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The magnetic and transport characteristics of substitutional solid solutions of the Tm1− xYb xB12 rare earth dodecaborides have been investigated. The measurements performed in the wide temperature range 1.8−300 K on the high-quality single-crystalline samples make it possible to conclude that as x increases, antiferromagnetic instability develops with the quantum critical point ( T N = 0) near x = 0.3 and relevant dielectrization of the electron structure in the range 0 ≤ x ≤ 0.8 takes place. With the results of the thermoelectric measurements in Tm1− xYb xB12, the activation energy values and their dependence on x have been determined. [ABSTRACT FROM AUTHOR]

The magnetoresistance and magnetization of single-crystal samples of rare-earth dodecaborides RB12 (R = Ho, Er, Tm, Lu) have been measured at low temperatures (1.8–35 K) in a magnetic field of up to 70 kOe. The effect of positive magnetoresistance that obeys the Kohler’s rule Δρ/ρ = f(ρ(0, 300 K) H/ρ(0, T)) is observed for the nonmagnetic metal LuB12. In the magnetic dodecaborides HoB12, ErB12, and TmB12, three characteristic regimes of the magnetoresistance behavior have been revealed: the positive magnetoresistance effect similar to the case of LuB12 is observed at T > 25 K; in the range T N ≤ T ≤ 15 K, the magnetoresistance becomes negative and depends quadratically on the external magnetic field; and, finally, upon the transition to the antiferromagnetic phase ( T < T N), the positive magnetoresistance is again observed and its amplitude reaches 150% for HoB12. It has been shown that the observed anomalies of negative magnetoresistance in the paramagnetic phase can be explained within the Yosida model of conduction electron scattering by localized magnetic moments. The performed analysis confirms the formation of spin-polaron states in the 5 d band in the vicinity of rare-earth ions in paramagnetic and magnetically ordered phases of RB12 and makes it possible to reveal a number of specific features in the transformation of the magnetic structure of the compounds under investigation. [ABSTRACT FROM AUTHOR]

The angular dependences of the magnetization and Hall resistance have been investigated by the method of the sample rotation in the magnetic field in the high-quality single-crystal samples in the paramagnetic and magnetically ordered phases of CeB6 in the magnetic field up to 60 kOe. It has been shown that, as CeB6 undergoes the transition from the antiferromagnetic modulated phase to the so-called antiferroquadrupolar phase, the easy-magnetization axis in the [110] plane changes from 〈100〉 to 〈110〉. The magnetic field dependences of the anisotropic component of the magnetization differ radically in these magnetically ordered phases. The analysis provides evidence in favor of the formation of a state with the spin density wave (SDW phase) in the temperature range TN ≈ 2.3 K < T < TQ ≈ 3.3 K in CeB6. [ABSTRACT FROM AUTHOR]

The angular dependences of the magnetization and Hall resistance have been investigated by the method of the sample rotation in the magnetic field in the high-quality single-crystal samples in the paramagnetic and magnetically ordered phases of CeB6 in the magnetic field up to 60 kOe. It has been shown that, as CeB6 undergoes the transition from the antiferromagnetic modulated phase to the so-called antiferroquadrupolar phase, the easy-magnetization axis in the [110] plane changes from 〈100〉 to 〈110〉. The magnetic field dependences of the anisotropic component of the magnetization differ radically in these magnetically ordered phases. The analysis provides evidence in favor of the formation of a state with the spin density wave (SDW phase) in the temperature range TN ≈ 2.3 K < T < TQ ≈ 3.3 K in CeB6. [ABSTRACT FROM AUTHOR]

High-precision measurements of thermopower have been performed in a wide temperature range (2–300 K) for a series of cerium-based heavy-fermion compounds, including CeB6, CeAl3, CeCu6, and substitutional solid solutions of the CeCu6 − x Au x system ( x = 0.1, 0.2). All compounds exhibit an unusual (logarithmic) asymptotic behavior of the temperature dependence of the Seebeck coefficient: S ∝ −ln T. In the case of cerium hexaboride, this anomalous behavior of S( T) is accompanied by the appearance of weak-carrier-localization-mode asymptotics in the conductivity (σ( T) ∝ T 0.39), while the paramagnetic susceptibility χ( T) and the effective mass of charge carriers m eff( T) vary according to a power law (χ( T), m eff( T) ∝ T −0.8) in the temperature interval T = 10–80 K. This behavior corresponds to renormalization of the density of states at the Fermi level. The observed anomalous behavior of thermopower in CeB6 and other cerium-based intermetallic compounds is attributed to the formation of heavy fermions (many-body states in the metal matrix) at low temperatures. [ABSTRACT FROM AUTHOR]

The influence of substitution on the binding energy of many-body states and the formation of the magnetically ordered state in a heavy-fermion compound (CeAl2) have been studied by measuring the transport characteristics (Hall effect, resistivity) in intermetallic compounds of the Ce(Al1− x M x )2 system (M = Ni, Co; x ≤ 0.08). It is established that the Hall coefficient R H in Ce(Al1− x Co x )2 intermetallides with x = 0.05 and 0.08 grows by more than an order of magnitude as the temperature decreases from 1.8 to 300 K. The experimental data are used to estimate the effective mass of charge carriers, the relaxation time, and the localization radius of many-body states. [ABSTRACT FROM AUTHOR]

High-precision measurements of thermopower have been performed in a wide temperature range (2–300 K) for a series of cerium-based heavy-fermion compounds, including CeB6, CeAl3, CeCu6, and substitutional solid solutions of the CeCu6 − x Au x system ( x = 0.1, 0.2). All compounds exhibit an unusual (logarithmic) asymptotic behavior of the temperature dependence of the Seebeck coefficient: S ∝ −ln T. In the case of cerium hexaboride, this anomalous behavior of S( T) is accompanied by the appearance of weak-carrier-localization-mode asymptotics in the conductivity (σ( T) ∝ T 0.39), while the paramagnetic susceptibility χ( T) and the effective mass of charge carriers m eff( T) vary according to a power law (χ( T), m eff( T) ∝ T −0.8) in the temperature interval T = 10–80 K. This behavior corresponds to renormalization of the density of states at the Fermi level. The observed anomalous behavior of thermopower in CeB6 and other cerium-based intermetallic compounds is attributed to the formation of heavy fermions (many-body states in the metal matrix) at low temperatures. [ABSTRACT FROM AUTHOR]

Precision measurements of transport and magnetic parameters of high-quality CeB6 single crystals are performed in the temperature range 1.8—300 K. It is shown that their resistivity in the temperature interval 5 K < T < T* ≈ 80 K obeys not a logarithmic law, which is typical of the Kondo mechanism of charge carrier scattering, but the law ρ ∝ T −1/η corresponding to the weak localization regime with a critical index 1/η = 0.39 ± 0.02. Instead of the Curie-Weiss dependences, the asymptotic form χ( T) ∝ T −0.8 is obtained for magnetic susceptibility of CeB6 in a temperature range of 15–300 K. Analysis of the field dependences of magnetization, magnetoresistance, and the Hall coefficient in the paramagnetic and magnetically ordered phases of CeB6 and comparison with the results of measurements of Seebeck coefficient, the inelastic neutron scattering coefficient, and EPR spectroscopy lead to the conclusion that the Kondo lattice model and skew scattering model cannot be used for describing the transport and thermodynamic parameters of this compound with strong electron correlations. On the basis of detailed analysis of experimental data, an alternative approach to interpreting the properties of CeB6 is proposed using (1) the assumption concerning itinerant paramagnetism and substantial renormalization of the density of electron states upon cooling in the vicinity of the Fermi energy, which is associated with the formation of heavy fermions (spin-polaron states) in the metallic CeB6 matrix in the vicinity of Ce sites; (2) the formation of ferromagnetic nanosize regions from spin polarons at 3.3 K < T < 7 K and a transition to a state with a spin density wave (SDW) at T Q ≈ 3.3 K; and (3) realization of a complex magnetic phase H-T diagram of CeB6, which is associated with an increase in the SDW amplitude and competition between the SDW and antiferromagnetism of localized magnetic moments of cerium ions. [ABSTRACT FROM AUTHOR]

The Hall coefficient RH , resistivity ρ, and Seebeck coefficient S of the CeAl2 compound with fast electron density fluctuations were studied in a wide temperature range (from 1.8 to 300 K). Detailed measurements of the angular dependences RH(φ, T, H ≤ 70 kOe) were performed to determine contributions to the anomalous Hall effect and study the behavior of the anomalous magnetic RHam and main RHa components of the Hall signal of this compound with strong electron correlation. The special features of the behavior of the anomalous magnetic component RHam were used to analyze the complex magnetic phase diagram H–T determined by magnetic ordering in the presence of strong spin fluctuations. An analysis of changes in the main contribution RHa(H, T) to the Hall effect made it possible to determine the complex activation behavior of this anomalous component in the CeAl2 intermetallic compound. The results led us to conclude that taking into account spin–polaron effects was necessary and that the Kondo lattice and skew-scattering models were of very limited applicability as methods for describing the low-temperature transport of charge carriers in cerium-based intermetallic compounds. The effective masses and localization radii of manybody states in the CeAl2 matrix were estimated to be (55–90)m0 and 6–10 Å, respectively. The behaviors of the parameters RH, S, and ρ were jointly analyzed. The results allowed us to consistently describe the transport coefficients of CeAl2 . © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The Hall coefficient RH , resistivity ρ, and Seebeck coefficient S of the CeAl2 compound with fast electron density fluctuations were studied in a wide temperature range (from 1.8 to 300 K). Detailed measurements of the angular dependences RH(φ, T, H ≤ 70 kOe) were performed to determine contributions to the anomalous Hall effect and study the behavior of the anomalous magnetic RHam and main RHa components of the Hall signal of this compound with strong electron correlation. The special features of the behavior of the anomalous magnetic component RHam were used to analyze the complex magnetic phase diagram H–T determined by magnetic ordering in the presence of strong spin fluctuations. An analysis of changes in the main contribution RHa(H, T) to the Hall effect made it possible to determine the complex activation behavior of this anomalous component in the CeAl2 intermetallic compound. The results led us to conclude that taking into account spin–polaron effects was necessary and that the Kondo lattice and skew-scattering models were of very limited applicability as methods for describing the low-temperature transport of charge carriers in cerium-based intermetallic compounds. The effective masses and localization radii of manybody states in the CeAl2 matrix were estimated to be (55–90)m0 and 6–10 Å, respectively. The behaviors of the parameters RH, S, and ρ were jointly analyzed. The results allowed us to consistently describe the transport coefficients of CeAl2 . © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Transition metal-based layered compounds with van der Waals gaps between the adjacent layers are a source of two-dimensional (2D) nanomaterials with nontrivial transport and magnetic properties. 2D ferromagnets, both metals and semiconductors, can be leveraged to produce spin-polarized current in spintronic devices with tailored functionalities. Here, we report on the synthesis, crystal growth, crystal and electronic structure, and magnetic properties of the Fe-based FeAl2S4 layered sulfide. In the crystal structure, Fe and Al atoms mix on octahedral and tetrahedral sites between hexagonal layers of S atoms, which are terminated by the van der Waals gaps. Band structure calculations reveal strong electronic correlations within the semiconducting ground state, which induce ferromagnetism with the magnetic moment of 0.12μB per formula unit for a Hubbard interaction U = 5 eV and Hund's rule coupling J = 0.8 eV. Crystal growth employing chemical vapor transport reactions results in bulk cleavable crystals, which show paramagnetic Curie–Weiss behavior at high temperatures with the Fe2+ magnetic centers. At low temperatures, an anomaly is observed on the magnetic susceptibility curve, below which the magnetization shows ferromagnetic hysteresis, indicating the presence of ferromagnetic correlations in FeAl2S4. [ABSTRACT FROM AUTHOR]

The galvanomagnetic and magnetic properties of EuB6 single crystal have been measured over wide temperature (1.8–300 K) and magnetic-field (up to 70 kOe) ranges, and the parameters of charge carriers and the characteristics of the magnetic subsystem are estimated in the paramagnetic and ferromagnetic ( T < T C ≈ 13.9 K) phases of this compound with strong electron correlations. In the temperature range T < T* ≈ 80 K, a magnetoresistance hysteresis Δρ( H)/ρ(0) is detected; it reaches a maximum amplitude of about 5% at T ≈ 12 K. The anomalies of charge transport observed in the temperature range T C < T < T* are shown to be related to the magnetic scattering of charge carriers ( m eff = (15–30) m 0, where m 0 is the free-electron mass) that results from a short-range magnetic order appearing upon the formation of ferromagnetic nanoregions (ferrons). [ABSTRACT FROM AUTHOR]

The galvanomagnetic and magnetic properties of EuB6 single crystal have been measured over wide temperature (1.8–300 K) and magnetic-field (up to 70 kOe) ranges, and the parameters of charge carriers and the characteristics of the magnetic subsystem are estimated in the paramagnetic and ferromagnetic ( T < T C ≈ 13.9 K) phases of this compound with strong electron correlations. In the temperature range T < T* ≈ 80 K, a magnetoresistance hysteresis Δρ( H)/ρ(0) is detected; it reaches a maximum amplitude of about 5% at T ≈ 12 K. The anomalies of charge transport observed in the temperature range T C < T < T* are shown to be related to the magnetic scattering of charge carriers ( m eff = (15–30) m 0, where m 0 is the free-electron mass) that results from a short-range magnetic order appearing upon the formation of ferromagnetic nanoregions (ferrons). [ABSTRACT FROM AUTHOR]

Randomness and frustration are believed to be two crucial criteria for the formation of spin glass state. However, the spin freezing occurs in some well-ordered crystals below the related temperature Tf due to the instability of each spin state, which induces the variation of either magnetic moment value or exchange energy. Here we explore the new mechanism of the in-site originated disorder in antiferromagnets Gd0.73La0.27B6 and GdB6, which is caused by the random mutual shifts of Gd3+ spins from the centrally symmetrical positions in the regular cubic lattice. The universal scaling of ESR linewidth temperature dependencies to the power law ΔH(T) ~ ((T − TD)/TD)α with α = − 1.1 ± 0.05 in the paramagnetic phase of both compounds demonstrates the identity of the origin of magnetic randomness. In Gd0.73La0.27B6 the resulting random spin configurations freeze at Tf ≈ 10.5 K where the maximum of magnetization is observed. Below Tf the splitting of ZFC and FC magnetization curves takes place as well as the magnetic state depends on the antecedent sample history. In the case of GdB6 the coherent displacement of Gd ions compete with these random shifts forming an antiferromagnetic (AFM) phase at TN = 15.5 K, which prevails over the spin freezing at Tf ≈ 13 K, expected from the ESR data. The observation of the hysteresis of the ESR spectrum in the AFM phase suggests that its properties may be determined by the competition of two types of AFM orders, which results in formation of stable magnetic domains with nonequivalent positions of AFM Gd pairs at T < 10 K. [ABSTRACT FROM AUTHOR]

Electron spin resonance (ESR) in strongly correlated metals is an exciting phenomenon, as strong spin fluctuations in this class of materials broaden extremely the absorption line below the detection limit. In this respect, ESR observation in CeB6 provides a unique chance to inspect Ce3+ magnetic state in the antiferroquadrupole (AFQ) phase. We apply the original high frequency (60 GHz) experimental technique to extract the temperature and angular dependences of g-factor, line width and oscillating magnetization. Experimental data show unambiguously that the modern ESR theory in the AFQ phase considering the Γ8 ground state of Ce3+ ion completely fails to predict both the g-factor magnitude and its angular dependence. Alignment of the external magnetic field along [100] axis induces a strong (more than twofold) broadening of ESR line width with respect to the other crystallographic directions and results also in the anomalous temperature dependences of the g-factor and oscillating magnetization. In this experimental geometry the latter parameter surprisingly exceeds total static magnetization by 20% at T* ~ 2.5 K. We argue that the unusual physical picture of ESR in CeB6 may be strongly affected by spin fluctuations and dynamic collective effects predominantly pronounced in [100] direction. [ABSTRACT FROM AUTHOR]

The antiferromagnetic ground state has been studied by transverse magnetoresistance, heat capacity and magnetization measurements, which were carried out on high quality single crystals of Tm0:996Yb0:004B12 dodecaboride in strong magnetic fields at liquid helium temperatures. Both antiferromagnetic-paramagnetic (AFP) and spin-orientation (AF1-AF2) phase transitions have been observed, and allowed to construct a complicated magnetic H-T phase diagram for this compound. Strong magnetoresistance anisotropy was found both in AF states (ρ(H∥[110])/ρ(H∥[111]) ~ 1:2 at H ~ 20 kOe) and at the critical field of AF-P transition (HN[100]/HN[111] ~ 1:25) in this magnetic metal with a simple fcc crystal structure. [ABSTRACT FROM AUTHOR]

The antiferromagnetic ground state has been studied by transverse magnetoresistance, heat capacity and magnetization measurements, which were carried out on high quality single crystals of Tm0.996Yb0.004B12 do-decaboride in strong magnetic fields at liquid helium temperatures. Both antiferromagnetic-paramagnetic (AF-P) and spin-orientation (AF1-AF2) phase transitions have been observed, and allowed to construct a complicated magnetic H-T phase diagram for this compound. Strong magnetoresistance anisotropy was found both in AF states (p(H∣∣[110])/p(H∣∣[111]) ~ 1:2 at H ~ 20 kOe) and at the critical field of AF-P transition (HN[100]/HN[111] ~ 1:25) in this magnetic metal with a simple fcc crystal structure. [ABSTRACT FROM AUTHOR]

Magnetic field dependences of the Hall coefficient RH and resistivity have been studied in detail for dilute magnetic compounds La1-xCexB6 (x ≤ 0.1) at temperatures 1.8-300 K. It was established that the regime of weak localization of charge carriers, which was observed in these heavy fermion systems below 30 K destroys gradually in magnetic field up to 8 T. Moreover, in addition to the strong negative magnetoresistance (Δ ρ/ρ ≈ 80%) a drastic enhancement of the negative Hall coefficient in magnetic field (Δ RH/RH ≈ 50%) has been deduced at liquid helium temperatures. The results of comprehensive analysis contradict the predictions of Kondo-impurity approach for this archetypal strongly correlated electron system in the dilute impurity limit. An alternative interpretation of La1-xCexB6 properties is developed on the basis of spin-polaron approach, Pauli paramagnetism and the density of states renormalization effects at low temperatures. [ABSTRACT FROM AUTHOR]

In the system Tm1-xYbxB12 the specific heat has been studied in a wide range of Yb-concentration in the vicinity of the quantum critical point xC ≈ 0.3. The results were obtained on high quality single crystalline samples of Tm0.7Yb0.3B12 compound placed near quantum critical point, both for antiferromagnetic metals (x < xC) as well as for paramagnetic insulators (x > xC) within a wide temperature range of 1.9-300 K in magnetic field up to 9 T. The temperature dependence of the magnetic contribution to specific heat for Tm0.74Yb0.26B12 shows a logarithmic divergence of the form: Cmag/T∿-lnT at T<4 K, which may be attributed to the quantum critical regime, and it is suppressed by strong external magnetic field. The Schottky anomaly of the magnetic contribution to specific heat in Tm1-xYbxB12 has been established and analyzed in detail. [ABSTRACT FROM AUTHOR]

A detailed study of charge transport in the paramagnetic phase of the cage-cluster dodecaboride Ho0.8Lu0.2B12 with an instability both of the fcc lattice (cooperative Jahn–Teller effect) and the electronic structure (dynamic charge stripes) was carried out at temperatures 1.9–300 K in magnetic fields up to 80 kOe. Four mono-domain single crystals of Ho0.8Lu0.2B12 samples with different crystal axis orientation were investigated in order to establish the singularities of Hall effect, which develop due to (i) the electronic phase separation (stripes) and (ii) formation of the disordered cage-glass state below T*~60 K. It was demonstrated that a considerable intrinsic anisotropic positive component ρanxy appears at low temperatures in addition to the ordinary negative Hall resistivity contribution in magnetic fields above 40 kOe applied along the [001] and [110] axes. A relation between anomalous components of the resistivity tensor ρanxy~ρanxx1.7 was found for H||[001] below T*~60 K, and a power law ρanxy~ρanxx0.83 for the orientation H||[110] at temperatures T < TS~15 K. It is argued that below characteristic temperature TS~15 K the anomalous odd ρanxy(T) and even ρanxx(T) parts of the resistivity tensor may be interpreted in terms of formation of long chains in the filamentary structure of fluctuating charges (stripes). We assume that these ρanxy(H||[001]) and ρanxy(H||[110]) components represent the intrinsic (Berry phase contribution) and extrinsic (skew scattering) mechanism, respectively. Apart from them, an additional ferromagnetic contribution to both isotropic and anisotropic components in the Hall signal was registered and attributed to the effect of magnetic polarization of 5d states (ferromagnetic nano-domains) in the conduction band of Ho0.8Lu0.2B12. [ABSTRACT FROM AUTHOR]

We report the study of transport and magnetic properties of the YbB6- δsingle crystals grown by inductive zone melting. A strong disparity in the low temperature resistivity, Seebeck and Hall coefficients is established for the samples with the different level of boron deficiency. The effective parameters of the charge transport in YbB6- δ are shown to depend on the concentration of intrinsic defects, which is estimated to range from 0.09% to 0.6%. The pronounced variation of Hall mobility μH found for bulk holes is induced by the decrease of transport relaxation time from τ ≈ 7.7 fs for YbB5.994 to τ ≈ 2.2 fs for YbB5.96. An extra contribution to conductivity from electrons with μH≈ -1000 cm2 V-1 s-1 and the very low concentration n / nYb≈ 10-6 discovered below 20 K for all the single crystals under investigation is suggested to arise from the surface electron states appeared in the inversion layer due to the band bending. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The transport and magnetic properties of single crystal samples of substitutional solid solutions EuCaB (0 ≤ x ≤ 0.26) have been studied at temperatures 1.8-300 K in magnetic fields up to 80 kOe. It has been shown that an increase in the calcium concentration results in the suppression of the charge transport accompanied by an increase in the amplitude of the colossal magnetoresistance (CMR) up to the value (ρ(0) − ρ( H))/ρ( H) ≈ 7 × 10 detected for x = 0.26 at liquid-helium temperature in a field of 80 kOe. The transition from the hole-like conductivity to the electron-like conductivity has been observed in the EuCaB solid solution in the CMR regime at T < 40 K. The Hall mobility values μH = 200−350 cm/(V s) estimated for charge carriers in the strongly disordered matrix of the EuCaB solid solution are comparable with the charge carrier mobility μH = 400−600 cm/(V s) for the undoped EuB compound. The anomalous behavior of the transport and magnetic parameters of the EuCaB solid solutions is discussed in terms of a metal-insulator transition predicted within the double exchange model for this system with low carrier density. [ABSTRACT FROM AUTHOR]

The galvanomagnetic properties of single-crystal samples with various isotopic boron compositions have been investigated for the first time for the normal state of superconductor LuB ( T c ≈ 0.44 K). Precision measurements of the resistivity, Hall coefficient, and magnetic susceptibility have been performed over a wide temperature range of 2-300 K in magnetic fields up to 80 kOe. A change of the charge transport regime in this nonmagnetic compound with metallic conduction is shown to occur near T* ≈ 50−70 K. As a result, a sharp peak with significantly different amplitudes for LuB and LuB is recorded in the temperature dependences of the Hall coefficient R( T) near T*. A significant (about 10%) difference (in absolute value) of the Hall coefficients R for the LuB and LuB compounds at helium and intermediate temperatures has been found and the patterns of behavior of the dependence R( H) for T < T* in an external magnetic field H ≤ 80 kOe for LuB and LuB are shown to differ significantly. Analysis of the Curie-Weiss contribution to the magnetic susceptibility χ( T) leads to the conclusion about the formation of magnetic moments μ ≈ (0.13−0.19)μ in each unit cell of the fcc structure of LuB compounds with various isotopic compositions. The possibility of the realization of an electronic topological 2.5-order transition near T* and the influence of correlation effects in the 5 d-band on the formation of a spin polarization near the rare-earth ions in LuB is discussed. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.1134/S0021364022340033 [ABSTRACT FROM AUTHOR]

The effect of symmetry lowering for the parameters of electron transport in rare-earth dodecaborides RB12 (R = Ho, Er, Tm, Lu) with fcc crystal structure at temperatures T ≤ 150 K has been discovered. It has been shown that the anisotropy of the magnetoresistance increases sharply at the transition to the disordered cage-glass phase below T* ~ 60 K. This effect is observed in magnetic and nonmagnetic rare-earth dodecaborides, including solid solutions RxLu1–xB12 with high substitutional disorder. The role of the electron phase separation (charge stripes along the 〈110〉 direction) in these metals with open trajectories on the Fermi surface is discussed. [ABSTRACT FROM AUTHOR]

Randomness and frustration are believed to be two crucial criteria for the formation of spin glass state. However, the spin freezing occurs in some well-ordered crystals below the related temperature Tf due to the instability of each spin state, which induces the variation of either magnetic moment value or exchange energy. Here we explore the new mechanism of the in-site originated disorder in antiferromagnets Gd0.73La0.27B6 and GdB6, which is caused by the random mutual shifts of Gd3+ spins from the centrally symmetrical positions in the regular cubic lattice. The universal scaling of ESR linewidth temperature dependencies to the power law ΔH(T) ~ ((T − TD)/TD)α with α = − 1.1 ± 0.05 in the paramagnetic phase of both compounds demonstrates the identity of the origin of magnetic randomness. In Gd0.73La0.27B6 the resulting random spin configurations freeze at Tf ≈ 10.5 K where the maximum of magnetization is observed. Below Tf the splitting of ZFC and FC magnetization curves takes place as well as the magnetic state depends on the antecedent sample history. In the case of GdB6 the coherent displacement of Gd ions compete with these random shifts forming an antiferromagnetic (AFM) phase at TN = 15.5 K, which prevails over the spin freezing at Tf ≈ 13 K, expected from the ESR data. The observation of the hysteresis of the ESR spectrum in the AFM phase suggests that its properties may be determined by the competition of two types of AFM orders, which results in formation of stable magnetic domains with nonequivalent positions of AFM Gd pairs at T < 10 K. [ABSTRACT FROM AUTHOR]

The antiferromagnetic ground state has been studied by transverse magnetoresistance, heat capacity and magnetization measurements, which were carried out on high quality single crystals of Tm0:996Yb0:004B12 dodecaboride in strong magnetic fields at liquid helium temperatures. Both antiferromagnetic-paramagnetic (AFP) and spin-orientation (AF1-AF2) phase transitions have been observed, and allowed to construct a complicated magnetic H-T phase diagram for this compound. Strong magnetoresistance anisotropy was found both in AF states (ρ(H∥[110])/ρ(H∥[111]) ~ 1:2 at H ~ 20 kOe) and at the critical field of AF-P transition (HN[100]/HN[111] ~ 1:25) in this magnetic metal with a simple fcc crystal structure. [ABSTRACT FROM AUTHOR]

The antiferromagnetic ground state has been studied by transverse magnetoresistance, heat capacity and magnetization measurements, which were carried out on high quality single crystals of Tm0.996Yb0.004B12 do-decaboride in strong magnetic fields at liquid helium temperatures. Both antiferromagnetic-paramagnetic (AF-P) and spin-orientation (AF1-AF2) phase transitions have been observed, and allowed to construct a complicated magnetic H-T phase diagram for this compound. Strong magnetoresistance anisotropy was found both in AF states (p(H∣∣[110])/p(H∣∣[111]) ~ 1:2 at H ~ 20 kOe) and at the critical field of AF-P transition (HN[100]/HN[111] ~ 1:25) in this magnetic metal with a simple fcc crystal structure. [ABSTRACT FROM AUTHOR]

We report the study of spin relaxation in the Eu1− xGd xB6 (0 ≤ x ≤ 0.039) single crystals with the help of 60 GHz electron spin resonance (ESR) technique. A drastic change in the linear slopes of the temperature dependences of the ESR linewidth is discovered in the paramagnetic phase of Eu1− xGd xB6. The corresponding crossover temperature T0 is shown to decrease from T0( x = 0) ∼ 60 K down to T0( x = 0.039) ∼ 15 K under rising of Gd content. A non-bottlenecked Korringa relaxation is discussed as the main factor that governs spin dynamics in the unordered state of Eu1− xGd xB6 below T0. Using of the band parameters extracted from static magnetic and transport data allows to estimate on-site exchange constant between localized spins and itinerant electrons, which is effectively tuned from 110 meV for x = 0 down to 43 meV for x = 0.039 under gradual filling of the Eu1− xGd xB6 conduction band. [ABSTRACT FROM AUTHOR]

In the system Tm1-xYbxB12 the specific heat has been studied in a wide range of Yb-concentration in the vicinity of the quantum critical point xC ≈ 0.3. The results were obtained on high quality single crystalline samples of Tm0.7Yb0.3B12 compound placed near quantum critical point, both for antiferromagnetic metals (x < xC) as well as for paramagnetic insulators (x > xC) within a wide temperature range of 1.9-300 K in magnetic field up to 9 T. The temperature dependence of the magnetic contribution to specific heat for Tm0.74Yb0.26B12 shows a logarithmic divergence of the form: Cmag/T∿-lnT at T<4 K, which may be attributed to the quantum critical regime, and it is suppressed by strong external magnetic field. The Schottky anomaly of the magnetic contribution to specific heat in Tm1-xYbxB12 has been established and analyzed in detail. [ABSTRACT FROM AUTHOR]

The magnetoresistance (MR) Δρ/ρ of the cage-glass compound HoxLu1-xB12 with various concentrations of magnetic holmium ions (x≤0.5) has been studied in detail concurrently with magnetization M(T) and Hall effect investigations on high-quality single crystals at temperatures 1.9-120 K and in magnetic field up to 80 kOe. The undertaken analysis of Δρ/ρ allows us to conclude that the large negative magnetoresistance (nMR) observed in the vicinity of the Néel temperature is caused by scattering of charge carriers on magnetic clusters of Ho3+ ions, and that these nanosize regions with antiferromagnetic (AF) exchange inside may be considered as short-range-order AF domains. It was shown that the Yosida relation -Δρ/ρ ~ M2 provides an adequate description of the nMR effect for the case of Langevin-type behavior of magnetization. Moreover, a reduction of Ho-ion effective magnetic moments in the range 3-9 μB was found to develop both with temperature lowering and under the increase of holmium content. A phenomenological description of the large positive quadratic contribution Δρ/ρ ~ μ2DH2 which dominates in HoxLu1-xB12 in the intermediate temperature range 20-120 K allows us to estimate the drift mobility exponential changes μD ~ T-α with α = 1.3-1.6 depending on Ho concentration. An even more comprehensive behavior of magnetoresistance has been found in the AF state of HoxLu1-xB12 where an additional linear positive component was observed and attributed to charge-carrier scattering on the spin density wave (SDW). High-precision measurements of Δρ/ρ=f(H,T) have allowed us also to reconstruct the magnetic H-T phase diagram of Ho0.5Lu0.5B12 and to resolve its magnetic structure as a superposition of 4f (based on localized moments) and 5d (based on SDW) components. [ABSTRACT FROM AUTHOR]

Based on low-temperature resistivity, heat capacity, and magnetization investigations, we show that the unusually strong suppression of superconductivity in LuxZr1−xB12 (x<8%) BCS-type superconductors is caused by the emergence of static spin polarization in the vicinity of nonmagnetic lutetium impurities. The analysis of the obtained results points to a formation of static magnetic moments with μeff≈6μB per Lu3+ ion (¹S0 ground state, 4f14 configuration) incorporated in the superconducting ZrB12 matrix. The size of these spin-polarized nanodomains was estimated to be about 5 Å. [ABSTRACT FROM AUTHOR]

The spatial spin modulated structure (SSMS) of the cycloid type present in bulk BiFeO 3 prevents the linear magnetoelectric effect. One way to influence this structure is to reduce the crystal size to the nanoscale. Various opinions are circulating in the literature about the effect of nanocrystal size on SSMS, and to investigate this issue, we used a number of methods, with zero-field NMR (ZF NMR) spectroscopy at the forefront. ZF NMR spectroscopy enables the direct observation of the distribution profile of local fields on iron atoms and defines the SSMS presence and its properties. We also examined the synthesized samples using XRD, TEM, and magnetometry. We conclude that SSMS persists as the nanocrystal size decreases to the cycloid period and less, becoming more harmonic. This is accompanied by the change of the anisotropy type from an "easy axis" to an "easy plane". Magnetic measurements show a significant increase in the saturation magnetization, remanent magnetization, coercivity, and exchange bias of nanocrystals with sizes close to the cycloid period, which is probably associated with incomplete spin compensation in the case of an incomplete cycloid period. Despite the fact that SSMS is retained in the samples with decreased size, the magnetic properties experience a sharp increase up to applicable values.

Randomness and frustration are believed to be two crucial criteria for the formation of spin glass state. However, the spin freezing occurs in some well-ordered crystals below the related temperature T f due to the instability of each spin state, which induces the variation of either magnetic moment value or exchange energy. Here we explore the new mechanism of the in-site originated disorder in antiferromagnets Gd 0.73 La 0.27 B 6 and GdB 6 , which is caused by the random mutual shifts of Gd 3+ spins from the centrally symmetrical positions in the regular cubic lattice. The universal scaling of ESR linewidth temperature dependencies to the power law ΔH(T) ~ ((T - T D )/T D ) α with α = - 1.1 ± 0.05 in the paramagnetic phase of both compounds demonstrates the identity of the origin of magnetic randomness. In Gd 0.73 La 0.27 B 6 the resulting random spin configurations freeze at T f  ≈ 10.5 K where the maximum of magnetization is observed. Below T f the splitting of ZFC and FC magnetization curves takes place as well as the magnetic state depends on the antecedent sample history. In the case of GdB 6 the coherent displacement of Gd ions compete with these random shifts forming an antiferromagnetic (AFM) phase at T N  = 15.5 K, which prevails over the spin freezing at T f  ≈ 13 K, expected from the ESR data. The observation of the hysteresis of the ESR spectrum in the AFM phase suggests that its properties may be determined by the competition of two types of AFM orders, which results in formation of stable magnetic domains with nonequivalent positions of AFM Gd pairs at T < 10 K.

Seebeck effect in the crystalline samples of Eu x Yb 1-x B 6 ( x = 0, 0.082, 0.127, 0.9, 1) was investigated at temperatures 2-300 K. For all the compounds thermopower is shown to be well described by the sum of diffusion ( S d = AT ) and phonon drag components. The latter contribution is induced by quasilocal (Einstein) modes of ytterbium and europium ions with characteristic temperatures Θ E (YbB 6 ) ≈ 91 K and Θ E (EuB 6 ) ≈ 122 K. The estimation of effective mass m * of the charge carriers proves that increasing of Eu content induces crossover from 'heavy' holes with m h * ( x ⩽ 0.127) ≈ 0.3-0.36 m 0 to 'light' electrons with m e * ( x ⩾ 0.9) ≈ 0.12-0.13 m 0 ( m 0 -free electron mass). For the Eu-rich compounds we propose the existence of additional point on the phase diagram, which corresponds to short-range magnetic order with enhanced spin fluctuations preceding the stabilization of magnetic polarons., (© 2020 IOP Publishing Ltd.)

Accurate low temperature charge transport measurements in combination with high-precision x-ray diffraction experiments have allowed detection of the symmetry lowering in the single domain Tm 0.19 Yb 0.81 B 12 crystals that belong to the family of dodecaborides with metal-insulator transition. Based on the fine structure analysis we discover the formation of dynamic charge stripes within the semiconducting matrix of Tm 0.19 Yb 0.81 B 12 . The charge dynamics in these conducting nano-size channels is characterized by broad-band optical spectroscopy that allowed estimating the frequency (~2.4 × 10 11 Hz) of quantum motion of the charge carriers. It is suggested that cooperative Jahn-Teller effect in the boron sublattice is a cause of the large-amplitude rattling modes of the Tm and Yb ions responsible for the 'modulation' of the conduction band along one of the [Formula: see text] directions through the variation of 5d-2p hybridization of electron states.

Electron spin resonance (ESR) in strongly correlated metals is an exciting phenomenon, as strong spin fluctuations in this class of materials broaden extremely the absorption line below the detection limit. In this respect, ESR observation in CeB 6 provides a unique chance to inspect Ce 3+ magnetic state in the antiferroquadrupole (AFQ) phase. We apply the original high frequency (60 GHz) experimental technique to extract the temperature and angular dependences of g-factor, line width and oscillating magnetization. Experimental data show unambiguously that the modern ESR theory in the AFQ phase considering the Γ 8 ground state of Ce 3+ ion completely fails to predict both the g-factor magnitude and its angular dependence. Alignment of the external magnetic field along [100] axis induces a strong (more than twofold) broadening of ESR line width with respect to the other crystallographic directions and results also in the anomalous temperature dependences of the g-factor and oscillating magnetization. In this experimental geometry the latter parameter surprisingly exceeds total static magnetization by 20% at T* ~ 2.5 K. We argue that the unusual physical picture of ESR in CeB 6 may be strongly affected by spin fluctuations and dynamic collective effects predominantly pronounced in [100] direction.