Search

High frequency (60 GHz) electron spin resonance (ESR) and magnetic susceptibility were studied for VOx multi-walled nanotubes (VOx-NTs) in the range of 4.2-300 K. It is found that apart from technological impurities, the magnetism of VOx-NTs is controlled by (i) antiferromagnetic V4+ noninteracting dimmers and (ii) V4+ quasi-free spins, which at T < 50 K form a disorder driven quantum critical state. From concentration estimates, we argue the V4+ dimers are an essential element of the VOx-NTs structure. [ABSTRACT FROM AUTHOR]

The magnetic properties of nanomaterials based on vanadium oxide (multiwall nanotubes, nanorods, and nanolayers) have been investigated in the temperature range of 1.8–220 K by high-frequency (60-GHz) EPR. A transition from a ferromagnetic temperature dependence to an antiferromagnetic temperature dependence has been observed in nanorods and nanotubes with a decrease in the temperature. The FM-AFM crossover observed near TC ∼ 110 K is accompanied by a low-temperature increase in the Curie constant by a factor of 2.7–7. The comparison of the experimental data for various VO x nanoparticles indicates that the most probable cause of the change in the type of magnetic interaction is a change in the concentration of V4+ magnetic ions. [ABSTRACT FROM AUTHOR]

The magnetoresistance Δρ/ρ of single-crystal samples of praseodymium and neodymium hexaborides (PrB6 and NdB6) has been measured at temperatures ranging from 2 to 20 K in a magnetic field of up to 80 kOe. The results obtained have revealed a crossover of the regime from a small negative magnetoresistance in the paramagnetic state to a large positive magnetoresistive effect in magnetically ordered phases of the PrB6 and NdB6 compounds. An analysis of the dependences Δρ( H)/ρ has made it possible to separate three contributions to the magnetoresistance for the compounds under investigation. In addition to the main negative contribution, which is quadratic in the magnetic field (−Δρ/ρ ∝ H2), a linear positive contribution (Δρ/ρ ∝ H) and a nonlinear ferromagnetic contribution have been found. Upon transition to a magnetically ordered state, the linear positive component in the magnetoresistance of the PrB6 and NdB6 compounds becomes dominant, whereas the quadratic contribution to the negative magnetoresistance is completely suppressed in the commensurate magnetic phase of these compounds. The presence of several components in the magnetoresistance has been explained by assuming that, in the antiferromagnetic phases of PrB6 and NdB6, ferromagnetic nanoregions (ferrons) are formed in the 5 d band in the vicinity of the rareearth ions. The origin of the quadratic contribution to the negative magnetoresistance is interpreted in terms of the Yosida model, which takes into account scattering of conduction electrons by localized magnetic moments of rare-earth ions. Within the approach used, the local magnetic susceptibility χloc has been estimated. It has been demonstrated that, in the temperature range TN < T < 20 K, the behavior of the local magnetic susceptibility χloc for the compounds under investigation can be described with good accuracy by the Curie-Weiss dependence χloc ∝ ( T − Θ p)−1. [ABSTRACT FROM AUTHOR]

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 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 concentration of carriers in LuB12 is evaluated theoretically by applying ab initio FP-LMTO calculations. Theoretical results are found to be in agreement with high-precision measurements of the Hall coefficient RH(T) carried out on single crystals of the rare-earth dodecaborides RB12 (R=Ho,Er,Tm,Lu) at temperatures 1.8–300 K. The nature of the antiferromagnetic ordering in RB12 is investigated within an RKKY-like model supplemented by comprehensive electronic structure calculations for paramagnetic, ferromagnetic, and antiferromagnetic phases. [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 concentration of carriers in LuB12 is evaluated theoretically by applying ab initio FP-LMTO calculations. Theoretical results are found to be in agreement with high-precision measurements of the Hall coefficient RH(T) carried out on single crystals of the rare-earth dodecaborides RB12 (R=Ho,Er,Tm,Lu) at temperatures 1.8–300 K. The nature of the antiferromagnetic ordering in RB12 is investigated within an RKKY-like model supplemented by comprehensive electronic structure calculations for paramagnetic, ferromagnetic, and antiferromagnetic phases. [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]