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New magnetic state of intermetallics - parimagnetism - in RCo2-type compound
Šebesta, Jakub ; Prchal, Jiří (advisor) ; Prokleška, Jan (referee)
A sample of TmCo2 compound was prepared and studied by means of temperature dependence of an electric resistivity, specific heat, magnetisation and AC magnetic susceptibility, all in ambient pressure. We have observed anomalies in the temperature dependence of specific heat at the temperatures TC Tm = (3,60 ± 0,05) K and TC Co = (4,6 ± 0,1) K, which are in the agreement with anomalies in the data of other physical variables. By comparison with HoCo2 and ErCo2 compounds, there was made a suggestion, that the characteristic temperatures correspond to the magnetic order of the Tm and Co sub-lattices. After that, temperature dependencies of AC magnetic susceptibility under external hydrostatic pressures up to 3 GPa were measured. We observed anomalies mentioned above in the measured data and moreover one more anomaly around 35 K. This anomaly corresponds most probably to the flipping temperature Tf of the magnetisation of Co clusters through the plain perpendicular to the magnetic moment of the nearest rare-earth atom. From the set of the realized pressure points we estimated pressure coefficients for the characteristic temperatures ∂TC Tm /∂p = (0,40±0,02) K·GPa-1 and ∂Tf/∂p ~ 0 K·GPa-1, . Roughly zero values of coefficients are significant, because of comparison with other RCo2-type compound.
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Pressure-induced changes of magnetic behavior of RCo2-type compounds
Valenta, Jaroslav ; Prchal, Jiří (advisor) ; Kamarád, Jiří (referee)
The diploma thesis is focused on the study of pressure-induced changes in a behavior of RECo2-type compounds. HoCo2 and its substitution of Si instead of Co in Ho(Co1-xSix)2, x = 0,025 were chosen as a representative compounds from this family of materials. Measurements of electric resistivity, heat capacity, magnetization and AC magnetic susceptibility under ambient pressure showed presence of three magnetic transitions for both samples: the change of the easy magnetization direction at TR ~ 16 K, the Curie temperature TC ~ 80 K and the flipping of magnetization of Co magnetic moments into the parallel direction with Ho magnetic moments at Tf ~ 125 K for HoCo2. Under hydrostatic pressures up to 3 GPa, the TR shifts to higher temperatures whereas TC and Tf, both decrease. This probably occurs due to the weakening of the Co magnetism and the strength of exchange interaction between Ho-Co sublattices. The experiment of muon spin rotation demonstrates a pressure influence to the decay of Co magnetic clusters, which occurs at lower temperatures with increasing pressure. It is evident that the hydrostatic pressure directly influences the exchange interaction between Co-Co.
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Pressure-induced changes of magnetic behavior of RCo2-type compounds
Valenta, Jaroslav
The diploma thesis is focused on the study of pressure-induced changes in a behavior of RECo2-type compounds. HoCo2 and its substitution of Si instead of Co in Ho(Co1-xSix)2, x = 0,025 were chosen as a representative compounds from this family of materials. Measurements of electric resistivity, heat capacity, magnetization and AC magnetic susceptibility under ambient pressure showed presence of three magnetic transitions for both samples: the change of the easy magnetization direction at TR ~ 16 K, the Curie temperature TC ~ 80 K and the flipping of magnetization of Co magnetic moments into the parallel direction with Ho magnetic moments at Tf ~ 125 K for HoCo2. Under hydrostatic pressures up to 3 GPa, the TR shifts to higher temperatures whereas TC and Tf, both decrease. This probably occurs due to the weakening of the Co magnetism and the strength of exchange interaction between Ho-Co sublattices. The experiment of muon spin rotation demonstrates a pressure influence to the decay of Co magnetic clusters, which occurs at lower temperatures with increasing pressure. It is evident that the hydrostatic pressure directly influences the exchange interaction between Co-Co.
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Magnetism in the RCo2-type compounds
Šebesta, Jakub ; Prchal, Jiří (advisor) ; Prokleška, Jan (referee)
Magnetic properties of RCo2 compounds have been studied since the sec- ond half of the last century. However, there was recently observed new mag- netic state, so-called parimagnetism. The aim of this thesis was to find the real behavior of TmCo2, which exhibits many discrepancies in the published results, by means of preparation of high-quality single-crystals, its characteri- zation around the ordering temperature and to study parimagnetic behavior. Obtained results showed differences between the samples, which should be caused by the instability of Co and Tm magnetism. It might be the reason of discrepancies in the literature. The results however show the same struc- ture of measured curves with two present phase transition. We suggest two possible interpretations: a) magnetic reorientation of Tm magnetic moments below the ordering temperature of the Tm sub-lattice or b) consequent or- dering of the rare-earth sub-lattice followed by ordering of the Co sub-lattice at lower temperature, which seems to be more realistic. We observed pari- magnetic anomalies at 38 K, 80 K, 168 K only in the case of single-crystals containing small amount of impurity phase, which probably affects the for- mation of magnetic clusters. 1
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Pressure-induced changes of magnetic behavior of RCo2-type compounds
Valenta, Jaroslav
The diploma thesis is focused on the study of pressure-induced changes in a behavior of RECo2-type compounds. HoCo2 and its substitution of Si instead of Co in Ho(Co1-xSix)2, x = 0,025 were chosen as a representative compounds from this family of materials. Measurements of electric resistivity, heat capacity, magnetization and AC magnetic susceptibility under ambient pressure showed presence of three magnetic transitions for both samples: the change of the easy magnetization direction at TR ~ 16 K, the Curie temperature TC ~ 80 K and the flipping of magnetization of Co magnetic moments into the parallel direction with Ho magnetic moments at Tf ~ 125 K for HoCo2. Under hydrostatic pressures up to 3 GPa, the TR shifts to higher temperatures whereas TC and Tf, both decrease. This probably occurs due to the weakening of the Co magnetism and the strength of exchange interaction between Ho-Co sublattices. The experiment of muon spin rotation demonstrates a pressure influence to the decay of Co magnetic clusters, which occurs at lower temperatures with increasing pressure. It is evident that the hydrostatic pressure directly influences the exchange interaction between Co-Co.
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Pressure-induced changes of magnetic behavior of RCo2-type compounds
Valenta, Jaroslav ; Prchal, Jiří (advisor) ; Kamarád, Jiří (referee)
The diploma thesis is focused on the study of pressure-induced changes in a behavior of RECo2-type compounds. HoCo2 and its substitution of Si instead of Co in Ho(Co1-xSix)2, x = 0,025 were chosen as a representative compounds from this family of materials. Measurements of electric resistivity, heat capacity, magnetization and AC magnetic susceptibility under ambient pressure showed presence of three magnetic transitions for both samples: the change of the easy magnetization direction at TR ~ 16 K, the Curie temperature TC ~ 80 K and the flipping of magnetization of Co magnetic moments into the parallel direction with Ho magnetic moments at Tf ~ 125 K for HoCo2. Under hydrostatic pressures up to 3 GPa, the TR shifts to higher temperatures whereas TC and Tf, both decrease. This probably occurs due to the weakening of the Co magnetism and the strength of exchange interaction between Ho-Co sublattices. The experiment of muon spin rotation demonstrates a pressure influence to the decay of Co magnetic clusters, which occurs at lower temperatures with increasing pressure. It is evident that the hydrostatic pressure directly influences the exchange interaction between Co-Co.
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New magnetic state of intermetallics - parimagnetism - in RCo2-type compound
Šebesta, Jakub ; Prchal, Jiří (advisor) ; Prokleška, Jan (referee)
A sample of TmCo2 compound was prepared and studied by means of temperature dependence of an electric resistivity, specific heat, magnetisation and AC magnetic susceptibility, all in ambient pressure. We have observed anomalies in the temperature dependence of specific heat at the temperatures TC Tm = (3,60 ± 0,05) K and TC Co = (4,6 ± 0,1) K, which are in the agreement with anomalies in the data of other physical variables. By comparison with HoCo2 and ErCo2 compounds, there was made a suggestion, that the characteristic temperatures correspond to the magnetic order of the Tm and Co sub-lattices. After that, temperature dependencies of AC magnetic susceptibility under external hydrostatic pressures up to 3 GPa were measured. We observed anomalies mentioned above in the measured data and moreover one more anomaly around 35 K. This anomaly corresponds most probably to the flipping temperature Tf of the magnetisation of Co clusters through the plain perpendicular to the magnetic moment of the nearest rare-earth atom. From the set of the realized pressure points we estimated pressure coefficients for the characteristic temperatures ∂TC Tm /∂p = (0,40±0,02) K·GPa-1 and ∂Tf/∂p ~ 0 K·GPa-1, . Roughly zero values of coefficients are significant, because of comparison with other RCo2-type compound.
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