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Magnetic Phase Transitions and Thermal Properties of Ho(Co_{1-x}Si_x)_2 Compounds

100%
Vasylyev D., Prokleška J., Sechovský V.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
347-350
EN
The specific heat of HoCo_2 and Ho(Co_{0.95}Si_{0.05})_2 was measured as a function of temperature in several constant magnetic fields up to 8 T. A data analysis allowed us to determine the isothermal entropy change and the magnetocaloric effect in a wide temperature range. The considerable values of the magnetocaloric effect in the vicinity of the magnetic ordering transition are qualifying both compounds as suitable for magnetic refrigeration purposes. The magnetic phase transition temperature (T_C) increases from 77 K for HoCo_2 to 103 K for Ho(Co_{0.95}Si_{0.05})_2 while the large magnetocaloric effect in the vicinity of TC is maintained, which demonstrates possible ways of tuning the operating temperatures of the magnetic refrigerant.
2
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Electronic Structure of PrCo_2Ge_2

88%
Diviš M., Vejpravová J., Rusz J., Prokleška J., Sechovský V.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
295-298
EN
The intermetallic compound PrCo_2Ge_2 exhibits very interesting physical properties: antiferromagnetism below T_N = 28 K, an order to order transition at T_R = 8 K, a rich magnetic phase diagram, and huge magnetocrystalline anisotropy as observed by recent experiments on a single crystal in a magnetic field up to 14 T. We performed first principles calculations based on the density functional theory. The localized 4f^2 configuration of Pr^{3+} was treated using the open core approximation. The electronic densities of states were obtained and the position of the Fermi level was found. The hybridization between the Co-3d, Pr-5d and Ge-4p states is discussed. The calculated magnetic moment of Co is found to be quite small (m_{Co} < 0.1 μ_B). The first principles calculations of the crystal field interaction were performed as well: the obtained crystal field parameters were used as the starting parameters for further refinement in comparison with experimental data of the magnetic susceptibility and specific heat. The crystal field splitting of the 4f states was determined.
3
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Magnetic Properties of a Novel CeCo_{0.715}Si_{2.285} Compound

88%
Moudřík J., Prokleška J., Pospíšil J., Sechovský V., Císařová I.
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EN
We report on the basic physical properties of a novel CeCo_{0.715}Si_{2.285} compound, mainly its rich magnetic phase diagram. The compound crystallizes in the I-4m2 space group structure with extremely elongated unit cell (a = 4.12 Å, c = 32.84 Å). In a zero magnetic field it orders antiferromagnetically at T_{N} = 10.5 K with another order-to-order transition at 9.5 K. Under application of a magnetic field along the c-axis it manifests numerous magnetic transitions in small fields (B < 500 mT), resembling the so-called "devil's staircase" systems. Above 1 T the magnetization is almost constant up to 14 T (maximum magnetic field applied within our study) but considerably reduced (0.3 μ_B/Ce) with respect to the free Ce^{3+} ion. After removing the applied field, however, the high field state remains unchanged to be removed in negative fields. The compound also exhibits strong hysteresis of magnetization with respect to varying temperature or magnetic field. For fields applied along the a-axis typical behavior for the hard axis in the material with uniaxial anisotropy is observed.
4
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Magnetic Order in TbPdIn

88%
Javorský P., Fikáček J., Prokleška J., Nishigori S., McIntyre G.
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issue 5
879-880
EN
The magnetic structure in TbPdIn was investigated by neutron diffraction experiments. The results reveal a long-range magnetic structure with propagation vector (0,0,0) and the Tb moments forming a non-collinear structure within the basal plane that is unchanged over the whole temperature region below the ordering temperature of 66 K.
5
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Magnetism in RCo_{2} (R = Dy, Ho, Er, Tm) Under Hydrostatic Pressure

64%
Prchal J., Šebesta J., Valenta J., Míšek M., Turčinková D., Lapčák L., Prokleška J., Kratochvílová M., Sechovský V.
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vol. 126
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issue 1
288-289
EN
The short-range parimagnetic configurations, observed in the heavy rare-earth RCo_{2} compounds in paramagnetic range far above the Curie temperature T_{C}, consist in formation of ferromagnetic cobalt clusters antiferromagnetically coupled to the neighboring R magnetic moments. The characteristic temperature of the onset of parimagnetism T_{f} is very sensitive to changes of external conditions like pressure or composition. The pressure coefficients ∂T_{f}/∂p and ∂T_{C}/∂p are comparable, indicating a close connection of underlying mechanisms. Our recent measurements indicate systematic evolution of the pressure coefficients with spanning the rare-earth series from Dy through Tm in RCo_{2} with a specific case TmCo_{2}.
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