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Dr. Primož Koželj (IJS, FMF): Magnetism of high-entropy alloys

Date of publication: 24. 2. 2022
Monday physics colloquium
Monday
28
February
Time:
16:15 - 17:15
Location:
Zoom
ID: 980 0889 5298
V ponedeljek, 28. 2. 2022, ob 16:15 prek Zooma

High-entropy alloys (HEAs) are a recent alloy design strategy [1], based on the fact that a high enthalpy of mixing will stabilize equimolar or near-equimolar solid solutions of four or more principal elements on very simple lattices, e.g. bcc or fcc. The popularity of the concept can be attributed to the very simple synthesis methods required (e.g. arc melting), the large number of options to try and design alloys for certain properties (adding, removing element, varying concentrations, thermal treatment) and from a basic science viewpoint to the interesting problems these systems pose as they contain interactions between four or more atomic species as well as micro- or nanostructural features.
The aim of this talk will be to present some interesting recent results in the magnetism of HEAs. Properly thermally treated FeCoNiPdCu is a soft magnetic material with a narrow hysteresis loop of coercivity cca 115 A/m, a high relative permeability of cca 3600 and a slightly enhanced electrical resistivity of 33.3 µΩcm [2], making it comparable to commercial magnetically soft materials for static and low-frequency applications. The soft magnetic properties are due to the composite nanostructure composed of magnetic FeCoNi-based domains and non-magnetic PdCu-based spacers.
We will also discuss a more homogenous system. The Co-Cr-Fe-Mn-Ni HEA [3] is a concentrated mixture of five types of magnetic atoms, where randomness and frustration lead to a spin glass phase below about 20 K, which we will illustrate via the non-ergodic phenomena of ultraslow decay of thermoremanent magnetization and the thermal memory effect (isothermal aging causes the system to remember its magnetic history upon cooling and this can be later retrieved during an upward temperature cycle).
[1] J.-W. Yeh et al., Adv. Eng. Mat. 6, 299 (2004).
[2] P. Koželj, S. Vrtnik, A. Jelen, M. Krnel, D. Gačnik, G. Dražić, A. Meden, M. Wencka, D. Jezeršek, D. Leskovec, S. Maiti, W. Steurer, J. Dolinšek, Adv. Eng. Mater. 21, 1801055 (2019).
[3] P. Koželj, S. Vrtnik, M. Krnel, A. Jelen, D. Gačnik, M. Wencka, Z. Jagličić, A. Meden, G. Dražić, F. Danoix, J. Ledieu, M. Feuerbacher, J. Dolinšek, J. Magn. Magn. Mater. 523, 167579 (2021).

https://uni-lj-si.zoom.us/j/98008895298