Transport and Magnetic Properties of Disordered Cr2AlC MAX Phases (TRANSMAX)

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Materials composed of two-dimensional layers of transition metal carbide or nitride molecules separated by layers of post-transition metal atoms, the so-called MAX phases, are well known for their outstanding mechanical properties and have found applications as high temperature coatings. Their nano-lamellar structure however, also has huge implications on the electronic transport, imparting a metal-like conductivity. Here we aim to investigate the potential of magnetically doped MAX phases for magneto-transport applications, leading to robust, temperature resistant mesoscopic devices. In continuation of the applications-focus, we select the Cr2AlC, an industrially-relevant MAX phase. In particular, we focus on the nano-lamellar structure, and deploy ion-irradiation to induce systematic changes to the structural ordering at the interface. Moreover we will apply ion-beam-doping using magnetic elements. Understanding of the above phenomena is necessary to identify and optimize MAX phases for magneto-transport. Energetic ions carrying magnetic moments, such as Co+, Mn+, Fe+ etc. will be used as magnetic dopants, whereas noble gas ions, such as Ar+ will be used to control the effects of disordering generated during the irradiation process. The degree of disordering can be controlled via the ion fluence and energy. Preliminary work shows that the sensitive disordering of the MAX interfaces, at ~0.1 Co+/nm2 fluence, can lead to a large enhancement of magneto-resistance, with a non-linear dependence of the overall resistance on the disorder. Pure disordering with Ar+ ions can also lead to increased magnetization, suggesting strong variation of the electronic structure through disorder. In our previous project, investigations on magnetically doped MAX phases have been made, with the aim of using the magnetization as an on-the-fly indicator of the integrity of the high-temperature coating. In the proposed 36-month project, a detailed investigation on commercially sourced MAX layers will be performed. Design and implementation of ion-irradiation and an investigation of its effects on the microstructure will be performed at the Ion Beam Centre (HZDR). In addition, low temperature transport measurements on lithographed transport devices will be performed at the TU Dresden. A shared PhD student will be trained on clean-room processes (HZDR) as well as in transport measurements (TUD). The insights gained on the Cr2AlC system may pave the way for applications of a variety of ion-disordered MAX phases as materials for magneto-transport.