Unraveling dissipation-related features in magnetic imaging by bimodal magnetic force microscopy

Magnetic Force Microscopy (MFM) is the principal characterization technique for the study of low-dimensional magnetic materials. Nonetheless, during years, the samples under study was limited to samples in the field of data storage, such as longitudinal hard disk, thin films, or patterned nanostructures. Nowadays, thanks to the advances and developments in the MFM modes and instrumentation, other fields are emerging like skyrmionic structures, 2D materials or biological samples. However, in these experiments artifacts in the magnetic images can have strong impact and need to be carefully verified for a correct interpretation of the results. For that reason, in this paper we will explore new ideas combining the multifrequency modes with the information obtained from the experimental dissipation of energy associated to tip-sample interaction

Procesos de imanacion en la nanoescala mediante microscopia de fuerzas magneticas

Tesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 27-02-200

An upper bound for the magnetic force gradient in graphite

Cervenka et al. have recently reported ferromagnetism along graphite steps. We present Magnetic Force microscopy (MFM) data showing that the signal along the steps is independent of an external magnetic field. Moreover, by combining Kelvin Probe Force Microscopy (KPFM) and MFM, we are able to separate the electrostatic and magnetic interactions along the steps obtaining an upper bound for the magnetic force gradient of about16 microN/m, a figure six times lower than the lowest theoretical bound reported by Cervenka et al. Our experiments suggest absence of MFM signal in graphite at room temperature.Comment: 14 pages, including supplemetary informatio

Improved graphene blisters by ultrahigh pressure sealing

Graphene is a very attractive material for nanomechanical devices and membrane applications. Graphene blisters based on silicon oxide micro-cavities are a simple but relevant example of nanoactuators. A drawback of this experimental set up is that gas leakage through the graphene-SiO2 interface contributes significantly to the total leak rate. Here we study the diffusion of air from pressurized graphene drumheads on SiO2 micro-cavities and propose a straightforward method to improve the already strong adhesion between graphene and the underlying SiO2 substrate, resulting in reduced leak rates. This is carried out by applying controlled and localized ultrahigh pressure (> 10 GPa) with an Atomic Force Microscopy diamond tip. With this procedure, we are able to significantly approach the graphene layer to the SiO2 surface around the drumheads, thus enhancing the interaction between them allowing us to better seal the graphene-SiO2 interface, which is reflected in up to ~ 4 times lower leakage rates. Our work opens an easy way to improve the performance of graphene as a gas membrane on a technological relevant substrate such as SiO2.Comment: pages 19, 4 figures + supplementary informatio

Stripe domains in electrodeposited Ni90Fe10 thin films

Here we have investigated the formation of stripe domains in electrodeposited Ni90Fe10 films, a metallic alloy with relevant magnetoelastic properties. The X-ray diffractometry patterns confirm the deposition of NiFe with an experimental lattice parameter close to the theoretical value. We have analyzed the influence of both magnetic stirring and an applied magnetic field perpendicular to the sample plane on the formation of stripe domains in Ni90Fe10 films. It is observed the characteristic fingerprint of stripe domains, i.e. the transcritical shape in the in-plane hysteresis loops when the electrolyte is not magnetically stirred during electrodeposition. The quality factor reveals a moderate perpendicular magnetic anisotropy which is confirmed by the stripe periodicity inferred by Magnetic Force Microscopy. In particular, stripe domains are only visible by this technique when the sample thickness is well above the theoretical critical thickness for the stripe domains to be formed. Finally, in samples released after being grown in outward bent flexible substrates it has been promoted an induced in-plane magnetoelastic magnetic anisotropy that reduces the perpendicular magnetic anisotropy. The high quality of the samples studied in this work from the magnetoelastic point of view is reflected by the magnetostriction constant of −22 ppm that it has been experimentally inferre

3D quasi-skyrmions in thick cylindrical and dome-shape soft nanodots

Magnetic skyrmions are widely attracting researchers due to fascinating physics and novel applications related to their non-trivial topology. Néel skyrmions have been extensively investigated in magnetic systems with Dzyaloshinskii–Moriya interaction (DMI) and/or perpendicular magnetic anisotropy. Here, by means of micromagnetic simulations and analytical calculations, we show that 3D quasi-skyrmions of Néel type, with topological charge close to 1, can exist as metastable states in soft magnetic nanostructures with no DMI, such as in Permalloy thick cylindrical and dome-shaped nanodots. The key factor responsible for the stabilization of DMI-free is the interplay of the exchange and magnetostatic energies in the nanodots. The range of geometrical parameters where the skyrmions are found is wider in magnetic dome-shape nanodots than in their cylindrical counterparts. Our results open the door for a new research line related to the nucleation and stabilization of magnetic skyrmions in a broad class of nanostructured soft magnetic materials

3D quasi-skyrmions in thick cylindrical and dome-shape soft nanodots.

[EN] Magnetic skyrmions are widely attracting researchers due to fascinating physics and novel applications related to their non-trivial topology. Néel skyrmions have been extensively investigated in magnetic systems with Dzyaloshinskii–Moriya interaction (DMI) and/or perpendicular magnetic anisotropy. Here, by means of micromagnetic simulations and analytical calculations, we show that 3D quasi-skyrmions of Néel type, with topological charge close to 1, can exist as metastable states in soft magnetic nanostructures with no DMI, such as in Permalloy thick cylindrical and dome-shaped nanodots. The key factor responsible for the stabilization of DMI-free is the interplay of the exchange and magnetostatic energies in the nanodots. The range of geometrical parameters where the skyrmions are found is wider in magnetic dome-shape nanodots than in their cylindrical counterparts. Our results open the door for a new research line related to the nucleation and stabilization of magnetic skyrmions in a broad class of nanostructured soft magnetic materials.E.B. acknowledges the Alexander von Humboldt foundation for a postdoctoral fellowship. M.J. acknowledges the Universidad Autónoma de Madrid and Comunidad Autónoma de Madrid through the project SI1/PJI/2019-00055 and the program “Excelencia para el Profesorado Universitario”, as well as the María de Maeztu Programme for Units of Excellence in R&D (CEX2018-000805-M). K.G. acknowledges support by IKERBASQUE (the Basque Foundation for Science). O.C., A.A. and K.G. work was supported by the Spanish Ministry of Science and Innovation under Grants PID2019-108075RB-C31 and PID2019-108075RB-C33/AEI/https://doi.org/10.13039/501100011033. The research of K.G. was partially supported by the Norwegian Financial Mechanism 2014–2021 trough project UMO-2020/37/K/ST3/02450. Open Access funding enabled and organized by Projekt DEAL

Hysteresis loops of individual Co nanostripes measured by magnetic force microscopy

High-resolution magnetic imaging is of utmost importance to understand magnetism at the nanoscale. In the present work, we use a magnetic force microscope (MFM) operating under in-plane magnetic field in order to observe with high accuracy the domain configuration changes in Co nanowires as a function of the externally applied magnetic field. The main result is the quantitative evaluation of the coercive field of the individual nanostructures. Such characterization is performed by using an MFM-based technique in which a map of the magnetic signal is obtained as a function of both the lateral displacement and the magnetic field

Improved graphene blisters by ultrahigh pressure sealing

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Materials and Interfaces, copyright © American Chemical Society after peer review and technical editing by the publisher. To acces final work see “Improved Graphene Blisters by Ultrahigh Pressure Sealing”, ACS Applied Materials and Interfaces 12.33 (2020): 37750-37756, 10.1021/acsami.0c09765Graphene is a very attractive material for nanomechanical devices and membrane applications. Graphene blisters based on silicon oxide microcavities are a simple but relevant example of nanoactuators. A drawback of this experimental setup is that gas leakage through the graphene-SiO2 interface contributes significantly to the total leak rate. Here, we study the diffusion of air from pressurized graphene drumheads on SiO2 microcavities and propose a straightforward method to improve the already strong adhesion between graphene and the underlying SiO2 substrate, resulting in reduced leak rates. This is carried out by applying controlled and localized ultrahigh pressure (>10 GPa) with an atomic force microscopy diamond tip. With this procedure, we are able to significantly approach the graphene layer to the SiO2 surface around the drumheads, thus enhancing the interaction between them, allowing us to better seal the graphene-SiO2 interface, which is reflected in up to ∼4 times lower leakage rates. Our work opens an easy way to improve the performance of graphene as a gas membrane on a technological relevant substrate such as SiO2We acknowledge financial support from the Spanish Ministry of Science and Innovation, through the “Marı́ ́ a de Maeztu” Programme for Units of Excellence in R&D (CEX2018- 000805-M), projects PID2019-106268GB, S2018/NMT-451, and FLAG-ERA JTC2017, and the Ramon Areces Foundation. G.L.-P. acknowledges financial support through the “Juan de la Cierva” Fellowship FJCI-2017-3237