Transport properties of systematically disordered Cr2AlC films

Nano-lamellar composite materials, known as MAX-phases, can possess a combination of ceramic and metallic properties. A prototype compound is Cr2AlC, formed from a unit cell of Cr2C sandwiched between atomic planes of Al, thereby imparting a goodelectrical conductivity, as well as mechanical stability, radiationand oxidationresistance [1, 2]. Theseproperties rely on the lamellar structure of the compound, and systematic introduction of defects, such as displacing or doping atoms within the layers, has the potential to tune electron transport and modify magnetic properties. An ideal tool for defect implantation is ion-irradiation, available both in the form of a broad-beam for wafer-scale processing as well as focused ion-beams for device prototyping.Here we observe the modifications to the structural, transport and magnetic behavior of 500 nm thickCr2AlC afterirradiation with Co+ions, and Ar+noble gas ions as control. The films were irradiated with 450keV of Co+ions at fluences varying from 5E12 to 5E15 ions.cm-2, and the control samples with 400 keV Ar+ions keeping the sample fluences.Structural analysis using XRD shows that ion-irradiation induces asuppression of the 0002 reflection, indicating a gradual decay of the nano-lamellar structure, see Fig.1a. Increasing ion-fluence also leads toan increase of the saturation magnetizationat 1.5K, whereby both Ar+and Co+cause an increased magnetization, respectively to 150and 190 kA.m-1, for the highest fluences used.Large variations of the transport properties are observed(Fig. 1 b).Magnetoresistance (MR) in the non-irradiated sample shows a classical B2dependency, even up to high temperatures.At Co+fluences of 5E13ions.cm-2the MR at 10 T shows a 2 orders of magnitude increase, upto 3%(10 T)at 100 K, see Fig. 1b. A similar effect also occurs for 5E12ions.cm-2Ar+irradiated films, however with a smaller MR-increase.It appears that resistivity increases and the residual resistance ratio reduces with increasing fluence due to the introduction of disorder.Theseresults show that ion irradiation induces significant changes in the transport properties of MAX phase materials, that will be further investigated.The systematic disordering of nano-laminated MAX phase films may therefore reveal interesting disorder and spin-related transport phenomena.

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