Thermostability And Dielectric Properties In Tb-based And Gd-based Amorphous Alloys

It is widely known that metallic glasses are solid alloys exhibiting many superior properties to crystalline alloys. The unique properties originate from the random atomic arrangement of metallic glasses that contrasts with the regular atomic lattice arrangement found in crystalline alloys. A series of investigations on the glass-forming ability (GFA), structure and properties were carried out for various rare earth(RE)-based alloy systems and a number of RE-based bulk metallic glasses(BMG) were discovered in the Nd^-, Pr^-, Sm^-,Y^-, Ce^-, Mm(Mm=Ce+La+Pr+Nd)-based alloy systems. However, the known RE-based amorphous alloys have relatively low glass transition temperature Tg and crystallization temperature Tx which could limit some practical applications. Recently, some new kinds of heavy RE-based alloy systems were obtained mainly by Weihua Wang and his coworkers, among which, the Tb-, Gd-based alloy systems are of great importance for their high thermal stability and unique properties (e.g. magnetic and magneto-optical properties) and are attractive for applications as functional materials. On the other hand, previous theoretical studies predicted that the thermal stability of metallic glassed would be enhanced with the higher bulk modulus of the bade component, as heavy RE, Gd and Tb have relatively high bulk modulus and melting point, and low chemical activity in lanthanide family. Therefore, Tb^-, Gd-based alloy systems could have high thermal stability and unique properties, which are attractive for application as functional materials.In this thesis, a RE-based (RE=Tb,Gd) amorphous alloy system is reported. The ribbons of Tb₅₃Al₂₄Co₂₀Zr3,Tb33Er22Al25Co₂₀ and Gd₅₃Al₂₄Co₂₀Zr₃,Gd₃₃Er₂₂Al₂₅Co₂₀ amorphous alloys were prepared by a single roller melt-spinning method. Some experimental methods were utilized, such as x-ray diffraction (XRD), differential scanning calorimeter (DSC), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), etc. The systematic research work includes thermal stability and dielectric properties.Amorphous nature of the alloys was confirmed by SEM and XRD experiments. DSC experiments show the thermal stability of all the metallic glass. The supercooled liquid regions of Tb-based alloy are a little larger than that of Gd-based alloys. So the thermal stability of Tb-based alloys is better than Gd-based alloys. The results also show RE33Er22Al25Co₂₀(RE=Gd,Tb)have higher supercooled liquid region compared to RE₅₃Al₂₄Co₂₀Zr3, and thus RE33Er22Al25Co₂₀ ( RE=Gd,Tb ) are more stable. The Egami theory is applicable for all this samples. According to the theory, the thermal stability would be enhanced by a higher elastic modulus of the base element.The investigation of magnetic properties showed the Curie Temperature of Tb₅₃Al₂₄Co₂₀Zr3 is below 77K, whereas the Curie Temperature of Gd₅₃Al₂₄Co₂₀Zr3 is about 93K. The temperature dependent electrical resistance measurements were performed for the amorphous ribbons by usual four-probe method from 77K to 400K. A negative temperature coefficient of resistivity (TCR) is found for these amorphous samples. By means of flitting, the effective parameters of diffraction models,Mott s-d electronic dispersion, Two Level System diffraction (TLS), and Local Spin Fluctuation (LSF) were calculated in different temperature ranges.