Gd Substitution Effects on the Magnetic Properties of the Pr1−xGdxCo4Si Compounds
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- Kervan, N., Kervan, S. & Sözeri, H. J Supercond Nov Magn (2013) 26: 703. doi:10.1007/s10948-012-1789-5
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The crystal structure and magnetic properties of single phase Pr1−xGdxCo4Si compounds with x=0,0.2,0.4,0.6,0.8, and 1.0 have been investigated. X-ray analysis reveals that the compounds crystallize as a single phase having the hexagonal CaCu5-type structure with the space group P6/mmm. The substitution of Gd for Pr causes a linear decrease of the unit-cell parameters a and c, and the unit-cell volume V. Magnetic measurements indicate that all samples are ordered magnetically below the Curie temperature. The saturation magnetization at 4.2 K decreases upon the Gd substitution up to x=0.6, and then increases.
KeywordsMagnetic materialsX-ray diffractionMagnetic properties
The study of magnetic properties of rare-earth (R)-3d transition metals (T) intermetallic compounds is at present a topic in the physics of materials both for the technological aspect related to the possible discovery of new permanent magnets and for the scientific interest connected with the presence of complex magnetic behavior of the 4f and 3d elements [1–5]. The intermetallic compounds with general formula RT5 and their substitutional derivatives exhibit a variety of interesting properties such as high coercivity, crystal field effects, magnetocaloric effect, spin fluctuation, magnetic anisotropy, etc. [6–9]. The partial substitution for Co in the RCo5 compounds by non-magnetic elements with an outer p-shell, such as B, Al, C, Ga or Si atoms produces remarkable effects on the crystallographic and magnetic properties of the host compounds [10–12]. The RCo4Si compounds crystallize in the hexagonal CaCu5-type structure, with the space group P6/mmm. They are obtained by an ordered replacement of Co by Si in every second layer of the CaCu5 structure .
Previous investigations of the magnetic properties of RCo4Si compounds have evidenced that PrCo4Si is ferromagnetically ordered while in the case of GdCo4Si, a ferrimagnetic-type ordering was shown [13–15]. The Curie temperature TC and the saturation magnetization at 4.2 K are 425 K and 4.61μB/f.u. for PrCo4Si, 470 K and 2.76μB/f.u. for GdCo4Si, respectively . The compound GdCo4Si has also the compensation point Tcomp at 300 K .
In these compounds, the rare-earth sublattice couples either ferromagnetically or antiferromagnetically to the Mn sublattice in the case of light (Pr) or heavy rare earth (Gd), respectively. Therefore, it would be attractive to study the properties of the Pr1−xGdxCo4Si system to gain a deeper insight into magnetic interactions.
Polycrystalline Pr1−xGdxCo4Si compounds with x=0.0,0.2,0.4,0.6,0.8, and 1.0 were prepared by the arc melting technique under an argon atmosphere of appropriate amounts of Pr (99.9 %), Gd (99.9 %), Co (99.5 %) and Si (99.9999 %) in a water-cooled copper boat. In order to achieve good homogeneity, the polycrystalline ingots were inverted and remelted several times. X-ray diffraction studies were carried out by using a Brucker D8 Advance diffractometer equipped with CuKαradiation. The magnetic properties of the Pr1−xGdxCo4Si compounds were studied by means of a SQUID magnetometer (Quantum Design) in the temperature range 4–400 K in magnetic fields up to 5 T. Magnetic measurements were conducted with powder samples fixed in the sample holder. The temperature dependence of dc magnetization was measured in the zero-field cooling (ZFC) mode in 1 T. The value of the Curie temperature (TC) has been estimated from the minimum in the temperature derivative of the magnetization (dM/dT) versus temperature curve. The compensation temperature (Tcomp) was defined by the minimum appearing in the M–T curve.
3 Results and Discussion
It has been found from X-ray diffraction patterns at room temperature that
The lattice constants a and c, the unit-cell volume V,c/a, the saturation magnetization MS, the magnetic moment of the Co atom MCo, the compensation temperature and the Curie temperature TC for the Pr1−xGdxCo4Si compounds
The Pr1−xGdxCo4Si compounds with x=0,0.2,0.4,0.6,0.8, and 1.0 have been successfully synthesized. The crystalline structure has been refined from X-ray diffraction patterns using CuKα radiation. All compounds crystallize in the CaCu5-type structure. The substitution of Gd for Pr leads to linear decreases in the lattice constants and the unit-cell volume V. All compounds are ordered magnetically above room temperature. The compensation temperature Tcomp is seen at 152 K for x=0.8 and 326 K for x=1. The saturation magnetization at 4.2 K decreases upon the Gd substitution up to x=0.6, and then increases again.