Magnetische Anisotropie und Relaxation in einer neuen Materialklasse: Nanolaminierte magnetische MAX Phasen
Herstellung und Eigenschaften von Funktionsmaterialien
Zusammenfassung der Projektergebnisse
Inherently nanolaminated transition metal-based carbides, collectively known as MAX phases, attract tremendous interest due to their unique anisotropic structural and physical properties. MAX phases crystallize in a hexagonal structure with chemical composition Mn+1AXn (n = 1, 2, 3), where M is an early transition metal, A is a main group element and X is carbon. The layered, anisotropic crystal structure results in mechanical properties usually associated with ceramics, such as high stiffness, damage tolerance and resistance to corrosion and thermal shock. At the same time these materials shows metallic properties being electrically and thermally conductive. Combination of ceramic and metallic properties makes MAX phases useful for aerospace applications, heating elements, cutting tools, electrical switches, etc. Partial substitution of the M or A elements in the ternary compounds yields quaternary (Mx-1 1 Mx2)n+1ACn and Mn+1(Ax-1 1 Ax2)Cn phases with altered characteristics, extending the functional properties beyond those of the parent ternaries. Accordingly, a new class of magnetic MAX phases has been discovered by substitution of the M-element with Mn or rare earth (RE) elements. The new (Cr0.5Mn0.5)2GaC, (Mo0.5Mn0.5)2GaC and Mn2GaC MAX phases, stabilised in a thin film form, are chemically and compositionally stable at ambient conditions. Their decomposition temperature exceeds 800 K. All compounds show complex non-collinear antiferromagnetic structure due to the competing antiferromagnetic (AFM) and ferromagnetic (FM) interlayer exchange, which emerges at temperatures above 200 K. All magnetic phases possess the properties of a soft magnetic material with small magnetocrystalline anisotropy energy and small coercive field. These magnetic characteristics, however, can be substantially altered by substitution of the A elements. The films that were studied are electrically conductive and show moderate magnetoresistive characteristics, suggesting their applicability for spintronic elements and sensors. The main advantage of such elements is the fact that MAX phase materials do not oxidise or degrade, and that their surface and interface do not affect the magnetic properties of the film. This guarantees high functional stability even at unusual environments. Among all magnetic MAX phases, the Mn2GaC compound has the highest magnetic ordering temperature of 507 K. At this temperature, the system changes from the AFM state to the paramagnetic state. At the temperature of 214 K, the material undergoes a first order phase transition from a non-collinear AFM low spin state to a high spin state. Both magnetic states show large uniaxial c-axis magnetostriction of 450 ppm with sign inversion at the first order phase transition. The observed magnetostriction is the consequence of a field-induced magneto-structural transformation towards FM configuration. The sign change of magnetostriction coefficient across the phase transition is a new fundamental property, which is a consequence of the layered structure and competing AFM and FM exchange interactions between the magnetic atomic layers in Mn2GaC. Sign inversion is also found in magnetoresistance, suggesting a strong coupling among the spin, lattice and electrical transport properties. The observed properties suggest unique functionalities such as electrical detection of the magnetostriction in which the sign of the magnetoresistance depends on either compression or expansion of the material. 11 new (Mo2/3RE1/3)2AlC magnetic MAX phases, with the RE = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu, show magnetic order at temperature ranging from 3.6 K (for Er) to 28 K (for Tb). All compounds possess different no-collinear AFM structures with commensurate as well as incommensurate magnetic modulation of the RE moments. The magnetic structure as well as magnetic ordering temperature and effective magnetic moment are strongly depended on the choice of the RE element. The in-plane as well as out-of-plane chemical ordering of RE atoms, competing exchange interaction and spin-orbit coupling result plethora of magnetic ground states in these compounds, which can host magnetic frustrated states and exotic excitations.
Projektbezogene Publikationen (Auswahl)
- Thin film synthesis and characterization of a chemically ordered magnetic nanolaminate (V,Mn) 3GaC2. APL Materials 4, 086109 (2016)
Q. Tao, R. Salikhov, A. Mockute, J. Lu, M. Farle, U. Wiedwald, and J. Rosen
(Siehe online unter https://doi.org/10.1063/1.4961502) - Magnetic properties of nanolaminated (Mo0.5Mn0.5)2GaC MAX phase. J. Appl. Phys. 121, 163904 (2017)
R. Salikhov, R. Meshkian, D. Weller, B. Zingsem, D. Spoddig, J. Lu, A. S. Ingason, H. Zhang, J. Rosen, U. Wiedwald, M. Farle
(Siehe online unter https://doi.org/10.1063/1.4982197) - Large uniaxial magnetostriction with sign inversion at the first order phase transition in the nanolaminated Mn2GaC MAX phase. Scientific Reports 8, 2637 (2018)
Iu. P. Novoselova, A. Petruhins, U. Wiedwald, A. S. Ingason, T. Hase, F. Magnus, V. Kapaklis, J. Palisaitis, M. Spasova, M. Farle, J. Rosen, and R. Salikhov
(Siehe online unter https://doi.org/10.1038/s41598-018-20903-2) - Magnetic properties and structural characterization of layered (Cr 0.5Mn0.5)2AuC synthesized by thermally induced substitutional reaction in (Cr0.5Mn0.5)2GaC. APL Materials 6, 026104 (2018)
C. C. Lai, Q. Tao, H. Fashandi, U. Wiedwald, R. Salikhov, M. Farle, A. Petruhins, J. Lu, L. Hultman, P. Eklund, and J. Rosen
(Siehe online unter https://doi.org/10.1063/1.5006304) - Structural, magnetic and electrical transport properties of non-conventionally prepared MAX phases V2AlC and (V/Mn)2AlC. Mater. Chem. Front. 2, 483-490 (2018)
C. M. Hamm, M. Dürrschnabel, L. Molina-Luna, R. Salikhov, D. Spoddig, M. Farle, U. Wiedwald, and C. Birkel
(Siehe online unter https://doi.org/10.1039/c7qm00488e) - Atomically layered and ordered rare-earth i-MAX phases: a new class of magnetic quaternary compounds. Chem. Mater. 31, 2476-2485 (2019)
Q. Tao, J. Lu, M. Dahlqvist, A. Mockute, S. Calder, A. Petruhins, R. Meshkian, O. Rivin, D. Potashnikov, E. N. Caspi, H. Shaked, A. Hoser, C. Opagiste, R.-M. Galera, R. Salikhov, U. Wiedwald, C. Ritter, A. R. Wildes, B. Johansson, L. Hultman, M. Farle, M. W. Barsoum, J. Rosen
(Siehe online unter https://doi.org/10.1021/acs.chemmater.8b05298) - Long-term stability and thickness dependence of magnetism in thin (Cr0.5Mn0.5)2GaC MAX phase films. Mater. Res. Lett. 7, 159-163 (2019)
Iu. P. Novoselova, A. Petruhins, U. Wiedwald, D. Weller, J. Rosen, M. Farle, and R. Salikhov
(Siehe online unter https://doi.org/10.1080/21663831.2019.1570980)
