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Magnetocaloric properties of rare-earth compounds
Kaštil, Jiří ; Javorský, Pavel (advisor) ; Kolomiets, Alexander (referee) ; Solzi, Massimo (referee)
This work presents study of magnetocaloric properties of compounds exhibiting unusual magnetic characteristics. Several systems were studied: TbNiAl, (Tb,Y)NiAl, TbNi(Al,In), TbFeAl, GdFeAl, Ni2MnGa based compounds and amorphous metallic alloy Gd-Co-Al-Y. Influence of magneto-crystalline anisotropy on magnetocaloric effect was studied on singlecrystalline sample of TbNiAl compound. The maximum of entropy change was measured with orientation of magnetic field along c axis and compared to polycrystalline sample a 100% increase was observed. Substitutions of Y and In in TbNiAl led to a change of magnetic ordering. Both substitution led to increase of RCP values of studied material. TbFeAl and GdFeAl compounds, characterized by partial disorder of Fe and Al atoms, showed magnetocaloric effect in wide temperature region which led to interesting values of RCP~350 J kg-1 . Very broad region of magnetocaloric effect was also observed on amorphous metallic material of Gd-Co-Al-Y. The effect of Er substitution in Ni2MnGa based compound on its magneto-structural transition, connected with inverse magnetocaloric effect, was studied. The direct measurement method of adiabatic temperature change is described and instrument for such measurement, developed in collaboration with FZU AVČR, v.v.i., is presented.
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Vliv substitucí na magnetokalorický jev u vybraných sloučenin vzácných zemin
Kaštil, Jiří
The anisotropy of the magnetocaloric effect was studied on DyNiAl single crystal. Our data reveal a strong anisotropy of the magnetocaloric effect. The large effect occurs for field applied along the c-axis whereas the entropy change is small for the perpendicular field direction. The influence of substitution on the magnetocaloric effect was measured in the Gd(Co1-xRhx)2 compounds (where x was from 0.05 to 0.30) and Dy(Co1-xFex)2 compounds (where x was from 0.00 to 0.03). The substitution of Co by Rh leads to a decrease of the transition temperature, Tc, and increase of the maximum entropy change. The Tc increases but the maximum of entropy change quickly decreases in case of Fe substitution. The last studied systems were the Gd1-xTbx alloys with x in range from 0.00 to 0.40. The influence of the sample shape and orientation was studied. The thin ribbon oriented along the magnetic filed gave the highest value of the entropy change. The three measurement techniques were used: the heat capacity measurement, the magnetization measurement and the direct measurement of the temperature change.
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Magnetocaloric properties of rare-earth compounds
Kaštil, Jiří ; Javorský, Pavel (advisor) ; Kolomiets, Alexander (referee) ; Solzi, Massimo (referee)
This work presents study of magnetocaloric properties of compounds exhibiting unusual magnetic characteristics. Several systems were studied: TbNiAl, (Tb,Y)NiAl, TbNi(Al,In), TbFeAl, GdFeAl, Ni2MnGa based compounds and amorphous metallic alloy Gd-Co-Al-Y. Influence of magneto-crystalline anisotropy on magnetocaloric effect was studied on singlecrystalline sample of TbNiAl compound. The maximum of entropy change was measured with orientation of magnetic field along c axis and compared to polycrystalline sample a 100% increase was observed. Substitutions of Y and In in TbNiAl led to a change of magnetic ordering. Both substitution led to increase of RCP values of studied material. TbFeAl and GdFeAl compounds, characterized by partial disorder of Fe and Al atoms, showed magnetocaloric effect in wide temperature region which led to interesting values of RCP~350 J kg-1 . Very broad region of magnetocaloric effect was also observed on amorphous metallic material of Gd-Co-Al-Y. The effect of Er substitution in Ni2MnGa based compound on its magneto-structural transition, connected with inverse magnetocaloric effect, was studied. The direct measurement method of adiabatic temperature change is described and instrument for such measurement, developed in collaboration with FZU AVČR, v.v.i., is presented.
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|
|
Vliv substitucí na magnetokalorický jev u vybraných sloučenin vzácných zemin
Kaštil, Jiří
The anisotropy of the magnetocaloric effect was studied on DyNiAl single crystal. Our data reveal a strong anisotropy of the magnetocaloric effect. The large effect occurs for field applied along the c-axis whereas the entropy change is small for the perpendicular field direction. The influence of substitution on the magnetocaloric effect was measured in the Gd(Co1-xRhx)2 compounds (where x was from 0.05 to 0.30) and Dy(Co1-xFex)2 compounds (where x was from 0.00 to 0.03). The substitution of Co by Rh leads to a decrease of the transition temperature, Tc, and increase of the maximum entropy change. The Tc increases but the maximum of entropy change quickly decreases in case of Fe substitution. The last studied systems were the Gd1-xTbx alloys with x in range from 0.00 to 0.40. The influence of the sample shape and orientation was studied. The thin ribbon oriented along the magnetic filed gave the highest value of the entropy change. The three measurement techniques were used: the heat capacity measurement, the magnetization measurement and the direct measurement of the temperature change.
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