INT | Nanostructured Materials

Magneto-Electronic Properties of HEM

This activity explores the vast magento-electronic phase space of HEM utilizing chemical disorder and strain engineering.
HEM Magneto-Eelectronic Properties Teaser
R. Kruk
Dr. Robert Kruk
Group Leader
Tunable Properties

+49 721 608-25916robert krukPun7∂kit edu

Radioactive and X-Ray Radiation Safety Officer 

Magnetic and correlated electronic properties in oxides systems are largely governed by exchange interactions, which depend upon the crystal structure, charge state and type of the metal cations that are hybridized with oxygen. In high entropy oxides (HEOs), there are numerous metal-oxygen-metal couples that are possible, which can lead to different and competing magnetic and electronic interactions. Thus the HEO based concept allows to access hitherto uncharted areas in the multicomponent magneto-electronic phase diagram. For instance, vertical exchange bias (VEB) that is typical of where heterogeneous structures is observed in single phase B-site disordered perovskite-HEOs. The VEB can be related to the high chemical disorder of the system stemming from competing magnetic interactions, which result in small ferromagnetic constellations in a predominant antiferromagnetic matrix. Alongside this, interesting magnetic features, such as noncollinearity, spin reorientation transitions, and large coercive fields of up to 2 T at ambient temperature are observed in A-site disordered perovskite-HEOs. These initial studies warrant further research in this directions.

Apart from the composition based property tailoring approach, strain-based engineering is also be employed in this research topic. HEOs are known to exhibit distinct inherent local distortions, which can be correlated to their physical properties. On top of that external strains can be applied via epitaxial thin film depositions, which will further allow probe the mageto-electronic phase space as a function of strain effects.

Lastly, magnetic properties, in general, are strongly related to the electronic structure and spin degrees of freedom, which in turn are also reflected by their optical characteristics. Therefore, optical properties, such as the band gap energies of the material are used as a quick diagnostic tool to have a preliminary understanding of the electronic structure.

Selected References
  • Magnetic properties of rare-earth and transition metal based perovskite type high entropy oxides R. Witte, A. Sarkar, L. Velasco, R. Kruk, R.A. Brand, B. Eggert, K. Ollefs, E. Weschke, H. Wende, H. Hahn, J. Appl. Phys. 2020, 127, 185109. DOI: 10.1063/5.0004125
  • Role of intermediate 4f states in tuning the band structure of high entropy oxides A. Sarkar, B. Eggert, L. Velasco, X. Mu, J. Lill, K. Ollefs, S.S. Bhattacharya, H. Wende, R. Kruk, R.A. Brand, H. Hahn, APL Mater. 2020, 8, 051111. DOI: 10.1063/5.0007944
  • High-entropy oxides: An emerging prospect for magnetic rare-earth transition metal perovskites R. Witte, A. Sarkar, R. Kruk, B. Eggert, R.A. Brand, H. Wende, H. Hahn, Phys. Rev. Mater. 2019, 3,034406. DOI: 10.1103/PhysRevMaterials.3.034406
  • Pressure-induced tuning of lattice distortion in a high-entropy oxide B. Cheng, H. Lou, A. Sarkar, Z. Zeng, F. Zhang, X. Chen, L. Tan, V. Prakapenka, E. Greenberg, J. Wen, R. Djenadic, H. Hahn, Q. Zeng, Commun. Chem. 2019, 2, 114. DOI: 10.1038/s42004-019-0216-2
  • Multicomponent equiatomic rare earth oxides with a narrow band gap and associated praseodymium multivalency A. Sarkar, C. Loho, L. Velasco, T. Thomas, S. S. Bhattacharya, H. Hahn, R. Djenadic Dalton Trans. 2017, 46, 12167-12176. DOI: 10.1039/C7DT02077E
Researchers Working on Magneto-Electric Properties of HEM
Portrait Name E-Mail Phone
richard brandTor3∂partner kit edu +49 721 608-26372
Horst Hahn
horst hahnJmg3∂kit edu +49 721 608-26351
R. Kruk
robert krukUkn1∂kit edu +49 721 608-25916
Abishek Sarkar
abhishek sarkarJzj1∂kit edu +49 721 608-28830
vladimir sepelakRst1∂kit edu +49 721 608-28929