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Kooperativní jevy v cerových sloučeninách na hranici magnetismu
Moudřík, Jan ; Prokleška, Jan (advisor) ; Javorský, Pavel (referee)
This work reports on physical properties of a novel CeCo0.715Si2.285 compound. The compound crystallizes in the I-4m2 space group structure with extremely elongated unit cell (a = 4.13˚A , c = 32.84˚A) containing BaAl4 structural patterns. In zero magnetic field it orders antiferromagnetically at TN = 10.0K. Under application of magnetic field along the c-axis it manifests numerous magnetic transitions in small fields (B < 0.5T), resembling the so-called 'devil's staircase' behaviour (e.g. CeSb, CeCoGe3). The magnetization is almost constant from 1T up to 45T for H||c but considerably reduced (0.3µB/Ce) with respect to the free Ce3+ ion. For fields applied along the a-axis typical behaviour for a hard axis in a material with uniaxial anisotropy is observed. The performed single crystal neutron diffraction experiment did not allow complete determination of magnetic structure. 1
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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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Preparation of pure metals - analysis of the materials purity using physical quantities.
Proschek, Petr ; Pospíšil, Jiří (advisor) ; Prokleška, Jan (referee)
The thesis deals with the purity of lanthanoids and their purification using the solid state electrotransport (SSE). This method is used for high-level purification of metals. This process is really slow and is suitable especially for need of science. For this method we have prepared the cer and praseodym samples in monoarc and applicated SSE process on them. Afterthat we measured RRR (residual resistivity ratio) using four-point connection of the samples of cer and praseodym before and after the purification process and compared the values. The metals after SSE method always show a higher RRR value which means the lower level of impurities. Powered by TCPDF (www.tcpdf.org)
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Studium magnetismu ve sloučeninách CeTX3
Moudřík, Jan ; Prokleška, Jan (advisor) ; Javorský, Pavel (referee)
Solid solutions of BaNiSn3 type CeTX3 (T and X denote a transition met- al and Si/Ge, respectively) compounds were studied. Polycrystalline samples of solid solutions CeCoxRh1−xSi3 (x = 0.5, x = 0.8, x = 0.9 and x = 1.0) and CeIr(SixGe1−x)3 (x = 0.1, x = 0.4, x = 0.6 and x = 0.8) were successfully grown. A superconducting transition at 0.7-0.9 K was exhibited by all four compositions of the solution CeCoxRh1−xSi3. Based on measurements of specific heat, we con- clude that the superconductivity is probably caused by impurity phases. We have determined crystallographic, thermodynamic and magnetic properties of the solu- tion CeIr(SixGe1−x)3. Magnetic phase transition temperatures were established, the character of the transitions changed significantly in all four compositions, the temperatures themselves did not. 1
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Influence of the external pressure on the magnetic behavior of the material
Valenta, Jaroslav ; Prchal, Jiří (advisor) ; Prokleška, Jan (referee)
This thesis deals with magnetic properties of the HoCo2 compound, which is composed of rare earth and transition metal elements. The study is focused on properties at ambient pressure and changes of the magnetic behavior of the material under hydrostatic pressure. At the ambient pressure, there was performed analysis of the sample quality with a finding of presence of three magnetic transitions: flipping temperature magnetization of Co clusters Tf = (125 ± 1) K, Curie temperature TC = (79,5 ± 0,1) K and spin-reorientation temperature TR = (16,4 ± 0,5) K. When applying the hydrostatic pressure up to 3 GPa, there was observed a shift of the temperatures of the magnetic transitions and in the case Tf and TR their consequent vanishing. From the shifts of the TC and Tf towards lower temperatures and from the vanishing of the Tf, it was concluded that Co magnetism is being suppressed by the influence of the hydrostatic pressure.
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Magnetokrystalová anizotropie ve sloučeninách TbTX
Klicpera, Milan ; Javorský, Pavel (advisor) ; Prokleška, Jan (referee)
Title: The magnetocrystalline anizotropy in the TbTX compounds Author: Milan Klicpera Department: Department of Condensed Matter Physics Supervisor: doc. Mgr. Pavel Javorský, Dr. Supervisor's e-mail address: javor@mag.mff.cuni.cz Abstract: The subject of this work is the study of structural, magnetic and trans- port properties of the TbNi(Al,In) series to finding connections between magne- tocrystalline anisotropy and lattice parameters of the structure of the TbTX com- pounds. Polycrystalline TbNiAl1−xInx samples were prepared by melting. The phase and crystal structure analysis were provided on samples. We performed the measurements of the magnetization, susceptibility, specific heat, resistivity, low temperature X-ray diffraction and powder neutron diffraction. From the neutron diffraction data we refined lattice parameters and propagation vectors of the series. The main propagation is (000) and second weaker component has the propagation vector (1 2 0 1 2 ). The change of the magnetocrystalline anisotropy from uniaxial to planar type occurs for compounds with x between 0.4 and 0.5. Keywords: magnetization, X-ray and neutron diffraction, electrical resistivity.
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Magnetokalorické materiály pro ekologicky šetrné chlazení
Burianová, Simona ; Kalbáčová Vejpravová, Jana (advisor) ; Prokleška, Jan (referee)
Nazev prace: Magnetokaloricke material> pro ekologicky setrne chlazeni Aulor: Simona Burianova Kaledra ( ustav ): Katcdra fy/iky kondenzovanych latek Vcdouci bakalafske prace: RNDr. Jaua PoltierovaVcjpravova, Pb.D E-mail vedoucibo: Abslrakt: V teto bakalafske praci jc porovnavan magnctokaloricky jev dvou ruznych materialu - nanocastic ferritu hofecnateho a slouceninach TbGei_xSix obohaccnych germaniein. Magncticke vlastnosti magnctickych nanocastic mu/ou byt konlrolovany ponioei jejich tvaru a velikosli, coz rmize byt vyhodne pro jejich pouziti pfi magnetickem chlazeni. Zmcna entropie MgFciO.! byla ziskana z mefeni magnetickych kfivek pfi ruznych teplotach. Slouceniny TbSio.iOeo,, a TbsSij byly pfipraveny metodou obloukovcho taveni a jejich krystalicka struklura byla potvrzena pomoci rentgenove dii'rakce. llodnoty MCE byly ziskany z mefeni zuvislosli tepelne kapacity na magnetickem poll a leplote. Diskulovany jsou take rozdily mezi hodnotami AS v magnetickych nanocasticich MgFe:O4 a v sloueenine TbSia.|Geo(,. Klicova slova: Magnclokaloricky jev. magneticke nanocastice, kovy vzacnyeh zemin Title: Magnetocaloric materials for environment friendly refrigeration Author: Simona Burianova Department: Department of Condensed Matter Physics Supervisor: RNDr. Jana PoltierovaVejpravova, Ph.D Supervisor's e-mail...
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Magnetoelastic phenomena in the compounds of Er (Co, X) 2, X = p-element
Prokleška, Jan
The ErCo2 compound belong to a group of RECo2 compounds (R - rare earth) crystallizing in the cubic Laves phase C15. The inuence of substitution of p-element (3% of Al, Si, Ga, Ge, In in Co) on magnetic, transport and magnetoelastic properties was studied in this work. All substitutions shifts transition temperature to higher temperatures (from 43 K in the case of Ga to 52 K in the case of In). The In substitution shows the most dierent behavior in comparison to the data of pure ErCo2 compound - transition temperature shifted from 33 K to 52 K, phase transition is of the second order contrary to pure ErCo2 and no metamagnetic transition above TC was observed.
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