Tuning the magnetic properties from the design of nanoparticles with onion-like architecture

N. NUÑEZ; F. FABRIS; E. LIMA JR.; R.D. ZYSLER; M. AGUIRRE; E.L. WINKLER

Puerto Varas

Congreso; XII Latin American Workshop on Magnetism and Magnetic Materials (LAW3M2023); 2023

Universidad Central

One of the main challenges driving the development of nanostructured magnetic materials is the modulation of the magnetization response with a magnetic field. The magnetic inversion dynamics, and the magnitude of the coercive field, exchange bias field and the saturation magnetization determine the application range of each material, which should be tuned for different applications such as biomedicine or magneto-electronic. These parameters can be adjusted by combining compounds at the nanoscale with different magnetic characteristics. In particular, the onion-like architecture allows to combine in a single nanoparticle different components, with controlled size and high quality interfaces, opening a wide range of new possibilities. Here we will present different strategies followed to design and fabricate magnetic NPs with onion-like architecture in order to tune the magnetic anisotropy and the magnetic coupling between the different phases. In example, in exchange coupled systems the exchange bias field can be modulated by controlling the thickness of the oxidized shell in ~20 nm FeO/Fe3O4. Moreover, in ~10 nm Fe3O4/Co1−xZnxFe2O4 core/shell nanoparticles the magnetic anisotropy can be tuned by changing the shell composition, from 6.6x105 erg/cm3 for x=0, to 0.7x105 erg/cm3 for x=1.[1] On the other hand, by introducing a diamagnetic insulator between the ferrimagnetic phases the magnetic coupling can be modulated. In this case a ~22 nm Fe3O4 ferrimagnetic core was synthetized and afterward encapsulated by a first MgO shell of ~1nm thickness, and a second CoFe2O4 ferrimagnetic outer shell of ~2.5 nm thickness. [2] The magnetotransport of nanoparticles self-assembled arrays were measured, where the  switching field between the high and low resistant state can be tuning by the coercivity field of the systems. Finally, we will discuss the challenges still pending to achieve a fine-tune of the magnetic response in these complex nanostructures.[1] F. Fabris, Enio Lima Jr., C. Quinteros, L. Neñer, M. Granada, M. Sirena, R. D. Zysler, H.E. Troiani, V. Leborán, F. Rivadulla, and E. L. Winkler. Physical Review Applied 11, 054089 (2019).[2] J. M. Nuñez, S. Hettler, E. Lima Jr., G. F. Goya, R. Arenal, R. D. Zysler, M. H. Aguirre and E. L. Winkler. J. of Mat. Chem. C 10, 15339. (2022).