Addressing Criticality in Rare Earth Elements via Permanent Magnets Recycling

Rare earth elements (REEs) are critical for many advanced technologies and are faced with potential supply disruptions. Recycling of permanent magnets (PMs) can be good sources for REEs which can help minimize global dependence on freshly mined REEs, but PMs are rarely recycled. Recycling of PMs has been discussed with respect to improving REEs resource sustainability. Some challenges to be addressed in order to establish industrially deployable technologies for PMs recycling have also been discussed, including profitability, energy efficiency and environmental impacts. Key considerations for promoting circular economy via PMs recycling is proposed with the focus on deciding the target points in the supply chain at which the recycled products will be inserted. Important technical considerations for recycling different forms of waste PMs, including swarfs, slags, shredded and intact hard disk drives magnets, have been presented. The aspects of circular economy considered include reusing magnets, remanufacturing magnets and recovering of REEs from waste PMs

A model for the Barkhausen frequency spectrum as a function of applied stress

We derive a two parameter multi-exponential model to describe the frequency spectrum ofBarkhausen noise in bulk steel under high excitation rates and applied tensile stress. We show how the amplitude and shape of the frequency spectrum depend on two directly measurable quantities, Barkhausen voltage and effective magnetic permeability, respectively, and how these change with stress. By incorporating frequency and depth dependence components into our model, we provide a framework for identifying stress variations along depth, which can be used for the purposes of non-destructive characterization

Microstructure and Magnetic Properties of Grain Refined Pr2Co14B Melt-Spun Ribbons

The correlation between the grain refining effect of TiC on the microstructure of Pr2Co14B melt-spun ribbons and the magnetic properties is presented in this study. TiC enabled greater control of microstructure both in the as-spun and heat treated Pr2Co14B, compared with the material without TiC. As a result, coercivity of the sample with TiC was nearly twice that of the sample without TiC. In addition to Pr2Co14B, two other phases were found in the sample with TiC: one rich in Co and the other having a composition near PrCo2. TiC was found near the grain boundaries and at triple junctions. Also no Ti or C was found in the matrix phase indicating extreme low solubility of the elements when both are present with Pr2Co14B. As expected, both the samples with and without TiC have similar anisotropy field but the presence of room temperature non-ferromagnetic phases (TiC and PrCo2), caused a small decrease in magnetization of the sample with TiC although the romance of the isotropic materials were comparable

Optimization of sensor design for Barkhausen noise measurement using finite element analysis

The effects of design parameters for optimizing the performance of sensors for magneticBarkhausen emission measurement are presented. This study was performed using finite element analysis. The design parameters investigated include core material, core-tip curvature, core length, and pole spacing. Considering a combination of permeability and saturation magnetization, iron was selected as the core material among other materials investigated. Although a flat core-tip would result in higher magnetic flux concentration in the test specimen, a curved core-tip is preferred. The sensor-to-specimen coupling is thereby improved especially for materials with different surface geometries. Smaller pole spacing resulted in higher flux concentration