BCMaterials Fortnightly Seminar #81 Rajasekhar Madugundo - José María Porro Azpiazu

RAJASEKHAR MADUGUNDO

(BCMATERIALS)

Development of alternative hard magnetic alloys to minimize the dependency on Rare-earth metals

Strong growth forecast in the green technology sectors such as electric vehicles, wind energy, also indicates an increase in the demand for permanent magnets. The magnets used for these applications are mainly rare-earth (RE) base and the increase in demand is going to put a huge pressure on the RE-metals industry which is already in crisis recently. Efforts are in progress to minimize the RE-dependency by developing magnets based on RE-free alloys and RE-lean alloys. Currently, we are working on development of RE-free Mn-Al-(C) based alloys and Sm-based RE-lean alloys. The alloys were prepared by melting the high pure elements or mechanically alloying the powders. The alloys were subjected to specific heat-treatment processes to obtain, stabilize and maximize the desired L1₀ tetragonal τ-phase in Mn Al-(C) alloys and tetragonal 1:12 phase in RE-lean alloys with high values of uniaxial anisotropy and saturation magnetization. The alloys then characterized for structural and magnetic properties. The alloys once optimized will be subjected to various processing methods such as milling, melt-spinning to develop coercivity. Selected alloys will be used for consolidation of bulk magnets

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JOSÉ MARÍA PORRO AZPIAZU

(BCMATERIALS)

Artificial Spin Ice Systems Far From Equilibrium: a Study of their Magnetization Dynamics

Artificial Spin Ice systems (ASIs)¹ are patterns of lithographically defined nanomagnets that mimic the behaviour of the spin-ice pyrochlores. The key ingredient of ASIs is that the nanomagnets forming the array have an Ising-like bistable uniform behaviour of their magnetization, therefore acting as macrospins disposed in geometries that lead to frustrated magnetic ground states. The modification of geometries, materials and/or sizes of the nanomagnets² provide us with a huge landscape of possibilities to explore the properties of ASIs. While the study of ASIs is of essential importance in the development of models for other frustrated systems in nature, they are also interesting from the applications point of view. The creation and flow of mobile magnetic charges (monopoles) that respond to externally applied magnetic fields³, the so-called “magnetricity”, is one of the interesting applications. In this talk I will give an introduction to the field of ASIs, and present our latest contributions in the study of the magnetization dynamics of these systems. More concretely, I will talk about the development of a synchrotron technique to probe the real-time magnetization dynamics of our ASIs⁴. Finally, I will speak about our findings of an unexpected negative correlation between their blocking temperature and interaction strength measured by SQUID magnetometry⁵.

¹ R.F. Wang RF, C. Nisoli, R.S. Freitas, J. Li, W. McConville, B.J. Cooley, M.S. Lund, N. Samarth, C. Leighton, V.H. Crespi, P. Schiffer, Nature 19; 439 (7074):303-6 (2006) ² J.M. Porro, A.Bedoya-Pinto, A. Berger, P. Vavassori, New J. Phys. 15 055012 (2013) ³ S.A. Morley, J.M. Porro, A. Hrabec, M.C. Rosamond, G. Burnell, M.Y. Im, P.J. Fischer, S. Langridge, C.H. Marrows, Manuscript in preparation (2017) ⁴ S.A. Morley, D.A. Venero, J.M. Porro, A. Stein, M.C. Rosamond, S.T. Riley, P. Steadman, S. Langridge, C.H. Marrows, Phys. Rev. B 95 104422 (2017) ⁵ J.M. Porro, S.A. Morley, D. Alba-Venero, R. Macedo, M.C. Rosamond, E.H. Linfield, R.L. Stamps, C.H. Marrows, S. Langridge, Manuscript under review (2017)