 4 nanoferrite (MCNF) by conducting exhaustive dc-magnetization, ac-susceptibility and 57Fe Mössbauer spectroscopic measurements and exchange bias investigations using training protocol down to 6 K. Rietveld fitting to PXRD established the formation of anticipated spinel fcc phase of MCNF (non-stoichiometric) along with a minute impurity phase of calcite. Scherrer method and HRTEM micrographs illustrated broad size distribution of MCNF nanoparticles with an average nanocrystallite size of ∼15 nm. Combined 57Fe Mössbauer spectroscopic and dc-magnetization analysis establishes coexistence of ferrimagnetic (67 %) & superparamagnetic (33 %) states at 300 K with notable M s = 22 emu/g, M r = 4 emu/g & H c = 130 Oe and blocking of most of the nanoparticles of MCNF below 300 K. The coercivity followed the size-modified Kneller law for ferrimagnetic nanoparticles and the saturation magnetization abides the Bloch law. Moreover the frequency-dependent ac-susceptibility investigations revealed two magnetic transitions: (i) A transition at ∼ 330 K in the low frequency data attributed to the relaxation of blocked particles of bigger sizes under the superparamagnetic (SPM) regime and (ii) an irregularity at low temperatures is assigned to surface spin glass freezing. Surface spin glass freezing was further affirmed by the ageing experiments and dynamic scaling law. Furthermore, even the best fit to the dynamic scaling couldn't assert the existence of conventional spin glass phase due to slower spin-flip time of surface spins. A soft ferrimagnetic core of MCNF is enveloped with disordered surface spins, which manifest spin glass state. Concurrently, the findings of exchange bias at 30 K and training effect at 6 K affirmed that MCNF nanoparticles are presenting themselves as FM core- SG shell system. Our experimental findings suggested magnetic inhomogeneities comprised of superparamagnetism, ferrimagnetism and disordered surface spin glass state in the non-stoichiometric MCNF. [ABSTRACT FROM AUTHOR]

This paper focuses on characterizing the energy profile along pathways connecting different regions of configuration space in the context of a prototypical glass model, the pure spherical p -spin model with p = 3. The study investigates pairs of stationary points (local minima or rank-1 saddles), analyzing the energy profile along geodesic paths and comparing them with 'perturbed' pathways correlated to the landscape curvature. The goal is to assess the extent to which information from the local Hessian matrices around stationary points can identify paths with lower energy barriers. Surprisingly, unlike findings in other systems, the direction of softest local curvature is not a reliable predictor of low-energy paths, except in the case in which the direction of softest curvature corresponds to an isolated mode of the Hessian. However, other information encoded in the local Hessian does allow the identification of pathways associated with lower energy barriers. We conclude commenting on implications for the system's activated dynamics. [ABSTRACT FROM AUTHOR]

We establish relations between different characterizations of order in spin glass models. We first prove that the broadening of the replica overlap distribution indicated by a nonzero standard deviation of the replica overlap R 1 , 2 implies the non-differentiability of the two-replica free energy with respect to the replica coupling parameter λ . In Z 2 invariant models such as the standard Edwards–Anderson model, the non-differentiability is equivalent to the spin glass order characterized by a nonzero Edwards–Anderson order parameter. This generalization of Griffiths’ theorem is proved for any short-range spin glass models with classical bounded spins. We also prove that the non-differentiability of the two-replica free energy mentioned above implies replica symmetry breaking in the literal sense, i.e., a spontaneous breakdown of the permutation symmetry in the model with three replicas. This is a general result that applies to a large class of random spin models, including long-range models such as the Sherrington-Kirkpatrick model and the random energy model. There is a 25-minute video that explains the main results of the present work: [ABSTRACT FROM AUTHOR]

It is rigorously shown that an appropriate quantum annealing for any finite-dimensional spin system has no quantum first-order transition in transverse magnetization. This result can be applied to finite-dimensional spin-glass systems, where the ground state search problem is known to be hard to solve. Consequently, it is strongly suggested that the quantum first-order transition in transverse magnetization is not fatal to the difficulty of combinatorial optimization problems in quantum annealing. [ABSTRACT FROM AUTHOR]

The magnetic susceptibility of Fe1 –xCoxCr2S4 solid solutions in the FeCr2S4-rich part of the FeCr2S4–CoCr2S4 system has been studied by static and dynamic methods. The magnetic measurements were performed at temperatures from 5 to 300 K in static (50 Oe and 45 kOe) and ac magnetic fields (field amplitude Hac = 1 Oe; ac field frequencies ν = 100, 1000, and 10 000 Hz). We have determined the temperatures of the magnetic transformations in the system and identified their nature. The results demonstrate that the temperature of the ferrimagnetic phase transition (TC) in Fe1 –xCoxCr2S4 increases with increasing cobalt content. The materials with x = 0–0.5 have been shown to undergo a transition to a spin glass state, evidenced by a shift of maxima in temperature dependences of the imaginary part of their dynamic susceptibility. [ABSTRACT FROM AUTHOR]

Copyright of Journal of the Chinese Society of Rare Earths is the property of Editorial Department of Journal of the Chinese Society of Rare Earths and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The layered crystal structure of Cr2Ge2Te6 shows ferromagnetic ordering at the two‐dimensional limit, which holds promise for spintronic applications. However, external voltage pulses can trigger amorphization of the material in nanoscale electronic devices, and it is unclear whether the loss of structural ordering leads to a change in magnetic properties. Here, it is demonstrated that Cr2Ge2Te6 preserves the spin‐polarized nature in the amorphous phase, but undergoes a magnetic transition to a spin glass state below 20 K. Quantum‐mechanical computations reveal the microscopic origin of this transition in spin configuration: it is due to strong distortions of the CrTeCr bonds, connecting chromium‐centered octahedra, and to the overall increase in disorder upon amorphization. The tunable magnetic properties of Cr2Ge2Te6 can be exploited for multifunctional, magnetic phase‐change devices that switch between crystalline and amorphous states. [ABSTRACT FROM AUTHOR]

We investigate the structural and magnetic properties of a Fe–Ti–O system prepared by ball-milling and post annealing from γ -Fe 2 O 3 and TiO 2 -anatase. From a systematic analysis of the structural properties, we show that our sample consists of a Fe–Ti–O solid solution, in which the Ti acts as dopant in the hematite structure. Moreover, by exploring distinct aspects of the magnetic behavior, we reveal that our sample presents a magnetic behavior that is strongly dependent on the temperature. Although the Fe–Ti–O solid solution carries the ordinary magnetic behavior expected for the hematite over most of the investigated temperature range, we verify quite-interesting features of magnetic origin taking place at lower temperatures. We interpret them as fingerprints of cluster spin freezing effect and provide experimental evidence supporting the existence of the glassy state below ∼ 51 K. [ABSTRACT FROM AUTHOR]

The existence theorem for replica-symmetry breaking (RSB) in the transverse field Sherrington–Kirkpatrick (SK) model is extended to the model with a general random exchange interactions. The relation between the expectation value of the exchange interaction energy and the Duhamel correlation function of spin operators can be obtained by an approximate integration by parts for general random interactions. In addition to the Falk–Bruch inequality, these explicit evaluations enable us to prove that the variance of overlap between two replica spin operators does not vanish under sufficiently weak transverse field in sufficiently low temperature. The absence of the ferromagnetic long range order is also shown to distinguish RSB from the Z 2 -symmetry breaking. [ABSTRACT FROM AUTHOR]

Abstract The layered crystal structure of Cr2Ge2Te6 shows ferromagnetic ordering at the two‐dimensional limit, which holds promise for spintronic applications. However, external voltage pulses can trigger amorphization of the material in nanoscale electronic devices, and it is unclear whether the loss of structural ordering leads to a change in magnetic properties. Here, it is demonstrated that Cr2Ge2Te6 preserves the spin‐polarized nature in the amorphous phase, but undergoes a magnetic transition to a spin glass state below 20 K. Quantum‐mechanical computations reveal the microscopic origin of this transition in spin configuration: it is due to strong distortions of the CrTeCr bonds, connecting chromium‐centered octahedra, and to the overall increase in disorder upon amorphization. The tunable magnetic properties of Cr2Ge2Te6 can be exploited for multifunctional, magnetic phase‐change devices that switch between crystalline and amorphous states.

Efficient sampling and approximation of Boltzmann distributions involving large sets of binary variables, or spins, are pivotal in diverse scientific fields even beyond physics. Recent advances in generative neural networks have significantly impacted this domain. However, these neural networks are often treated as black boxes, with architectures primarily influenced by data-driven problems in computational science. Addressing this gap, we introduce a novel autoregressive neural network architecture named TwoBo, specifically designed for sparse two-body interacting spin systems. We directly incorporate the Boltzmann distribution into its architecture and parameters, resulting in enhanced convergence speed, superior free energy accuracy, and reduced trainable parameters. We perform numerical experiments on disordered, frustrated systems with more than 1000 spins on grids and random graphs, and demonstrate its advantages compared to previous autoregressive and recurrent architectures. Our findings validate a physically informed approach and suggest potential extensions to multivalued variables and many-body interaction systems, paving the way for broader applications in scientific research.

Here, the structural, magnetic, and dielectric features of breathing pyrochlore LiInCr _4−x Co _x O _8 were investigated. The XRD analysis showed changes in Cr–Cr length and distorted CrO _6 octahedral as Co ion doping level rises. The x-ray photoemission spectroscopy measurements showed that there are both Co ^2+ and Co ^3+ ions in the LiInCr _4−x Co _x O _8 compounds. The difference between temperature-dependent magnetization curves during field cooling and zero-field cooling suggested that there is a spin-glass state, which was verified by the heat capacity measurement. Doping affects the bond length, which affects the magnetic properties and electronic properties. The dielectric characteristics were systematically studied, and the temperature dependence of the dielectric loss and dielectric constant was examined in the temperature range of 323−573 K at various frequencies. The dielectric behavior strongly changes with the change in temperature and/or frequency. The activation energies of grain boundary resistance of doped samples show a decreasing trend with increasing doping.

Abstract Exchange bias has increasingly practical significance in magnetoresistive and spintronic devices. However, the underlying mechanism of exchange bias in bulk compounds with the structural single‐phase and inhomogeneous magnetic phases is still elusive. Herein, based on experimental and simulation results, two important parameters are studied, i.e., the antiferromagnetic (AFM) volume fraction and the ferromagnetic (FM)/AFM interface area, which essentially determine the (spontaneous) exchange bias of Mn‐rich Ni44Co6Mn44‐xSn6+x (x = 0 ∼ 6) magnetic shape memory alloys. The substitution Sn for Mn changes magnetic ground state following the sequence of superparamagnetic/AFM → dilute spin glass/AFM → transition zone → cluster spin glass/AFM → FM, accompanying the growth of FM cluster and the weakening of AFM interactions. The results reveal that the magnetic ground state for exchange bias is optimized at transition zone between dilute spin glass/strong AFM and cluster spin glass/weak AFM, in which the optimal AFM volume fraction and FM/AFM interface area are achieved by tuning magnetic fields. A giant exchange bias field of 702.7 mT and a spontaneous exchange bias field of 318.7 mT are demonstrated. The work contributes to in‐depth understanding of (spontaneous) exchange bias in magnetically inhomogeneous compounds.

Nickel and Cobalt ion containing silica based nanoglasses confined within mesoporous SBA-15 and mesoporous alumina templates were synthesized by sol-gel process. These nanocomposites were investigated to understand their microstructure, magnetization dynamics and magnetic memory effects near transition temperatures using state-of-the-art characterization techniques including XRD, TEM and SQUID. The temperature and frequency dependent dielectric properties and Nyquist plot were also investigated. The effect of transition ions and template on memory effect and relaxation dynamics of spin glass phase were explained with Scaling and Vogel-Fulcher laws. The mechanism accountable for the observed characteristics of these nanoconfined amorphous systems are explained systematically. The polarization mechanisms as a function of temperature and frequency were also investigated comprehensively. This study provides an advanced understanding of magnetization dynamics and dielectric property in nanoglass system which will be of fundamental and technological interest that will help to tune and fabricate advanced functional nano materials.

ABO3 perovskite materials with small cations at the A site, especially those with ordered cation arrangements, have attracted a great deal of interest because they show unusual physical properties and deviations from the general characteristics of perovskites. In this work, perovskite solid solutions (Lu0.5Mn0.5)(Mn1−xTix)O3 with x = 0.25, 0.50, and 0.75 were synthesized by means of a high-pressure, high-temperature method at approximately 6 GPa and approximately 1550 K. All the samples crystallize in the GdFeO3-type perovskite structure (space group Pnma) and have random distributions of the small Lu3+ and Mn2+ cations at the A site and Mn4+/3+/2+ and Ti4+ cations at the B site, as determined by Rietveld analysis of high-quality synchrotron X-ray powder diffraction data. Lattice parameters are a = 5.4431 Å, b = 7.4358 Å, c = 5.1872 Å (for x = 0.25); a = 5.4872 Å, b = 7.4863 Å, c = 5.2027 Å (for x = 0.50); and a = 5.4772 Å, b = 7.6027 Å, c = 5.2340 Å (for x = 0.75). Despite a significant dilution of the A and B sublattices by non-magnetic Ti4+ cations, the x = 0.25 and 0.50 samples show long-range ferrimagnetic order below TC = 89 K and 36 K, respectively. Mn cations at both A and B sublattices are involved in the long-range magnetic order. The x = 0.75 sample shows a spin-glass transition at TSG = 6 K and a large frustration index of approximately 22. A temperature-independent dielectric constant was observed for x = 0.50 (approximately 32 between 5 and 150 K) and for x = 0.75 (approximately 50 between 5 and 250 K). [ABSTRACT FROM AUTHOR]

The space of possible human cultures is vast, but some cultural configurations are more consistent with cognitive and social constraints than others. This leads to a "landscape" of possibilities that our species has explored over millennia of cultural evolution. However, what does this fitness landscape, which constrains and guides cultural evolution, look like? The machine-learning algorithms that can answer these questions are typically developed for large-scale datasets. Applications to the sparse, inconsistent, and incomplete data found in the historical record have received less attention, and standard recommendations can lead to bias against marginalized, under-studied, or minority cultures. We show how to adapt the minimum probability flow algorithm and the Inverse Ising model, a physics-inspired workhorse of machine learning, to the challenge. A series of natural extensions—including dynamical estimation of missing data, and cross-validation with regularization—enables reliable reconstruction of the underlying constraints. We demonstrate our methods on a curated subset of the Database of Religious History: records from 407 religious groups throughout human history, ranging from the Bronze Age to the present day. This reveals a complex, rugged, landscape, with both sharp, well-defined peaks where state-endorsed religions tend to concentrate, and diffuse cultural floodplains where evangelical religions, non-state spiritual practices, and mystery religions can be found. [ABSTRACT FROM AUTHOR]

Ti-doped maghemite nanoparticles of average crystallite size 12.9 nm were synthesized using the sol–gel method. The XRD profile mainly showed the presence of maghemite phase with very small phases of TiO2 (rutile and anatase). Magnetization hysteresis loops of the nanoparticles were obtained between −4 T to +4 T at temperatures of 2, 10, 30, 50, 70, 100, 150, 200, and 300 K under field cooling (FC) of 1, 2, 3, and 4 T and zero-field cooling conditions (ZFC). The coercivity displayed nonmonotonic field dependence while it decreased sharply with temperature and vanished at 150 K at all fields. Horizontal hysteresis loop shifts were observed in the 2–150 K temperature range in both the ZFC and FC conditions. The exchange bias effect became negligible in both ZFC and FC states above 50 K. Magnetization vs. applied field measurements were conducted in both ZFC and FC cooled conditions at several temperatures in the range of 2–400 K, with spin freezing being observed below 50 K. The exchange bias effect obtained below 50 K is suggested to be attributed to the competing roles of the long-range dipolar and short-range exchange coupled interactions. [ABSTRACT FROM AUTHOR]

Nanoparticles of Co-doped copper ferrite, Cu 0.75 Co 0.25 Fe 2 O 4 , were successfully synthesized by hydrothermal method. The preparation conditions were optimized to produce small nanoparticles with crystallite size of 20 nm that fall into the single-domain regime. The influence of Co-doping on the structure and magnetic properties of pure copper ferrite, CuFe 2 O 4 , was investigated. The prepared ferrite nanoparticles were found to be in a single structural phase with a spinel-type structure, according to the XRD and FT-IR measurements. When compared to pure Cu ferrite, the addition of Co increased the lattice constant and decreased the density. The TEM results confirmed the spherical morphology of the prepared ferrite nanoparticles. For the entire temperature range of the ferrite nanoparticles, the magnetization measurements showed a single ferrimagnetic phase. It was observed that the coercivity and remanent magnetization increased with decreasing temperature. Magnetic anisotropy was found to increase with Co-doping in comparison to pure Cu ferrite. The ZFC–FC magnetization curves showed that the blocking temperature ( T B ) of the prepared nanoparticles is above room temperature, demonstrating that they are ferrimagnetic at room temperature and below. Additionally, it was found that decreasing the magnetic field lowers T B . The FC curves below T B were observed to be nearly flat, indicating spin-glass behavior that might be attributed to nanoparticle interactions and/or surface effects such as spin canting and spin disorder. [ABSTRACT FROM AUTHOR]

In this work, the impact of milling time on the structural, morphological, and magnetic properties is investigated in SmFeO 3 (SFO) powders obtained by solid state reaction. Specifically, the ball milling process is incorporated as an intermediate step during the synthesis and their magnetic properties vary when the samples are milled for 4 and 10 h. Based on X-ray diffraction, the resulting samples crystallized in Pbnm space group, with a slight decrease in crystallite size and cell volume with milling time. These results are also supported by confocal Raman microscopy with a slight shift towards lower wavenumbers. In this sense, magnetic characterization demonstrates a weak ferromagnetic contribution coexisting with the dominant antiferromagnetic order. Butterfly shaped hysteresis loops are observed in both samples for T > 200 K while a single shaped loop is achieved for T < 200 K. Zero field cooled, and field cooled magnetization curves shows a broad maximum centered at 140 K and bifurcation of the two curves because of the competing interaction between the Sm+3 and Fe3+ ions into the SFO crystal structure. Interestingly, exchange bias (EB) effect is found up to 200 K with a field cool of 20 kOe for both samples. The existence of Fe–Fe, Fe–Sm, and Sm–Sm interactions in a cluster glass state induced by ball milling processes might be the main cause of such EB effect. • The impact of ball milling as an intermediate state of the synthesis reveals important changes in the magnetic properties. • Butterfly shaped hysteresis loops are observed in both samples for T > 200 K while a single shaped loop is achieved for T < 200 K. • Strong competition between Sm_4f and Fe_3d electrons may arise to the bifurcation between the ZFC and FC magnetization curves. • Exchange bias (EB) effect is found up to 200 K with a field cool of 2 T for the SmFeO 3 samples. [ABSTRACT FROM AUTHOR]

The magnetic properties of the Co 1-x Fe x Cr 2 S 4 solid solutions for compositions adjacent to CoCr 2 S 4 were investigated using various techniques, including magnetization measurements and AC susceptibility. The results revealed that substituting Fe for Co in the CoCr 2 S 4 compound led to changes in the magnetic behavior, such as the presence of ferrimagnetic ordering and the emergence of a cluster spin glass phase. The study found that the temperature of the ferrimagnetic transition (T C) decreased with increasing Fe concentration, indicating the influence of iron on the magnetic properties of the solid solutions. Additionally, the discovery of a cluster spin glass phase for specific compositions (x = 0, 0.1, 0.2, 0.4) suggests complex magnetic behavior in these materials. In summary, the study offers valuable insights into the magnetic properties of Co 1-x Fe x Cr 2 S 4 solid solutions and highlights the potential for tuning their magnetic behavior through compositional variations. [ABSTRACT FROM AUTHOR]

• Structural and magnetic properties of polycrystalline Pr 1.8 La 0.2 CoFeO 6 sample have been explored. • Pr 1.8 La 0.2 CoFeO 6 adopts orthorhombic structure with space group Pnma. • XPS study reveals mixed valence state Fe3+/Fe4+ and Co2+/Co3+ ions in the system. • Magnetization data demonstrate Griffiths phase, exchange bias and cluster glass. • Raman study shows signature of spin phonon coupling in the system. The structural and magnetic properties of the double perovskite P r 1.8 L a 0.2 C o F e O 6 have been investigated. The X-ray diffraction study shows that the system acquires room-temperature orthorhombic phase with the Pnma space group. The X-ray photoemission spectroscopy (XPS) measurement confirmed that the B-site ions are present in mixed valence states i.e. Co has been found in Co2+ and Co3+ valance states whereas Fe has been found in Fe3+/Fe4+. Magnetic measurements of the system confirm the existence of several fascinating magnetic behaviors, such as long-range canted antiferromagnetism with T N ∼ 271 K, giant exchange bias, and re-entrant cluster glass phase (T G ∼ 33 K). Field-dependent magnetization shows a large spontaneous exchange bias; H S E B ∼ 1.8 kOe and giant conventional exchange bias, H C E B ∼ 2.4 kOe at 5 K. Antiferromagnetic materials with large exchange bias can be utilized in high-density spintronic devices. Temperature-dependent Raman study demonstrates that the observed phonon mode exhibits anomalous behavior close to the magnetic transition temperature. Analysis of anomalous softening of phonon mode below T N , clarifies the presence of significant spin-phonon coupling while the magnetostriction effect does not play any significant role in the observed phonon anomaly. [ABSTRACT FROM AUTHOR]

Recent research has highlighted the significance of perovskites owing to their diverse characteristics arising from the integration of elements across the periodic table. The properties of these materials are influenced through a range of factors, including constituent elements, disorder, oxygen deficiency, and so on. We investigated the impact of disorder, along with the dependency of temperature and cooling field on exchange bias, using both experimental and theoretical simulations. Improving B-site disorder led to a significant enhancement (18.6 kOe) in the exchange bias of SrFe 0.45 Co 0.45 Ir 0.1 O 3 , due to numerous new interactions and a reduction in the size of magnetic clusters. Our findings highlight the critical impact of purposeful material design techniques, specifically the importance of B-site disorder in structures in facilitating the giant exchange bias. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] A series of layered solid solutions Y 2- x Fe 1+ x TaO 7 (x = 0–0.2) was synthesized and a structural transition (space group R 3 ¯ ↔ space group P 3 1 21) was observed at x = 0.1. In Y 2− x Fe 1+ x TaO 7 , which belongs to both structural types, geometrically frustrated 2D sublattices of kagome-type are formed, in which Fe3+ ions are coupled by short-range antiferromagnetic interactions, and the transition to the spin glass state is observed at T g ∼ 4.3 K. A phenomenon of weak ferromagnetism has been detected, the cause of which is probably a small tilt of the Fe3+ spins due to the Dzyaloshinskii–Moriya antisymmetric superexchange. [ABSTRACT FROM AUTHOR]

We revisit the Haakeâ€"Lewensteinâ€"Wilkens approach to Edwardsâ€"Anderson (EA) model of Ising spin glass (SG) (Haake et al 1985 Phys. Rev. Lett. 55 2606). This approach consists in evaluation and analysis of the probability distribution of configurations of two replicas of the system, averaged over quenched disorder. This probability distribution generates squares of thermal copies of spin variables from the two copies of the systems, averaged over disorder, that is the terms that enter the standard definition of the original EA order parameter, q EA . We use saddle point/steepest descent (SPSD) method to calculate the average of the Gaussian disorder in higher dimensions. This approximate result suggest that q EA > 0 at 0 < T < T c in 3D and 4D. The case of 2D seems to be a little more subtle, since in the present approach energy increase for a domain wall competes with boundary/edge effects more strongly in 2D; still our approach predicts SG order at sufficiently low temperature. We speculate, how these predictions confirm/contradict widely spread opinions that: (i) There exist only one (up to the spin flip) ground state in EA model in 2D, 3D and 4D; (ii) there is (no) SG transition in 3D and 4D (2D). This paper is dedicated to the memories of Fritz Haake and Marek Cieplak. [ABSTRACT FROM AUTHOR]

Silver–nickel bimetallic nanowire-containing transparent thin films (TFs) were investigated for their electrical and magnetic properties. A facile sol–gel technique followed by an electrodeposition process was used to fabricate these samples. X-ray diffraction and X-ray photoelectron spectroscopy were utilized to characterize the constituent elements and to explain their electrical and magnetic properties. Scanning electron microscopy and transmission electron microscopy provided the details of microstructural features. Zero field cooled (ZFC) and field cooled (FC) studies indicated the existence of spin glass (SG), which was thoroughly investigated following FC and ZFC memory effects along with relaxation dynamic studies. Scaling law and Vogel–Fulcher law substantiated the presence of the SG phase. Magnetodielectric results were explained using Catalan's model assuming positive magnetoresistance. The magnetic field-dependent charge transport mechanism explained the magnetoelectric coupling and spin transport properties as a function of electric and magnetic fields. A realistic circuit model with contributions from each component as a function of the magnetic field was also discussed considering the Nyquist plot. This study offers useful insights on bimetallic nanowire-based TFs leading to the possible fabrication of magnetic sensor devices. [ABSTRACT FROM AUTHOR]

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In order to investigate the size dependence of magnetic properties in the single-domain and superparamagnetic regimes, zinc ferrite ZnFe 2 O 4 nanoparticles were synthesized with sizes around 15 nm by the hydrothermal method. The zinc ferrite nanoparticles were characterized by XRD, TEM, FT-IR, and VSM. According to the Rietveld refinement results, the nanoparticles exhibited a cubic single-phase spinel-type structure. The TEM observations indicated that the nanoparticles were spherical in shape. The FT-IR analysis revealed two dominant absorption bands, confirming the formation of a single-phase spinel structure with two sub-lattices: tetrahedral and octahedral. Magnetic measurements conducted over a wide range of temperatures and magnetic fields revealed that the ferrite nanoparticles were ferrimagnetic dressed with spin-glass behavior below the blocking temperature ( T B ) and superparamagnetic above T B . The saturation magnetization and the first anisotropy constant of the nanoparticles were found to increase with decreasing temperature. The superparamagnetic critical size, D SP , of the nanoparticles was found to be about 13 nm, suggesting that the prepared ferrite nanoparticles were within the superparamagnetic regime, and thus by implication within the single domain regime. [ABSTRACT FROM AUTHOR]

Here a spin glass system with emergent planar ordered spin clusters is investigated. The mixed B-site pyrochlore Gd 2 ScNbO 7 has been synthesized and characterized through a variety of techniques, including x-ray diffraction, magnetic susceptibility, muon spin relaxation, heat capacity and neutron scattering. Despite a Curie-Weiss temperature of -3.93(3) K, indicating net antiferromagnetic interactions, no signs of long ranged magnetic ordering are found down to T = 0.3 K. Instead, a disordered magnetic state emerges with a small correlation length of 2.1(1) Å of single tetrahedra. A Reverse Monte Carlo analysis of the polarized neutron scattering data reveals short-range antiferromagnetic order with emergent XY spin ordering similar to the parent pyrochlore compounds. Muon spin relaxation, and AC susceptibility measurements confirm that the magnetization condenses into a glass, with 10 % of the potential entropy missing in the specific heat. This magnetic ground state is similar to what is observed in Gd 2 Sn 2 O 7 just above the ordering temperature, without the eventual long-range ordering at low temperature., (Creative Commons Attribution license.)

Tuning magnetic properties in layered van der Waals (vdW) materials has captured significant attention due to the efficient control of ground states by heterostructuring and external stimuli. Electron doping by electrostatic gating, interfacial charge transfer, and intercalation is particularly effective in manipulating the exchange and spin-orbit properties, resulting in a control of Curie temperature (T C ) and magnetic anisotropy. Here, an uncharted role of intercalation is discovered to generate magnetic frustration. As a model study, Na atoms are intercalated into the vdW gaps of pristine Cr 2 Ge 2 Te 6 (CGT) where generated magnetic frustration leads to emerging spin-glass states coexisting with a ferromagnetic order. A series of dynamic magnetic susceptibility measurements/analysis confirms the formation of magnetic clusters representing slow dynamics with a distribution of relaxation times. The intercalation also modifies other macroscopic physical parameters including the significant enhancement of T C from 66 to 240 K and the switching of magnetic easy-hard axis direction. This study identifies intercalation as a unique route to generate emerging frustrated spin states in simple vdW crystals., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

The CoCr0.5Ga1.5S4 compound has been synthesized and shown to crystallize in trigonal symmetry (P3m1) with unit-cell parameters а = 3.639 Å and с = 12.016 Å. Its magnetic properties have been measured in the temperature range 4–300 K in static magnetic fields of 50 Oe and 45 kOe and in an ac magnetic field (10, 100 and 1000 Hz) with a modulation amplitude of 1 Oe. According to the results obtained by measuring its magnetic properties, the compound is a ferrimagnet with an ordering temperature TC = 205 K. Temperature dependences of the imaginary part of its dynamic magnetic susceptibility obtained during cooling show a cusp with a frequency dependence indicative of a transition to a reentrant spin glass state at Tf ~ 12 K. [ABSTRACT FROM AUTHOR]

We solve the random energy model when the energies of the configurations take only integer values. In the thermodynamic limit, the average overlaps remain size dependent and oscillate as the system size increases. While the extensive part of the free energy can still be obtained by a standard replica calculation with one step replica symmetry breaking, it is no longer possible to recover the overlaps in this way. A possible way to adapt the replica approach is to allow the sizes of the blocks in the Parisi matrix to fluctuate and to take complex values. [ABSTRACT FROM AUTHOR]

Here we present the Mössbauer study of the combined magnetic and electrical hyperfine interactions of the probe 57Fe nuclei localized in the hexagonal manganite ScMnO 3. The hyperfine interactions were measured in the temperature range where ScMnO 3 demonstrates spin ordering: 15 K < T < T N (∼ 130 K). By analyzing the hyperfine parameters of 57Fe nuclei, we evaluated the oxidation state of the iron ions, their local crystal environment, and the orientation of the magnetic moments μ Fe in the structure of ScMn 0.996 57Fe 0.004 O 3 at T << T N. The temperature-dependent evolution of Zeeman structures in Mössbauer spectra was analyzed using the stochastic relaxation model, and indicates the presence of frustration of the superexchange interactions Fe3+−O−Mn3+. The temperature dependence of the hyperfine magnetic field B hf (T) was described using critical indices, whose values reflect the reduced dimensionality of the magnetic system under study. It was shown that the observed sharp temperature-dependent change of the quadrupole shift of the Zeeman structure components may be attributed to the spin reorientation process, resulting in antiferromagnetism with a weak ferromagnetic component. • Mössbauer measurements of hexagonal ScMnO 3 in a wide temperature range including Néel and spin-glass transition points. • Combined thermodynamical and magnetic measurements in a wide temperature range. • The stochastic relaxation model for analysis of the temperature-dependent hyperfine Zeeman structure of probe 57Fe nuclei. • Spin-glass state and frustrated spin-spin Fe-O-Mn interactions. • The spin reorientation process and antiferromagnetism with a weak ferromagnetic component. [ABSTRACT FROM AUTHOR]

• Annealing effect on structural property correlation in Mn 2 Ni 1.6 Sn 0.4 ribbons fabricated from RF induction melted bulk. • The coexistence of cubic inverse Heusler XA and orthorhombic crystal symmetries. • The magnetic ordering near T C follows the 3D-Heisenberg model, and at T≪T C, it follows the Bloch law. • The high-temperature resistivity data is consistent with the electron–phonon scattering. • Low-temperature ρ T data for as-synthesized and 600 °C annealed ribbons supports the existence of the spin glass state. We investigate the consequences of annealing on the structure, microstructure, magnetic, and electrical transport of Mn 2 Ni 1.6 Sn 0.4 ribbons. The 40–60 μm thick ribbons were formed by melt spinning of the bulk ingot synthesized by RF induction melting. Ribbons were annealed at 600 °C for 12 hrs and the other at 800 °C for 2 hrs in vacuum. All ribbons crystallize into a cubic symmetry (space group F 4 ¯ 3 m). The orthorhombic phase appears as the secondary one. In ribbons annealed at 600 °C, the crystallite size decreases from ∼ 47 nm to ∼ 29 nm, and annealing at 800 °C doubles the crystallite size to ∼ 96 nm. The least amount of microstrains (17x10−4) in the as-synthesized ribbon is consistent with the occurrence of the superlattice peaks (111) and (200). Lower intensities of the superlattice peaks in 600 °C and 800 °C ribbons are consistent with higher microstrains (25x10−4 and 24x10−4). Hence, a higher degree of Ni-Mn ordering improves magnetic properties in annealed samples. The as-synthesized ribbon has an austenite-phase Curie temperature of T C A ∼ 303 K , which enhances to T C A ∼ 320 K and T C A ∼ 310 K after annealing at 600 °C and 800 °C. The ribbon annealed at 600 °C has the highest saturation moment. All the ribbons show the exchange-bias (EB) effect, and the most pronounced effect is seen in the 800 °C annealed ribbon. Microstructure uniformization and relative strengths of the Ni-Mn and Mn-Mn interactions improve the magnetics. Near T C , M T = M 0 T C - T β is satisfied (β = 0.31, 0.36, and 0.37, for as-synthesized, 600 °C and 800 °C annealed ribbons). The low-temperature spontaneous magnetization obeys the Bloch law M T = M 0 1 - A T 3 2 , with a deviation in 600 °C annealed ribbon due to spin freezing. The ρ-T has been fitted in the different temperature ranges using the various combinations in ρ T = ρ 0 + A p h T + B s d T α. At T < 85 K, the resistivity of the as-synthesized ribbon follows ρ T = ρ 0 + B s d T α , with α ≈ 1.47 , while for the 600 °C annealed ribbon, α ≈ 1.49. The exponent α ∼ 1.5 supports the existence of the spin glass state in the lower temperature region of as-synthesized and 600 °C annealed ribbons. In the high-temperature range, the linear ρ-T behavior is described by ρ T = ρ 0 + A p h T and consistent with the electron–phonon scattering. [ABSTRACT FROM AUTHOR]