Unusual magnetic properties of the atomically laminated Mn₂GaC MAX phase

Iuliia Novoselova, University Duisburg-Essen, Duisburg, Germany
Andrejs Petruhins, Linköping University, Linköping, Sweden
Ulf Wiedwald, University Duisburg-Essen, Duisburg, Germany
Árni Sigurdur Ingason, Linköping University, Linköping, Sweden
Thomas Hase, University of Warwick, Coventry, United Kingdom
Fridrik Magnus, University of Iceland, Reykjavik, Iceland
Vassilios Kapaklis, Uppsala University, Uppsala, Sweden
Justinas Palisaitis , Linköping University, Linköping, Sweden
Marina Spasova, University Duisburg-Essen, Duisburg, Germany
Michael Farle, University Duisburg-Essen, Duisburg, Germany
Johanna Rosen, Linköping University, Linköping, Sweden
Ruslan Salikhov, University Duisburg-Essen, Duisburg, Germany

MAX phases (M_n+1AX_n, n = 1-3) are inherently nanolaminated hexagonal compounds, composed of early transition metals M, A-group elements and X (C or N). They possess unique anisotropic structural and physical properties showing ceramic as well as metallic response, such as thermal shock tolerance, oxidation resistance, and good electrical and thermal conductivity [1]. The magnetic ternary MAX phase, Mn2GaC, has been synthesized as a hetero-epitaxial film by magnetron sputtering [2].

Here, a comprehensive study of the temperature and field dependent magnetization, magnetoresistive (MR) and magnetostrictive (MS) properties is presented. The system exhibits two non-collinear antiferromagnetic states with a spin-reorientation transition occurring at Tt = 214 K and a high Neel temperature of TN = 507 K, where the system experiences a transition into a magnetically disordered state [3]. Among the yet discovered MAX phases, Mn₂GaC has the largest reported magnetic ordering temperature. A large uniaxial MS of 450 ppm at Tt in 2 Tesla was observed. The MS undergoes a sign change across the transition, being compressive (negative) above Tt and tensile (positive) below Tt. It is accompanied by a highly asymmetric MR of up to 3% in a magnetic field of 9 T at room temperature. The fact of simultaneous sign change of MS and MR indicates a strong coupling between the spin and lattice degrees of freedom. These magnetic properties open a pathway to new functionalities for practical applications.

This work is supported by DFG Grant SA 3095/2-1, DAAD Doctoral Programmes in Germany 2017/18 (57214224), Swedish Research Council (642-2013-8020) and the Swedish Foundation for Strategic Research (SSF) through the Synergy Grant FUNCASE.

References
[1] M. W. Barsoum, Prog. Solid State Chem. 28, 201 (2000).
[2] A. S. Ingason et al., Mater. Res. Lett. 2, 89-93 (2014).
[3] Iu.P. Novoselova et al., Scientific Reports 8, 2637 (2018).

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