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This study explores the enhancement in magnetic and photoluminescence properties of Mn2+‐doped (CdSe)13 nanoclusters, significantly influenced by the introduction of paramagnetic centers through doping, facilitated by optimized precursor chemistry and precisely controlled surface ligand interactions. Using a cost‐effective and scalable synthesis approach with elemental Se and NaBH4 (Se‐NaBH4) in n‐octylamine, we tailored bonding configurations (Cd−O, Cd−N, and Cd−Se) on the surface of nanoclusters, as confirmed by EXAFS analysis. These bonding configurations allowed for tunable Mn2+‐doping with tetrahedral coordination, further stabilized by hydrogen‐bonded acetate ligands, as evidenced by 13C NMR and IR spectroscopy. Mulliken charge analysis indicates that the charge redistribution on Se2− suggests electron transfer between surface ligands and the nanocluster, contributing to spin fluctuations. These tailored configurations markedly increased the nanoclusters′ magnetic susceptibility and photoluminescence efficiency. The resulting nanoclusters demonstrated a clear concentration‐dependent response in emission lifetimes and intensities upon exposure to magnetic field effects (MFE) and spin‐spin coupling, alongside a large magnetic moment exceeding 40 μB at 180 K. These findings highlight the potential of these nanoclusters for magneto‐optical devices and spintronic applications, showcasing their tunable magnetic properties and exciton dynamics. [ABSTRACT FROM AUTHOR]

Spin‐orbit coupling (SOC) has significant effects on the superconductivity and magnetism of transition metal dichalcogenides (TMDs) at the 2D limit. Although 2D TMD samples possess many exotic properties different from those of bulk samples, experimental characterization in this field is still limited, especially for magnetism. Recent studies have revealed that bulk misfit layer compounds (MLCs) with (LaSe)1.14(NbSe2)n = 1,2 exhibit an Ising superconductivity similar to that of heavily electron‐doped NbSe2 monolayers. This offers an opportunity to study the effect of SOC on the magnetism of 2D TMDs. Here, the possible SOC effect in (LaSe)1.14(NbSe2) is investigated by measuring nuclear magnetic resonance (NMR) and electrical transport. It is found that the LaSe layer not only functions as a charge reservoir for transferring electrons into the NbSe2 layer but also remarkably influences the local electronic environment around the 93Nb nuclei. More importantly, the significant SOC induces both a weak antilocalization (WAL) effect and anisotropic spin fluctuations in noncentrosymmetric NbSe2 layers. The present work contributes to a deep understanding of the role of the SOC effect in 2D TMDs and supports MCLs as an intriguing platform for exploring exotic physical properties within the 2D limit. [ABSTRACT FROM AUTHOR]

Spin‐orbit coupling (SOC) has significant effects on the superconductivity and magnetism of transition metal dichalcogenides (TMDs) at the 2D limit. Although 2D TMD samples possess many exotic properties different from those of bulk samples, experimental characterization in this field is still limited, especially for magnetism. Recent studies have revealed that bulk misfit layer compounds (MLCs) with (LaSe)1.14(NbSe2)n = 1,2 exhibit an Ising superconductivity similar to that of heavily electron‐doped NbSe2 monolayers. This offers an opportunity to study the effect of SOC on the magnetism of 2D TMDs. Here, the possible SOC effect in (LaSe)1.14(NbSe2) is investigated by measuring nuclear magnetic resonance (NMR) and electrical transport. It is found that the LaSe layer not only functions as a charge reservoir for transferring electrons into the NbSe2 layer but also remarkably influences the local electronic environment around the 93Nb nuclei. More importantly, the significant SOC induces both a weak antilocalization (WAL) effect and anisotropic spin fluctuations in noncentrosymmetric NbSe2 layers. The present work contributes to a deep understanding of the role of the SOC effect in 2D TMDs and supports MCLs as an intriguing platform for exploring exotic physical properties within the 2D limit. [ABSTRACT FROM AUTHOR]

The REAl(Si,Ge) (RE = rare earth) family, known to break both the inversion- and time-reversal symmetries, represents one of the most suitable platforms for investigating the interplay between correlated-electron phenomena and topologically nontrivial bands. Here, we report on systematic magnetic, transport, and muon-spin rotation and relaxation (uSR) measurements on (Nd,Sm)AlGe single crystals, which exhibit antiferromagnetic (AFM) transitions at TN = 6.1 and 5.9 K, respectively. In addition, NdAlGe undergoes also an incommensurate-to-commensurate ferrimagnetic transition at 4.5 K. Weak transverse-field µSR measurements confirm the AFM transitions, featuring a ∼90% magnetic volume fraction. Zero-field (ZF) µSR measurements reveal a more disordered internal field distribution in NdAlGe than in SmAlGe, reflected in a larger transverse muon-spin relaxation rate λT at T ≪ TN. This may be due to the complex magnetic structure of NdAlGe, which undergoes a series of metamagnetic transitions in an external magnetic field, while SmAlGe shows only a robust AFM order. In NdAlGe, the topological Hall effect (THE) appears between the first and the second metamagnetic transitions for H ∥ c, while it is absent in SmAlGe. Such THE in NdAlGe is most likely attributed to the field-induced topological spin textures. The longitudinal muon-spin relaxation rate λL, diverges near the AFM order, followed by a clear drop at T < TN. In the magnetically ordered state, spin fluctuations are significantly stronger in NdAlGe than in SmAlGe. In general, our longitudinal-field μSR data indicate vigorous spin fluctuations in NdAlGe, thus providing valuable insights into the origin of THE and of the possible topological spin textures in REAl(Si,Ge) Weyl semimetals. [ABSTRACT FROM AUTHOR]

We investigate strongly correlated solid solutions of Fe1 – xCoxSi with a disrupted B20 cubic structure. Within the framework of spin-fluctuation theory and a model of the density of electronic states derived from first-principles calculations using the generalized gradient approximation with the inclusion of strong Coulomb correlations (GGA + U), temperature transitions in Fe1 – xCoxSi alloys (illustrated with the examples of x = 0.2 and 0.3) with Dzyaloshinskii–Moriya interaction are examined. In the considered compounds, a "blurred" temperature-dependent first-order magnetic phase transition occurs, which is accompanied by a change in the sign of the intermode-coupling parameter in the Ginzburg–Landau functional. During such a transition, skyrmion A phases emerge within limited temperature ranges and external magnetic fields, beyond which experimentally observable fluctuations of the magnetic moments of spin spirals occur. The (h–T) diagrams are plotted, indicating regions of long-range order, and fluctuational and skyrmion phases. Fe1 – xCoxSi phases with x = 0.2 and 0.3 align well with experimental observations. [ABSTRACT FROM AUTHOR]

We study the dependence of magnetic properties: Curie temperature, mean and local magnetic moments—on the type of crystal lattice and average number of d electrons per atom. The problem is considered in two approximations: with spin fluctuations not taken into account, in the Stoner mean field theory, and with spin fluctuations taken into account, in the dynamic spin fluctuation theory (DSFT). In the DSFT, we obtain an analogue of the Slater–Pauling curve for the mean magnetic moment at finite temperatures. Numerical results in the DSFT are in qualitative agreement with experiment: with magnetic phase diagram and dependence of magnetic moment on concentration in ferromagnetic alloys. [ABSTRACT FROM AUTHOR]

The Many-body problem is very important issue in physics. Usually perturbation calculations based on the Green's function have been used to analyze such a problem, however, infinite orders of perturbation calculations are required to obtain exact solutions, thus resulting in the analytical and numerical difficulties. To overhaul such difficulties, we propose the new calculation method based on the differential forms, which are able to evaluate exact solutions if Hamiltonian is composed of Fermi particles. Since our proposed method is based on time evolution equations, comparisons with the calculations derived from Feynman Kernel is possible, with showing complete agreement. Furthermore we applied this method to the simplest Anderson Hamiltonian to investigate the appearance of magnetic moment. The calculation results show that magnetic moment easily disappears with small Coulomb repulsive energy, possibly implying the spin fluctuations. [ABSTRACT FROM AUTHOR]

The experimental data on low-temperature (T < 40 K) neutron scattering and electron paramagnetic resonance for a helical magnet manganese monosilicide (MnSi) are analyzed. It is established that the smooth evolution of the parameters of spin fluctuations considered both in the conventional theory of magnetic phase transitions and in its generalization to the case of helical magnets is disturbed by the presence of spin-fluctuation transitions (SFTs) in which the amplitude of spin fluctuations and their correlation radius change sharply. In a zero magnetic field, the transition at the temperature Tc = 29 K, which is usually interpreted as the transition to a helical magnetically ordered phase, is preceded by two spin-fluctuation transitions with T1 = 32 K and T2 = 30.5 K. In a magnetic field of B ~ 2 T at a temperature of 29 K coinciding with Tc, another spin-fluctuation transition with the parameters characteristic for the SFT inside the magnetically ordered phase is discovered. It is shown that, as the temperature decreases, MnSi at T = T1 undergoes the SFT with the appearance of helical fluctuations, while the appearance of a helical phase (B = 0) or a spin-polarized phase (B = 2 T) occurs at T = T2 and is accompanied by a spin-fluctuation transition. [ABSTRACT FROM AUTHOR]

We study paramagnetic characteristics of ferromagnetic metals near the Curie temperature T C using the dynamic spin fluctuation theory. In contrast with most first-principles calculations, our results for the uniform paramagnetic susceptibility show a clear deviation from the Curie–Weiss law. We demonstrate that the susceptibility and correlation radius have the power-law behavior at temperatures up to 1.1–1.15 T C , which gives an estimate for the region of critical temperatures in metals. Our theoretical critical exponents for Fe, Co, and Ni are in reasonable agreement with the low-field susceptibility measurements and neutron scattering experiments. • Paramagnetic properties of 3d metals near Curie point were studied in the DSFT. • Temperature dependence of susceptibility and correlation radius were derived. • Critical exponents of susceptibility and correlation radius were calculated. • The results are in agreement with bulk measurements and critical scattering. • The region of critical temperatures in metals extends up to 1.1-1.15 Tc. [ABSTRACT FROM AUTHOR]

The itinerant ferromagnetism is reported in A2T12P7 (A = lanthanoid, Group 2-4 element, T = transition metal) with Zr2Fe12P7-type structure. In order to investigate the behavior of electrons in this structure, we have synthesized single crystals of (Ca1-xMgx)2Co12P7 and measured magnetizations. From magnetic susceptibility, we found that Ca2Co12P7 shows a ferromagnetic transition at TC = 78 K, which is attributed to the Co-3d itinerant electrons. We also found the Curie temperature decreases and eventually disappears around x~0.6, when Ca is substituted by Mg. It has been suggested that the electronic density of states changes and the magnetic state of this system crosses the quantum critical point due to the positive chemical-pressure effect of the Ca substitution by Mg [ABSTRACT FROM AUTHOR]

Nematicity, which refers to a phase of broken rotational but preserved translational symmetry, is underlined by the appearance of anisotropic properties and leaves remarkable fingerprints in all measurable physical quantities upon crossing the structural tetragonal-orthorhombic transition at Ts in several iron-based materials. Here, we review part of our own broadband optical investigations, addressing the impact of nematicity on the charge dynamics, as a function of temperature and of tunable applied stress, the latter acting as an external symmetry breaking field. We shall first focus our attention on FeSe, which undergoes a nematic (structural) transition without any subsequent onset of magnetic ordering below Ts. FeSe thus provides an opportunity to study nematicity without the limitations due to the reconstruction of the Fermi surface because of the spin-density-wave collective state in the orthorhombic phase, typical for several other iron-based superconductors. Our data reveal an astonishing anisotropy of the optical response in the mid-infrared-to-visible spectral range, which bears testimony of an important polarization of the underlying electronic structure in agreement with angle-resolved-photoemission-spectroscopy results. Our findings at high energy scales support models for the nematic phase resting on an orbital-ordering mechanism, supplemented by orbital selective band renormalization. The optical results at energies close to the Fermi level furthermore emphasize scenarios relying on scattering by anisotropic spin-fluctuations and shed new light on the origin of nematicity in FeSe. Moreover, the composition at which the associated Weiss temperature of the nematic susceptibility extrapolates to zero is found to be close to optimal doping (i.e., in coincidence with the largest superconducting transition temperature), boosting the debate to what extent nematic fluctuations contribute to the pairing-mechanism and generally affect the electronic structure of iron-based superconductors. The present review then offers a discussion of our optical data on the optimally hole-doped Ba0.6K0.4Fe2As2. We show that the stress-induced optical anisotropy in the infrared spectral range is reversible upon sweeping the applied stress and occurs only below the superconducting transition temperature. These findings demonstrate that there is a large electronic nematicity at optimal doping which extends right under the superconducting dome.

There has been controversy about the driving force of the nematic order in the FeSe superconductor. Here, we present a detailed study of the 57 Fe Mössbauer spectra of FeSe single-crystal powders, focusing on the temperature dependences of the hyperfine parameters in the vicinity of the nematic transition temperature, T s ∼ 90 K. The nematicity-induced splitting of d xz and d and the establishing way of the associated nematic correlations. Analysis of the linewidths shows that spin fluctuations occur not only below 70 K but also across yz bands, obtained from the anomalous increase in quadrupole splitting near T s , starts at 143 K. The temperature evolution of the lattice dynamics, deduced from the recoilless fractions and second-order Doppler shifts, is found to undergo successively two segments of phonon-softening (160 K-105 K) and phonon-hardening (105 K-90 K), related to the appearance of local orthorhombic distortions above T s and the establishing way of the associated nematic correlations. Analysis of the linewidths shows that spin fluctuations occur not only below 70 K but also across T s (105 K-70 K), accompanied by the non-Fermi liquid behavior of the electrons. The results demonstrate the strong interactions between lattice, spin, and electron degrees of freedom in the vicinity of T s and that the lattice degrees of freedom may play an essential role in driving the nematic order for FeSe., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

The magnetocaloric effect (MCE) in La _1− _z R _z (Fe _0.89− _x Mn _x Si _0.11 ) _13 H _y _max (R = Ce and Pr) is verified in view of correlation between alloying recipes such as selection of doping elements and fundamental physics that governs MCE. The Ce-doped specimen with z = 0.3 & x = 0.017 exhibits a peaky isothermal entropy change Δ S _M profile with a maximum value of 20 J kg ^−1 K under a field change of 0.8 T at the Curie temperature of 285 K. In contrast, the enlarged field dependence of the Curie temperature and diminished hysteresis results in the adiabatic temperature change Δ T _ad of 2.7 K under a field change of 0.8 T at the Curie temperature of 289 K for the Pr-doped specimen.

Antiferromagnetic fluctuations are believed to be a promising glue to drive high-temperature superconductivity especially in cuprates. Here, we perform a close inspection of the superconducting mechanism from spin fluctuations in the Eliashberg framework by employing a typical one-band model on a square lattice. While spin fluctuations can eventually drive superconductivity as is well established, we find that the superconducting tendency is suppressed substantially by a seemingly negligible contribution from a small momentum transfer far away from $(\pi,\pi)$ . This suppression comes from phase frustration of the pairing gap and is expected to be a general feature due to the repulsive pairing interaction of spin fluctuations. Furthermore, we find that the momentum dependence of the pairing gap largely deviates from the functional form of $\cos k_{x} - \cos k_{y}$ , although this form is well established in cuprate superconductors. We argue that an instantaneous magnetic interaction plays the important role to understand high-critical temperature of superconductivity as well as the momentum dependence of the pairing gap.

We theoretically and numerically investigate the spin fluctuations induced in a thermal atomic ensemble by an external fluctuating uniaxial magnetic field, in the context of a standard spin noise spectroscopy (SNS) experiment. We show that additional spin noise is excited, which dramatically depends on the magnetic noise variance and bandwidth, as well as on the power of the probe light and its polarization direction. We develop an analytical perturbative model proving that this spin noise first emerges from the residual optical pumping in the medium, which is then converted into spin fluctuations by the magnetic noise and eventually detected using SNS. The system studied is a spin-1 system, which thus shows both Faraday rotation and ellipticity noises induced by the random magnetic fluctuations. The analytical model gives results in perfect agreement with the numerical simulations, with potential applications in future experimental characterization of stray field properties and their influence on spin dynamics.

Advanced experimental measurements are crucial for driving theoretical developments and unveiling novel phenomena in condensed matter and materials physics, which often suffer from the scarcity of large-scale facility resources, such as x-ray or neutron scattering centers. To address these limitations, we introduce a methodology that leverages the Bayesian optimal experimental design paradigm to efficiently uncover key quantum spin fluctuation parameters from x-ray photon fluctuation spectroscopy (XPFS) data. Our method is compatible with existing theoretical simulation pipelines and can also be used in combination with fast machine learning surrogate models in the event that real-time simulations are unfeasible. Our numerical benchmarks demonstrate the superior performance in predicting model parameters and in delivering more informative measurements within limited experimental time. Our method can be adapted to many different types of experiments beyond XPFS and spin fluctuation studies, facilitating more efficient data collection and accelerating scientific discoveries.

Understanding the normal electronic state is crucial for unveiling the mechanism of unconventional superconductivity (SC). In this paper, by applying a magnetic field of up to 37 T on FeSe single crystals, we could reveal the normal-state transport properties after SC was completely suppressed. The normal-state resistivity exhibited a Fermi liquid behavior at low temperatures. Large orbital magnetoresistance (MR) was observed in the nematic state with H//c, whereas MR was negligible with H//ab. The magnitude of the orbital MR showed an unusual reduction, and Kohler’s rule was severely violated below 10–25 K; these were attributable to spin fluctuations. The results indicated that spin fluctuations played a paramount role in the normalstate transport properties of FeSe albeit the Fermi liquid nature was at low temperature. [ABSTRACT FROM AUTHOR]

We have studied the high-pressure magnetic property in UGe 2 where ferromagnetic superconductivity appears under high pressure. In this study, we focus on the magnetic property at pressures above the ferromagnetic critical pressure P c =1.6 GPa. The temperature and magnetic field dependences of the dc-magnetization have been measured under high pressures up to 5.1 GPa by using a ceramic anvil high pressure cell. At pressures above P c , the magnetic susceptibility x shows a broad maximum around T χmax and the magnetization at 2.0 K shows an abrupt increase (metamagnetic transition) at H c . With increasing pressure, the peak structure in x becomes broader, and the peak position T χmax moves to the higher temperature region. The metamagnetic field H c increases rapidly with increasing pressure. At pressures above 4.1 GPa, x shows a simple temperature dependence, and the magnetization increases linearly with increasing field. These phenomena in UGe 2 resemble to those in the intermetallic compounds of 3d transition metals such as Co(S 1-x Se x ) and YCo 2 . We discuss the experimental results by using the phenomenological spin-fluctuation theory. © 2013 The Korean Physical Society.

We have studied the high-pressure magnetic property in UGe 2 where ferromagnetic superconductivity appears under high pressure. In this study, we focus on the magnetic property at pressures above the ferromagnetic critical pressure P c =1.6 GPa. The temperature and magnetic field dependences of the dc-magnetization have been measured under high pressures up to 5.1 GPa by using a ceramic anvil high pressure cell. At pressures above P c , the magnetic susceptibility x shows a broad maximum around T χmax and the magnetization at 2.0 K shows an abrupt increase (metamagnetic transition) at H c . With increasing pressure, the peak structure in x becomes broader, and the peak position T χmax moves to the higher temperature region. The metamagnetic field H c increases rapidly with increasing pressure. At pressures above 4.1 GPa, x shows a simple temperature dependence, and the magnetization increases linearly with increasing field. These phenomena in UGe 2 resemble to those in the intermetallic compounds of 3d transition metals such as Co(S 1-x Se x ) and YCo 2 . We discuss the experimental results by using the phenomenological spin-fluctuation theory. © 2013 The Korean Physical Society.

Magnetic, magnetocaloric, and magnetoresistance properties of polycrystalline Tb2Ni0.94Si3.2 alloy have been investigated. Magnetic susceptibilities (AC and DC), remanent magnetization and the heat capacity studies of Tb2Ni0.94Si3.2 provide evidence for the spin glass behavior below the temperature, Tf = 5.2 K. At the Néel temperature, TN = 12.7 K, Tb2Ni0.94Si3.2 alloy orders antiferromagnetically. The presence of metamagnetic transition is observed in isothermal magnetization and magnetoresistance studies. Also, a magnetoresistance of 22% is exhibited by the alloy at temperature T = 4 K in an applied magnetic field of 9 T. A magnetic entropy change of 12 J/kg K with the relative cooling power of 504 J/kg for a magnetic field change of 9 T is observed in the studied alloy. Influence of spin fluctuations and short-range ferromagnetic correlations is reflected in magnetoresistance and relative cooling power. The magnetic and magnetoresistance properties make this alloy as a good magnetocaloric material with moderate magnetoresistance. [ABSTRACT FROM AUTHOR]

We present the results of an experimental study focused around CeNi5 in the CexGd1-xNi5 system. Pseudobinary bulk samples were prepared with concentration of x = 0:85, 0.9, 0.95, and 0.97 by arc melting method. The structural analysis confirmed the CaCu5 hexagonal crystal structure with P6/mmm space group and proved the existence of a single phase in all of them. The measurement of the magnetic properties shows that the increase of the Ce content leads to lower TC values. Above x = 0:9 spin fluctuations behaviour appears with a shoulder in M(T) around T = 130 K. Heat capacity measurements support these observations. [ABSTRACT FROM AUTHOR]

We perform spin noise spectroscopy experiments in metastable helium atoms at room temperature, with a probe light whose frequency is blue detuned from the D _0 line. Both circular birefringence fluctuations (Faraday noise) and linear birefringence fluctuations (ellipticity noise) are explored theoretically and experimentally. In particular, it is shown that in both cases but for different optical detunings, two noise resonances are isolated at the Larmor frequency and at twice the Larmor frequency with a behavior, which strongly depends on the orientation of the probe field polarization. The simple structure of metastable helium allows us to probe, model and explain the changes in the behavior of these peaks in terms of circular and linear dichroisms and birefringences as well as in terms of spin oscillation modes.

Recently synthesized Kagome compounds AV _3 Sb _5 attract great attention due to the unusual coexistence of the topology, charge density wave, and superconductivity. In this work, based on the band structures for CsV _3 Sb _5 in the pristine phase, we construct an effective six-band model for the low-energy processes; utilizing the random phase approximation on the effective six-band model, we show that the $E_{1u}$ ( p wave) pairing dominates in the region of $0\lt U\lt0.32$ eV, the $A_{2g}$ ( I wave) in the region of $0.32\lt U\lt0.75$ eV and the $E_{2g}$ ( d wave) in the region of $0.75\lt U\lt1$ eV. Considering that the correlation in AV _3 Sb _5 is weak or intermediate, these results suggest that pairing symmetry is $A_{2g}$ ( I -wave) in the CsV _3 Sb _5 , which can explain some recent experiments about pairing symmetry.

The rare-earth magnetism in the intermetallic compound Yb0.5Ce0.5Ni5 was studied using X-ray diffraction, magnetization, heat capacity, and electrical resistivity measurements. The effect of spin fluctuations (SF) was observed in M(T) at ~40 K. The measurement of thermal and transport properties supported the results obtained from magnetic measurements. Collected experimental data showed that Yb/Ce substitution shifts the maximum temperature for spin fluctuations to a lower temperature compared to that for pure CeNi5. Moreover, at low temperatures, an anomaly in the heat capacity of possible magnetic origin arising from Yb3+ was detected. Ce atoms seemed to remain in a non-magnetic valence state at almost 4+.

We propose a numerical continuation method for a nonlinear system that consists of scalar and functional equations. At each parameter step, we solve the system by a modified Gauss–Seidel method. An advantage of this method is that the system is divided into two parts and each part is solved by a suitable numerical method with a desired precision. We solve the functional equations self-consistently at each step of the iteration process for the system of scalar equations. We apply the proposed method for calculating temperature dependence of magnetic characteristics of metals in the dynamic spin-fluctuation theory. [ABSTRACT FROM AUTHOR]

The brief history of itinerant-electron magnetism has been reviewed in terms of spin fluctuations. In the research field of itinerant-electron magnetism, the effects of spin fluctuations are very important to understand the experimental results. Among itinerant-electron theories, the self-consistent renormalization theory of spin fluctuations (the SCR theory) has developed since 1973 by Moriya’s group. Now, we can use the SCR theory in order to analyze our experimental data quantitatively by means of 4 spin fluctuation parameters, ps, F1, T0, TA, by which we can calculate Curie temperature TC, inverse magnetic susceptibility 1/χ, nuclear spin-lattice relaxation rate 1/T1, specific heats C, etc. quantitatively. In fact, the quantitative discussion is very important to characterize itinerant-electron magnets which distribute from weak-itinerant to localized-moment regimes. Furthermore, Takahashi’s theory of spin fluctuations has been developed since 1986 by setting up two hypotheses in order to solve some serious problems existing in previous itinerant theories including the SCR theory. One is that total amplitudes of spin fluctuations should be conserved (TAC). The second is global consistency (GC), implying that the continuity of magnetization and inverse magnetic susceptibility should be preserved through TC. These two assumptions result in two equations among these 4 spin-fluctuation parameters, by which we can estimate 4 parameters quite easily only by using static magnetic measurements like magnetization and magnetic susceptibility. At the same time, the assumption TAC may result in the unified picture of itinerant ferromagnetism. The effects of spin fluctuations are also important to understand the exotic superconductors of which mechanism is not of BCS-type but of magnetic origin. The superconducting transition temperatures TC of those exotic superconductors can be explained universally by T0 which is the energy width of the spin-fluctuation spectrum. Here, the effects of spin fluctuations are explained quantitatively in itinerant-electron magnetism as well as exotic superconductivity in the review. [ABSTRACT FROM AUTHOR]

The magnetic structure of polymorphic Cr-Co-Ni medium entropy alloys is investigated as a function of temperature and chemical composition by ab initio calculations. Besides the thermal lattice expansion, the longitudinal spin fluctuations (LSFs) are accounted for in determining the magnetic state at finite temperature. We show that sizable local magnetic moments persist on all alloy components in the paramagnetic state for both face-centered cubic and hexagonal close-packed structures, and each alloy species exhibits particular temperature and concentration dependencies. The crucial role of LSFs for the finite temperature magnetic state and its impact on the temperature dependent elastic parameters are demonstrated. Unlabelled Image [ABSTRACT FROM AUTHOR]

An universal line revealing an independence of spin fluctuation contributions to the heat capacity on impurity content and its nature is discovered in the helical phase of Mn(Co,Fe)Si. This situation declares an invariance of the heat capacity of spin subsystem under doping, which probably arises as a result of relative stiffness of the helical spin structure in respect to the impurity spins. On the other hand the situation drastically changes at the helical fluctuation region when no long range spin order exists. At low temperatures the spin fluctuation contributions to the heat capacity for a whole set of compositions of Mn(Co,Fe)Si are described by a single power expression with an exponent less then unity, which implies divergence of the ratio C p / T at T → 0. The current data are revealing that a singular quantum critical point does not exist in the system under study. In its place, one can see some sort of a quantum critical cloud covering a significant range of dopant concentrations. • The helical magnet MnSi has played a special role in efforts of investigations of quantum criticality phenomena. • We used so-called "chemical" pressure technique • Mysterious universal line of spin fluctuation heat capacity of Mn(Fe,Co)Si was found. • The latter shows that a singular quantum critical point does not exist in the system under study. • Instead, one can see a sort of quantum critical cloud covering a range of dopant concentrations. [ABSTRACT FROM AUTHOR]

Abstract The finite temperature elastic properties of the equiatomic CoCrFeNi medium-entropy alloy has been studied by density functional theory. Besides atomic vibrations and electronic free energy, the predictive model developed here includes contributions from spin fluctuations (SFs) in determining the elastic properties of CoCrFeNi. Including SFs changes the magnitude of the temperature derivatives of the poly-crystal elastic moduli, resulting in a close agreement between simulation and experimentally measured trends. How the single-crystal elastic moduli depend on SFs and how these dependencies influence changes in the poly-crystal elastic moduli are analyzed systematically. Finally, the elemental sources to the simulated trends are identified. Graphical Abstract [ABSTRACT FROM AUTHOR]

Using an efficient first-principles computational scheme, we calculate the intrinsic stacking fault energy ( γ i s f ) and the unstable stacking fault energy ( γ u s f ) of paramagnetic γ -Fe as a function of temperature. The formation energies are derived from free energies accounting for thermal longitudinal spin fluctuations (LSFs). LSFs are demonstrated to be important for the accurate description of the temperature-dependent magnetism, intrinsic and unstable stacking fault energies, and have a comparatively large effect on γ i s f of γ -Fe. Dominated by the magneto-volume coupling at thermal excitations, γ i s f of γ -Fe exhibits a positive correlation with temperature, while γ u s f declines with increasing temperature. The predicted stacking fault energy of γ -Fe is negative at static condition, crosses zero around 540 K, and reaches 71.0 mJ m −2  at 1373 K, which is in good agreement with the experimental value. According to the plasticity theory formulated in terms of the intrinsic and unstable stacking fault energies, twinning remains a possible deformation mode even at elevated temperatures. Both the large positive temperature slope of γ i s f and the predicted high-temperature twinning are observed in the case of austenitic stainless steels. [ABSTRACT FROM AUTHOR]

57 Fe Mössbauer spectra were measured at different temperatures between 5.9 K and 300 K on the recently discovered self-doped superconducting RbGd 2 Fe 4 As 4 O 2 with T c as high as 35 K. Singlet pattern was observed down to the lowest temperature measured in this work, indicating the absence of static magnetic order on the Fe site. The intermediate isomer shift in comparison with that of the samples RbFe 2 As 2 and GdFeAsO confirms the self doping induced local electronic structure change. Surprisingly, we observe two magnetic fluctuation induced spectral broadenings below  ∼ 15 K and  ∼ 100 K which are believed to be originated from the transferred magnetic fluctuations of the Gd 3 + moments and that of the magnetic fluctuations of the Fe atoms, respectively. [ABSTRACT FROM AUTHOR]

The effect of spin fluctuations on the heat capacity and homogeneous magnetic susceptibility of the chiral magnetic MnSi in the vicinity of magnetic transition has been investigated by using the free energy functional of the coupled electron and spin subsystems and taking into account the Dzyaloshinsky-Moriya interaction. For helical ferromagnetic ordering, we found that zero-point fluctuations of the spin density are large and comparable with fluctuations of the non-uniform magnetization. The amplitude of zero-point spin fluctuations shows a sharp decrease in the region of the magnetic phase transition. It is shown that sharp decrease of the amplitude of the quantum spin fluctuations results in the lambda-like maxima of the heat capacity and the homogeneous magnetic susceptibility. Above the temperature of the lambda anomaly, the spin correlation radius becomes less than the period of the helical structure and chiral fluctuations of the local magnetization appear. It is shown that formation of a "shoulder" on the temperature dependence of the heat capacity is due to disappearance of the local magnetization. Our finding allows to explain the experimentally observed features of the magnetic phase transition of MnSi as a result of the crossover of quantum and thermodynamic phase transitions. [ABSTRACT FROM AUTHOR]