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1
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Superconductivity, Magnetism, and Atomic Rattling Phenomena in R_{3}Rh_{4}Ge_{13} (R=Y, Yb, Lu)

100%
Strydom A.
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vol. 126
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issue 1
318-321
EN
We give a first report of the physical properties of the pair of cubic intermetallic compounds R_{3}Rh_{4}Ge_{13}, with R being either Yb or Lu. The crystal structure can be described in terms of 3 atomic cages, and we reveal how certain thermal physical properties are inherent to this particular atomic layout. Close to room temperature, Yb_{3}Rh_{4}Ge_{13} displays strong paramagnetism originating from Yb^{3+} ions, but upon cooling though 100 K the magnetic susceptibility and electrical resistivity behave according to a thermally driven valence instability, and we classify Yb_{3}Rh_{4}Ge_{13} therefore as an intermediate valent f-electron system. Lu_{3}Rh_{4}Ge_{13} behaves in a diamagnetic manner throughout our accessible temperature range, - first with a weakly temperature-dependent magnetic susceptibility below room temperature, and finally with a precipitous drop in the electrical resistivity to zero at 2.5 K when superconductivity sets in.
2
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The Effect of Ce Dilution on the Ferromagnetic Ordering in CeAuGe

64%
Sondezi B., Strydom A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
228-230
EN
Transport and thermodynamic properties of the well-ordered hexagonal CeAuGe compound have been studied. This compound is known to order ferromagnetically at T_{C} = 10 K with well-defined anomalies in magnetic susceptibility χ(T), electrical resistivity ρ(T) and specific heat C_p(T) characterising the phase transition. The location of T_{C} has been observed to be unstable and enhanced even in moderate applied magnetic fields. However, the dilution of magnetic species, Ce, with the non-f electron element, La, is shown in this work to achieve a continuous suppression of T_{C} to 0 K. The integrity of the space group and the details of the unit cell occupation are retained throughout the substitution series, as is the high-temperature localized Ce-effective magnetic moment μ_{eff} = 2.54 μ_{B}/(mol Ce). Our studies of physical properties down to 0.05 K show a quantum critical form of non-Fermi liquid behaviour, characterised by a logarithmic divergence in C_p(T)/T data in the very dilute Ce content.
3
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Physical Properties Study of the CeOsGa₄ Compound

64%
Sondezi B., Strydom A.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
398-400
EN
A polycrystalline sample of CeOsGa₄ was prepared by arc-melting stoichiometric quantities of high purity elements of 4N and greater, in an arc furnace. The data was confirmed to crystallize in an orthorhombic structure, with a space group Pmma (Number 51). Measurements of the magnetic susceptibility showed a distinct anomaly around T_{o} = 3.8 K, while the high temperature data (above 100 K) obeys Curie-Weiss law. The calculated effective moment of 2.44 μ_{B}, was obtained, which was a bit less than the theoretical moment for a Ce³⁺ ion of 2.54 μ_{B}. Magnetization data at T=2 K depicts that CeOsGa₄ does not saturate up to applied magnetic field of 7 T, while the data measured at 9 K indicates that the compound is purely paramagnetic at that temperature. The low temperature specific heat data is characterized by an anomaly at T_{o} = 3.8 K confirming the χ(T) data. Electrical resistivity shows a metallic behaviour at high temperatures with a deviation at low temperatures, signalling the cooperative behaviour which results to ordering. In this work we present the initial studies of the physical properties measurements performed on this compound.
4
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Strongly Correlated Electron Behaviour in CeT_2Al_8 (T~=~Fe,~Co)

64%
Ghosh S., Strydom A.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1082-1084
EN
We report on studies of physical properties of the two compounds CeFe_2Al_8 and CeCo_2Al_8 in which we have found varying degrees of electronic correlational phenomena. No magnetic ordering was detected down to 0.4 K in either of the two compounds. At elevated temperatures an incoherent Kondo interaction between the Ce 4f-electron and the conduction electrons is prevalent in both compounds. CeCo_2Al_8 exhibits a stable 4f-electron magnetic moment, but in CeFe_2Al_8 an intermediate-valent state prevails near room temperature that eventually transforms into a Fermi-liquid ground state. The low-temperature specific heat of CeCo_2Al_8 shows typical strongly correlated electron behaviour and a - logT upturn in its electronic specific heat below about 10 K.
5
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Thermal Conductivity of Ce₂Ru₃Ga₉ Compound

64%
Falkowski M., Strydom A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
240-242
EN
The Ce-based 2:3:9 series of compounds are known for strongly correlated 4f-electron behaviour. Here, we report for the first time a study of the thermal conductivity κ(T) in zero and 9 T magnetic field for Ce₂Ru₃Ga₉ across the temperature range 2 K ≤ T ≤ 300 K. The zero-field temperature dependence of κ(T) exhibits a pronounced maximum, characteristic for metals with large electronic mean free path and towards room temperature κ(T) starts behaving in a manner usually attributed to the enhanced electron-phonon coupling. Based on the Wiedemann-Franz law the electronic and lattice contributions to the thermal conductivity were estimated. In high temperature region a distinct step-like anomaly at T* = 203 K has been observed which signals a putative phase transition, probably of phononic or lattice origin. We furthermore discuss the effect of applied magnetic fields on the thermal transport in Ce₂Ru₃Ga₉.
6
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Point Contact Properties of R_3Pd_{20}X_6 (R = La, Ce; X = Si, Ge) Cage Compounds

51%
Čurlik I., Strydom A., Reiffers M.
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issue 5
907-909
EN
Point-contact spectroscopy measurements have been performed on the R_3Pd_{20}X_6 (R = La, Ce; X = Si, Ge) cage compounds. In case of La the characteristic phonon energies have been obtained in agreement with that of the Raman scattering. In Ce_3Pd_{20}Si_6 we have observed asymmetric behaviour of dV/dI(V) dependences which was observed in non-Fermi liquid compound. In Ce_3Pd_{20}Ge_6 we have observed maxima at crystalline electric field energies, influenced by magnetic field. This is connected with quadrupolar ordering transition.
7
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Crystal Structure and Magnetic Properties of new Eu-Pd-Sn Compounds

45%
Čurlík I., Gastaldo F., Giovannini M., Strydom A., Reiffers M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1003-1005
EN
We report on the synthesis, crystal structure determination, and magnetic susceptibility measurements of Eu₃Pd₂Sn₂, EuPd₂Sn₄, and EuPdSn₂. For all three compounds a divalent state of Eu ions was obtained from the fitting of the magnetic susceptibilities. At low temperatures Eu₃Pd₂Sn₂, EuPd₂Sn₄, and EuPdSn₂ order magnetically at 23, 12, and 13 K, respectively.
8
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Magnetic and Thermodynamic Properties of Ce₄RuAl

45%
Debnath J., Strydom A., Sondezi B., Tappe F., Pöttgen R.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
237-239
EN
The results of magnetic susceptibility and heat capacity measurements are reported for the Ce₄RuAl compound above room temperature to low temperature range (400 K to 0.34 K) and in the magnetic field up to 7 T. The magnetic susceptibility χ(T) exhibits a distinct anomaly at 0.95 K which most probably suggests a paramagnetic to antiferromagnetic phase transition. The magnetic susceptibility obeys the Curie-Weiss law in the region 100-400 K and revealed an effective magnetic moment μ_{eff}=2.18 μ_{B}/Ce which is less than the value for free Ce³⁺ (μ_{eff}=2.54 μ_{B}). The paramagnetic Weiss temperature indicates net antiferromagnetic correlations. In the specific heat a peak at 1.3 K supports the bulk nature of the phase transition observed in χ(T). The Sommerfield coefficient is moderately enhanced in the paramagnetic phase, and suggests f-c correlations among the electrons prior to magnetic ordering. The obtained Sommerfield coefficient γ behavior is consistent with the Anderson model-based theoretical predictions.
9
Content available remote

Magnetocaloric Effect in Geometrically Frustrated Magnetic Compound HoB_{12}

39%
Snyman J., Flachbart K., Gabani S., Reiffers M., Shitsevalova N., Siemensmeyer K., Strydom A.
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issue 5
873-874
EN
The magnetocaloric effect of frustrated antiferromagnetic HoB_{12} is calculated. The isothermal entropy change Δ S characterising the magnetocaloric effect shows a small positive change upon magnetisation below the transition temperature T_{N}, indicating a small inverse magnetocaloric effect. At T_{N}, Δ S shows clear scaling behaviour with the applied magnetic field. The adiabatic temperature change Δ T shows paramagnetic behaviour above T_{N}, despite strong magnetic correlations that persist in this temperature region. The adiabatic temperature change calculated for HoB_{12} is appreciable.
10
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Structural and Physical Properties of the new Stannide Yb₃Pd₄Sn₁₃

33%
Gastaldo F., Giovannini M., Strydom A., Djoumessi R., Čurlík I., Reiffers M., Solokha P., Saccone A.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1006-1008
EN
Among the new discovered intermetallics in the Yb-Pd-Sn system, the cubic phase Yb₃Pd₄Sn₁₃, with a lattice parameter of 0.9743(5) nm, emerges as a new member of the R₃T₄Sn₁₃ family (R = rare earth element, T = transition metal) crystallizing in the Yb₃Rh₄Sn₁₃-structure type. The effective magnetic moment μ_{eff}=1.84 μ_{B}/Yb is strongly reduced. Moreover, measurements of magnetic properties, specific heat and resistivity indicate superconductivity below 2.4 K. This compound is found to exhibit a strongly enhanced electronic specific heat at low temperature from which we infer a possible low-lying magnetic phase transition or other source of magnetic entropy.
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