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A study of the charge transport, magnetization, and high frequency (ω/2π=60 GHz) electron spin resonance (ESR) has been carried out on La1-xCaxMnO3 single crystals corresponding to the dielectric side of the concentration driven metal-insulator transition (x≤xMIT∼0.22). For x=0.22 the onset of ferromagnetism below the Curie temperature TC≈183 K was found to induce crossover from holelike (T>TC) to electronlike (TTC. A large enhancement of the Hall effect, which is accompanied by the increase in Hall mobility to the values of μH∼-20 cm2/V s, was observed at intermediate temperatures 150 KTC was shown to evolve into an intricate two-mode ESR spectrum with irregular fine structure characterizing the ferromagnetic insulating (FI) state formed below TC. The anomalies of charge transport and magnetic properties found in FI state seem to be associated with the peculiarities of strongly disordered state with phase separation (ferromagnetic metallic domains embedded in the insulating matrix of La1-xCaxMnO3). [ABSTRACT FROM AUTHOR]

The high-field region of the magnetic phase diagram of MnSi is probed by magnetization, resistivity, and magnetoresistance measurements carried out in the temperature range 1.8-300 K for magnetic fields up to 8 T. It is shown that the phase boundary between the paramagnetic (PM) phase and the spin-polarized (SP) phase has no positive slope as was suggested previously, and appears to be practically vertical at the transition temperature Tc ∼ 30 K We argue that the broad maxima of the resistivity and magnetization derivative, which develop in the range T > Te, are determined by the specific form of functional dependences of these quantities in the PM phase and do not correspond to any "diffuse" SP-PM transition. A universal relation between magnetoresistance and magnetization δp/p = --a0M2 found in the PM phase of MnSi is shown to hold in a wide temperature and magnetic field range where magnetoresistance varies by more than two orders of magnitude. The analysis of the transport and magnetic resonance data favors the explanation of the magnetic properties of MnSi by Heisenberg-type localized magnetic moments rather than within the magnetism of itinerant electrons. A low-temperature anomaly at T ∼ 15 K corresponding to the features of magnetoresistance and g factor is reported. [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]

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 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]

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]

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 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]

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]