Atomic-scale Structure and Its Correlation with Magnetic Properties of Rare-Earth Based Metallic Glasses

Description

In the past two decades, bulk metallic glass (BMG) has gradually evolved from a scientific curiosity to a family of engineering materials which possess unique combinations of properties and find applications as functional materials as well as structural materials. Such developments are resulted from numerous empirical investigations of properties augmented by fundamental examination of the atomic-level structures of metallic glasses. With the recent advent of experimental technique for probing atomic scale structure and numerical modeling systems, a lot of insights in structure-property relationship were reported, especially in areas concerning glass-forming ability and deformation behaviour of BMG.Magnetic metallic glasses are among the earliest group of MG which found industrial scale applications. Apart from the well known Fe-based MG, Gd-Fe MG was identified as a promising material for magnetic memory and magneto-optical applications. Gd-Co-Al BMG was also proposed for use as the working substance in magnetic refrigeration. However, detailed atomic-level structural information for these MG or BMG is not available. Scientifically, the interaction between a rare-earth element and a transition element can depend sensitively on the coordination number and the separation of the atoms, and therefore will exhibit a lot of intricate details in a glassy structure. Practically, better understanding of the relationship between local atomic structure and the macroscopic structure enables more efficient alloy design or development of thermal treatment for achieving desirable sets of properties of Gd-based BMG.The PI therefore proposed to investigate the relationship between cluster structure and magnetic properties of Gd-Co and Gd-Fe metallic glasses in a range of compositions which encompass alloys with different intermetallic phases. Local cluster structures are therefore expected to be similar to those of the intermetallic phases. The magnetic properties are also thought to show similarity with those of the corresponding crystalline phase, but slightly perturbed due to the deviation from the long-range order.Apart from the standard microstructure and thermal stability characterization, the PI will measure the magnetic properties of the MG samples using vibrating-sample magnetometer at temperature from ~2K to room temperature under a maximum field strength of 5T. In order to probe the atomic-scale structure of the MG samples, normal electron diffraction and nanobeam electron diffraction using an aberration-corrected transmission electron microscope. The PI also plans to liaise with a synchrotron-radiation facility in China for measuring the pair distribution functions of the samples to provide a overview of the statistical average properties.In order to augment the experimental investigation, numerical simulation of the amorphous structure will be carried out using commercially available software. The validity of the computed MG structure will be established by comparison with the experimentally measured structure factors and other structural parameters. Dominant structural units can then be identified in the computed structure. These results can provide invaluable information for understanding glass forming ability and other properties such as deformation behaviour of the Gd-based glass. Magnetic properties of the structure generated from simulation will be computed as well for comparison with experimental data. This is expected to give insight for the origin of the magnetic properties in these glassy alloys.When the project is completed, it is anticipated that a better understanding of the structure of (rare-earth)-(transition-metal)-based metallic glass as well as its correlation with magnetic properties can be obtained.