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Deppe, M., N. Caroca-Canales, J. G. Sereni, and C. Geibel. "Evidence for a metamagnetic transition in the heavy Fermion system CeTiGe." In Journal of Physics: Conference Series, 012026. Vol. 200. International Conference on Magnetism, ICM 2009 200, no. SECTION 1. Karlsruhe, 2010.
Abstract: A recent study of CeTiGe identified this compound as a paramagnetic heavy Fermion system where the full J = 5/2 multiplet is involved in the formation of the ground state. Here we present a preliminary investigation of the dc-magnetization Mdc(H) and of the magnetoresistance Ï(H) of polycrystalline CeTiGe samples in applied magnetic fields up to μ0H = 14 T. The results reveal a pronounced metamagnetic transition at a critical field μ0Hc ≈ 13.5 T at low temperatures, with a step like increase in Mdc(H) of at least 0.6 μB/Ce. The metamagnetic transition leads to a strong decrease in Ï(H). A clear hysteresis in Mdc(H) and Ï(H) indicate that in CeTiGe these metamagnetic features correspond to a true thermodynamic, first order type transition in contrast to the critical behavior observed in the canonical system CeRu2Si2. Measurements at higher temperatures showed a continuous suppression of the metamagnetic transition with increasing T, which vanishes at T ∼ 30 K. © 2010 IOP Publishing Ltd.
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Franco, D. G., R. E. Carbonio, and G. Nieva. "Change in the Magnetic Domain Alignment Process at the Onset of a Frustrated Magnetic State in Ferrimagnetic La2Ni(Ni1/3Sb2/3)O6 Double Perovskite." IEEE Transactions on Magnetics 49, no. 8 (2013): 4656–4659.
Abstract: We have performed a combined study of magnetization hysteresis loops and time dependence of the magnetization in a broad temperature range for the ferrimagnetic La2Ni(Ni1/3Sb2/3)O6 double perovskite. This material has a ferrimagnetic order transition at ~100 K and at lower temperatures (~20 K) shows the signature of a frustrated state due to the presence of two competing magnetic exchange interactions. The temperature dependence of the coercive field shows an important upturn below the point where the frustrated state sets in. The use of hysteresis data, magnetization versus applied magnetic field, together with the magnetization versus time data provides a unique opportunity to distinguish between different scenarios for the low temperature regime. From our analysis, a strong domain wall pinning results in the best scenario for the low temperature regime. For temperatures larger than 20 K, the adequate scenario seems to correspond to a weak domain wall pinning.
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Franco, D. G., R. E. Carbonio, and G. Nieva. "Magnetic Properties of the Double Perovskites LaPbMSbO6 (M = Mn, Co, and Ni)." IEEE Transactions on Magnetics 49, no. 8 (2013): 4594–4597.
Abstract: New double perovskites LaPbMSbO6, where M2+ = Mn2+, Co2+, and Ni2+, were synthesized as polycrystals by an aqueous synthetic route at temperatures below 1000 °C. All samples are monoclinic, space group P21/n, as it is observed from Rietveld analysis of X-ray powder diffraction patterns. The distribution of M2+ and Sb5+ among the two octahedral sites have 3% of disorder for M2+ = Ni2+, whereas for M2+ = Mn2+ and Co2+ less disorder is found. The three samples have an antiferromagnetic transition, due to the antiferromagnetic coupling between M2 + through super-superexchange paths M2+-O2--Sb5+-O2--M2+. Transition temperatures are low: 8, 10 and 17 K for Mn2+, Co2+, and Ni2 + respectively, as a consequence of the relatively long distances between the magnetic ions M2+. Besides, for LaPbMnSbO6 a small transition at 45 K was found, with ferrimagnetic characteristics, possibly as a consequence of a small disorder between Mn2+ and Sb5+. This disorder would give additional and shorter interaction paths: superexchange Mn2+-O2--Mn2+.
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Haberkorn, N., S. Suárez, S. L. Bud'ko, and P. C. Canfield. "Strong pinning and slow flux creep relaxation in Co-doped CaFe2As2 single crystals." Solid State Communications 318 (2020): 113963.
Abstract: We report on measurements of critical current densities Jc and flux creep rates S of freestanding Ca(Fe1−xCox)2As2 (x ≈ 0.033) single crystals with Tc ≈ 15.7 K by performing magnetization measurements. The magnetic field dependences of Jc at low temperature display features related to strong pinning. In addition, we find that the system displays small flux creep rates. The characteristic glassy exponent, μ, and the pinning energy, U0, display exceptional high values for pristine crystals. We find that for magnetic fields between 0.3 T and 1 T, μ decreases from ≈ 2.8 to ≈ 2 and U0 remains ≈ 300 K. Analysis of the pinning force indicates that the mechanism is similar to the observed in polycrystalline systems in which grain boundaries and random disorder produce the vortex pinning. Considering the large U0 observed in the single crystal, we attempt to improve the pinning by adding random point disorder by 3 MeV proton irradiation with a fluence of 2 × 1016 proton/cm2. The results show that, unlike other iron-based superconductors, the superconducting fraction is sharply reduced by irradiation. This fact indicates that the superconductivity in the system is extremely fragile to an increment in the disorder. The superconducting volume fraction in the irradiated crystal systematically recovers after removal disorder by thermal annealing, which evidences as to the observation of critical state in curves of magnetization versus magnetic field. No features related to a reentrant antiferromagnetic transition are observed for the irradiated sample.
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Libbrecht, S., E. Osquiguil, and Y. Bruynseraede. "Influence of field inhomogeneity on the magnetization of YBCO films." Physica C: Superconductivity and its applications 225, no. 3-4 (1994): 337–345.
Abstract: DC magnetization data of superconducting thin YBCO films, measured by means of a magnetometer in which the sample is pulled through a set of pick-up coils, are often calculated from pick-up signals which clearly deviate from the ideal response. We show how these signal distortions influence the values obtained for the magnetization, and present a simple model that enables one to simulate the temperature dependence of these distorted pick-up signals, in the case of low-field magnetization measurements. The model is based on the magnetic field inhomogeneity of the magnetometer, in combination with the hysteretic magnetization of the superconducting sample. Optimum values for the model parameters are derived and discussed.
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Luzuriaga, J., and F. de la Cruz. "Reversible magnetization of surface superconductivity." Solid State Communications 25, no. 8 (1978): 605–607.
Abstract: Direct measurements of the surface superconducting magnetization of the PbTl system shows that this state is a thermodynamic reversible one.
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Sereni, J. G., G. Schmerber, and J. P. Kappler. "Thermodynamic Behavior of Ce Compounds Close to a T->0 Critical Point." IEEE Transactions on Magnetics 49, no. 8 (2013): 4647–4651.
Abstract: There is a reduced group of Ce very heavy Fermions (VHF) which do not order magnetically down to at least T ≈ 500 mK because they are very close to a Tord = 0 critical point. These compounds are at the top of the limT→ 0 Cm/T specific heat values because they collect very high density of low energy excitations. From the analysis of Cm(T)/T and entropy Sm(T) dependencies performed on selected CePd3Mx ternaries (where M = B and Be) a quantitative evaluation of an upper limit for the density of excitations can be proposed. These observations exclude any evidence of Cm(T)/T divergency as T→ 0 in agreement with thermodynamic laws. A comparison with selected Yb-base VHF supports these features.
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