A Study Of Structure And Magnetic Properties Of Novel Rare-Earth Transition Metal Intermetallic Compounds

The effects of Co substitution on the formation, structure and magnetic properties of the Nd3Fe29-x-y.COxMy (M=V, Cr) and Sm3Fe29-x-yCoxMoy compounds were investigated systemically by means of X-ray diffraction and magnetic measurement. The possibility of formation of the heavy rear-earth 3:29-type of compounds with Ho and Er was searched and the structure and magnetic properties of the corresponding compounds were investigated. In addition, the Nd2Co17. xVx compounds with V substitution for Co atom and (Nd1-xErx)2Co15.5V1.5 compound with Er substitution for Nd were also studied.A study on the Nd2Co17-xVx compounds shows that V substitution for Co results in a rapid decrease of the Curie temperature, the saturation magnetization and the Co average moments. The room temperature anisotropy changes from easy-plane-type for x<0.5 to easy-cone-type with 0.50.5, this may be related to the preferential occupation of V atoms on different Co sites. For a fixed V (1.5 atoms) and Co (15.5 atoms) content, substitution of Er for Nd results in a structural change and a change of the room temperature anisotropyThe Nd3Fe29-x-yCoxMy, (M=V, Cr) compounds were synthesized. X-ray diffraction and magnetic measurements show that Nd3Fe29-x-yCoxVy compounds with Nd3(Fe,Ti)29-type structure can only be synthesized up to x=12 and for x>12 no pure 3:29 phase can be obtained even by modifying the V content or the annealing temperature. All the compounds shows easy-plan type anisotropy at room temperature. The Co substitution for Fe leads to a drastic increase in Curie temperature and saturation magnetization. For the Nd3Fe29-x-yCoxCry compounds, the required Cr content to stabilize the 3:29 phase increases with increasing Co content. A pure Co-based Nd3Co21.5Cr7.5, was obtained. The Curie temperature and saturation magnetization increase first and then decrease with further increasing Co content. All the Nd3Fe29-x-yCoxCry compounds are all of easy-plan type anisotropy at room temperature.Sm3Fe28.1-xCoxMo0.9 compounds with x = 0, 4, 8, 12, 14, 16 have been synthesized. Substitution of Co for Fe leads to a significant increase in the Curie temperature and saturation magnetization, even more important, the easy magnetization direction changes from easy planetype to the easy axis type when x≥14. In this alloy system the compound Sm3Fe12.1Co16MO0.9 with the values of room-temperature saturation magnetization Ms = 1.5 T, anisotropy field Ba= 6.5 T and Curie temperature Tc = 1020 K, is a very promising candidate for permanent-magnet material.All the (Nd1-xErx)3Fe18Co6Cr5 compounds crystallize in Nd3(Fe,Ti)29-type structure till x≤0.8 The unit-cell volume and the Curie temperature decrease monotonically with increasing Er content. However, with further increasing Er content, a structure transformation was found. The new structure is different from the Nd3(Fe,Ti)29-type structure, but it still remains the main characteristics of the CaCus-type structure. The new phase is magnetically a single phase. The Curie temperature also shows an anomaly increase. A primal structure analysis shows that the new phase may belong to P3ml space group. At present, a further structure confirmation of the new structure is still in process.