Study On New Magnetic Refrigeration Materials (Gd_1-xR_x)₅Si₄(R=Dy,Ho)

To search the new magnetic refrigeration materials which Curie temperatures are tunable in the range of near room temperatures, the authors of this paper researched on the crystal structure,the Curie temperatures, magnetic entropy change and adiabatic temperature change of (Gd_1-xD_yx)₅Si₄(x=0.1,0.2,0.3,0.35) and (Gd_1-xHo_x)₅Si₄(x=0.05,0.15,0.25) alloys that were prepared by arc melting in an argon atmosphere. X-ray diffraction patterns reveal that orthorhombic Gd5Si4-type structure remains unchanged. The lattice parameters, unit cell volumes, and densities were estimated using the Rietveld least squares method. It showed that the lattice parameters decrease gradually in the (Gd_1-xR_x)₅Si₄(R=Dy,Ho) alloys with increasing Dy or Ho concentration. The results of magnetization versus temperature experiment show the Curie temperatures of (Gd_1-xRe_x)₅Si₄ systems are tunable continually from 336K to 260K and the desired Curie temperature can be obtained with the different R content. It was found that the Tc of the alloys decrease almost linearly with increasing x concentration. As a result, a formula used to estimate the Curie temperature was obtained. The magnetic phase transitions from the paramagnetic to the magnetically ordered state in all alloys are of the second order type. The magnetic entropy change in low magnetic fields (<20 kOe) retains a high value at Tc. The adiabatic temperature change values are obtained using the Control and Analysis System of the Adiabatic Temperature Changes Testing of Magnetic Refrigeratants. Although the adiabatic temperature change value of (Gd1-xRx)5Si4(R=Dy,Ho) alloys is approximately lower than that of Gd5Si4, the curves, which are 'caret-like'shape, of the adiabatic temperature change of (Gd1-xRx)5Si4(R=Dy,Ho) alloys are boarder than that of the latter. Although the maximum value of for each sample is lower than of that of pure Gd or approximately equal to that of Gd5Si4, its Tc can be adjusted by adding Dy or Ho concentration. The costs of the alloys are cheap because the raw materials are free from rather expensive element Ge. The magnetic entropy change and the adiabatic temperature change are in excellent consistent in low magnetic fields with the wide temperature range, so (Gd1-xRx)5Si4 alloys are suitable to be made the gradient function material. These suggest that the (Gd1-xRx)5Si4(R=Dy ,Ho) compounds are promising candidates for magnetic materials composites which may be used in the active magnetic regeneration refrigeration near room temperature in low magnetic fields.