Structural Stability And Dilute Magnetic Effect Of Minor Co-doped Rare-Earth In-based 1:3 Compounds

The starting alloys with the nominal compositions of RIn3-x,COx were prepared using Arc melting in an atmosphere of Argon gas.The planar indices were determined with a TREOR program.The lattice parameters and unit cell volumes were determined.The crystal structures and atomic occupations were determined using a Rietveld structural refinement technology.The SQUID and VSM were used to investigate the magnetic properties.The refined results reveal that the main phase of RIn3-xCox crystallize cubic structure with a group space of Pm-3m and Z=1.The rare earth atoms occupy the la position,indium atoms are at the 3c sites.The doping element cobalt prefers to occupy the 3c crystal position.However,the substitution of Co for Dy is found in DyIn3-xCox alloys.The second phase induced by Co doping into RIn3 has been observed in RIn3xCox and its structure is determined based on a structural model of hexagonal cell with the space group of P63/mmc and Z=2.The structural formula is PrIn2-xCox.There are two nonequivalent crystal positions in one unit cell,i.e.,2b and 4f crystal positions,which are occupied by 2Pr and 4(In,Co),respectively.Co atoms prefer to occupy the 4f position.It implies that RIn2 phase could be stabilized by the small amount doping of cobalt.The results show the magnetic properties of PrIn3-xCox and NdIn3-xCox are very sensitive to Co content.Co doping into PrIn3 and NdIn3 induce the formation of ferromagnetic phase at room temperature.With increasing Co content,the magnetic phases exhibit a transition from paramagnetic to a mixture of ferromagnetic and paramagnetic to ferromagnetic,respectively.with increasing Co contents in RIn3-xCox(R=Pr,Nd),the susceptibility X decrease and Ms increase.A mixture of ferromagnetic and paramagnetic has been observed in GdIn3-xCox and TbIn3-xCOx.With increasing Co content,the magnetic phases exhibit a transition from paramagnetic to a mixture of ferromagnetic and paramagnetic to paramagnetic,respectively.However,DyIn3_xCox show paramagnetic at room temperature.RIn3-xCox order antiferromagnetically at low temperature.The main phase of RIn2.9Co0.1 crystallize in cubic structure with space group of Pm-3m and Z=1.The lattice parameters and unit cell volumes decrease with atomic number of R increasing.This results in the shrinkage of the atomic radius with atomic number of R increasing.The phase transition in RIn3-xCox is suspected to be driven by the atomic size effect or electronegativity.