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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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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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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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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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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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Extension of instrumental capabilities in cryomagnetic laboratory
Proschek, Petr ; Prokleška, Jan (advisor) ; Javorský, Pavel (referee)
Measurement of elastic properties (thermal expansion and magnetostriction) under (multi)extreme conditions is a difficult task. In the vicinity of the room temperature or above it an abundance of methods is available, with decreasing temperature and adding magnetic field and/or hydrostatic pressure their number is limited. Dilatometric cells (either planparaller or tilted plate design) provide superior sensitivity in low temperatures and applied magnetic fields, however, cannot be used in hydrostatic cell. Common choice for the measurement of thermal expansion under hydrostatic pressure are methods based on strain-gauges, with mediocre sensitivity and more importantly a difficult or even impossible usage at very low temperatures (T ≲ 3 K). Measurement of magnetic properties (especially magnetization) under (multi)extreme conditions is also a difficult task. In the vicinity of temperature 2 K and above it an abundance of methods is available, with decreasing temperature and adding magnetic field and/or hydrostatic pressure their number is limited. VSM system provides great sensitivity, but can not be used under 2 K and hydrostatic pressure. MPMS aparature provides pressure up to 9 GPa (diamond pressure cell), but still we can not apply lower temperatures than 2 K. Our aim is to develop a simple yet sensitive...
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Kritické chování v magnetických fázových diagramech uranových sloučenin
Opletal, Petr ; Prokleška, Jan (advisor)
Title: Critical behavior in magnetic phase diagrams of uranium compounds Author: Bc. Petr Opletal Department: Department of Condensed Matter Physics Supervisor: RNDr. Jan Prokleška, Ph.D., Department of Condensed Matter Physics Abstract: This work is focused on study of phase diagrams and related critical effects in the pseudoternary UCo1-xRuxAl compound. Three single crystals of nominal composition UCo0.99Ru0.01Al, UCo0.995Ru0.005Al and UCo0.9975Ru0.0025Al have been prepared by Czochralski method in triarc furnace. Quality of single crystals was checked by EDX analysis, Laue method and XRPD. For UCo0.99Ru0.01Al Curie temperature was determined as TC = 16 K. UCo0.995Ru0.005Al shows transition from paramagnetic to ferromagnetic phase at TC= 4.5 K and at higher temperatures we observe a metamagnetic transition of first order with a critical field HC = 0.04 T. UCo0.9975Ru0.0025Al is paramagnetic to low temperatures with metamagnetic transition of first order and critical field HC = 0.55 T. Experiments in hydrostatic pressure on UCo0.995Ru0.005Al and UCo0.9975Ru0.0025Al showed decay of ferromagnetism and increase of critical field. This behavior is similar to evolution of magnetism in UCoAl and URhAl in applied hydrostatic pressure. Keywords: UCoAl, URuAl, ferromagnetism, metamagnetism
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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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Peculiarities of magnetism on the verge of ferromagnetic ordering
Opletal, Petr ; Prokleška, Jan (advisor) ; Nhu-Tarnawska, Hoa Kim Ngan (referee) ; Veis, Martin (referee)
This thesis focuses on the study of magnetic properties of three 5f electron itinerant ferromagnets UCo0.990Ru0.010Al, UCoGa and URhGa and investigation of their phase diagrams. The single crystals of high-quality were prepared by Czochralski method for all three compounds. The physical properties at ambient pressure were studied by macroscopic methods (magnetization, electrical transport and heat capacity measurements) and also by magnetic force microscopy (MFM). The measurements were done under various external conditions (high pressure, low temperatures, high magnetic field). Through all these measurements and external conditions we investigated the interesting physical properties and the ferromagnetic phase diagrams. Effect of different conditions during the preparation and the thermal treatment on UCoGa was studied on two different single crystals. We show that annealing leads to improved quality of samples and the gallium evaporation from the melt during the growth leads to lower quality in parts of the ingot closer to melt. MFM images of UCoGa below the ordering temperature show domain branching and narrow magnetic domains wall made only of neighboring atoms with opposing moments. We have grown first ever single crystal of URhGa with ferromagnetic ordering temperature TC = 41 K. Anomalous maximum in...
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