94. Room Temperature Spin-Phonon Coupling in Cr2O3 Nanocrystals
Martín Testa-Anta, Julia N. Majcherkiewicz, Kai Xu, Alejandro R. Goñi, Verónica Salgueiriño
Advanced Functional Materials (2023), 2301973 (DOI: 10.1002/adfm.202301973).
In this study, nanocrystals of antiferromagnetic Cr2O3 are shown via Raman spectroscopy to display peculiar lattice dynamics in terms of phonon softening and the occurrence of an exceptionally strong spin-phonon coupling. This effect, which is observed to persist well above the onset of the antiferromagnetic ordering temperature, is ascribed to locally correlated spin fluctuations due to the modulation of the magnetic exchange interactions as the chromium atoms oscillate about their equilibrium position. We find that the spin-phonon coupling strength is governed by the competing antiferromagnetic and ferromagnetic interactions, where changes in the surface spin configuration can also play a crucial role. Overall, this work proves the size dependence of the interplay between the crystalline and magnetic structures in 3D antiferromagnets varying the surface-to-volume ratio, and helps establish the fundamentals for a spin-phonon coupling engineering at the nanoscale via a simple route in a very stable and easy to synthesize material. More importantly, it demonstrates the possibility of coupling phononic excitations with the magnetization dynamics at room temperature, offering a highly prospective nanomaterial for the design of novel magnonic devices.
93. Interfaceless exchange bias in CoFe2O4 Nanocrystals
Beatriz Rivas-Murias, Martín Testa-Anta, Alexander S. Skorikov, Miguel Comesaña-Hermo, Sara Bals, Verónica Salgueiriño
Nano Letters (2023), 23, 1688-1695 (DOI: 10.1021/acs.nanolett.2c04268).
Oxidized cobalt ferrite nanocrystals with a modified distribution of the magnetic cations in their spinel structure give place to an unusual exchange-coupled system with a double reversal of the magnetization, exchange bias and increased coercivity, but without the presence of a clear physical interface that delimits two well-differentiated magnetic phases. More specifically, the partial oxidation of cobalt cations and the formation of Fe vacancies at the surface region entail the formation of a cobalt-rich mixed ferrite spinel which is strongly pinned by the ferrimagnetic background from the cobalt ferrite lattice. This particular configuration of exchange-biased magnetic behavior, involving two different magnetic phases but without the occurrence of a crystallographically coherent interface, revolutionizes the established concept of the exchange bias phenomenology.
92. Nanoparticle biocoating to create ATP-powered swimmers capable of repairing proteins on the fly
Ana Rodríguez-Ramos, Miguel A. Ramos-Docampo, Verónica Salgueiriño, Mónica L. Fanarraga
Materials Today Advances (2023), 17, 100353 (DOI: 10.1016/j.mtadv.2023.100353).
In this study, a biocompatible self-propelled system based on the molecular chaperon Hsp90 is attained. This heat-shock protein (Hsp), in the presence of adenosine 5'-triphosphate (ATP), undegoes nanoscale conformational changes while trapping and renaturing other proteins, and therefore working as ATP-powered swimmers.
91. Magnetically propelled chained nanocomposites for biologically relevant media exploration
Miguel A. Ramos-Docampo, Pablo Hurtado, Ana B. Dávila-Ibáñez, Roberto Piñeiro, Mónica L. Fanarraga, Verónica Salgueiriño
Journal of Colloid and Interface Science (2023), 629, 287-296 (DOI: 10.1016/j.jcis.2022.08.154).
Elongated nanostructures to be remotely and magnetically propelled in biologically relevant media, have gained attention as offering themselves as effective tools or carriers in theragnostics applications. However, the magnetic actuation associated remains challenging due to the lack of mechanical information in the media of interest, taking into account biophysical or biomedical purposes. In this study, we detail the magnetic actuation of magnetically propelled chained nanocomposites considering their dynamics, in which their velocity can be modulated in terms of the viscosity of the medium considered, given a magnetic field gradient.
90. Magnetism Engineering in Antiferromagnetic β-FeOOH Nanostructures via Chemically Induced Lattice Deffects
Martín Testa-Anta, Ecem Tiryaki, Laura Bocher, Verónica Salgueiriño
Chemistry of Materials (2022), 34, 11026-11038 (DOI: 10.1021/acs.chemmater.2c03067).
Elongated akaganéite (β-FeOOH) nanostructures were synthesized through a simple hydrothermal route, in which a careful selection of the experimental conditions allows for a tunable length and aspect ratio and concomitantly predetermines the magnetic response. An in-depth structural characterization using transmission electron microscopy, X-ray diffraction, and Raman spectroscopy, jointly with DC magnetic measurements, reveals a complex scenario where the interstitial Cl- content dictates the β-FeOOH thermal stability and leads to the formation of bulk uncompensated spins along the inner channels. As a proof of concept, the β-FeOOH internal microstructure can be chemically manipulated through Cl- exchange, giving rise to a superparamagnetic component that comes along with an almost 20-fold increase in the coercivity at low temperature.
