Special Issue "Magnetic and Magnetoelectric Nanomaterials: Synthesis, Characterization and Applications"

A special issue of Nanomaterials (ISSN 2079-4991). This special issue belongs to the section "Nanofabrication and Nanomanufacturing".

Deadline for manuscript submissions: closed (31 August 2021).

Special Issue Editors

Prof. Dr. João Pedro Araujo
E-Mail Website
Guest Editor
Department of Physics and Astronomy, Universidade do Porto, 4099-002 Porto, Portugal
Interests: Nanomaterials; Magnetic Nanomaterials; Template based synthesis; Van der Walls materials; Energy Harvesting; Solar and Photoelectrochemical Cells; Electronic structure methods; Hyperfine Methods
Dr. Armandina Lopes
E-Mail Website
Guest Editor
Institute of Physics for Advanced Materials, Nanotechnology and Photonics (IFIMUP), department of Physics and Astronomy, faculty of Sciences, University of Porto, 4169-007 Portio, Portugal
Interests: condensed matter physics; complex oxides; magnetism; multiferroics; magnetoelectrics; density functional theory; local probing; hyperfine interaction

Special Issue Information

Dear Colleague,

Functional nanomaterials and nanostructures occupy central importance in nowadays technologies, nonetheless, offer still significant new opportunities in different fields. In particular, magnetic and magnetoelectric nanomaterials can bring innovative solutions for applications in energy harvesting, spintronics, sensing and biosensing applications. Moreover, their unique functional properties offer a vast playground for fundamental science and materials engineering.

This Special Issue welcome both theoretical and experimental approaches, namely by including the design of new magnetic and magnetoelectric nanomaterials using computational screening methods based on genetic algorithms, combined with density functional theory, and/or their synthesis and characterization, towards the development of material architectures for applications, especially for the areas of energy, information technology and sensing aiming to solve emergent societal challenges.

Prof. Dr. João Pedro Araujo
Dr. Armandina Lopes
Guest Editors

Manuscript Submission Information

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Keywords

  • New functional nanomaterials
  • Energy Harvesters
  • Magnetoelectric Random Access Memory
  • Magnetic Recording Read Head
  • Magnetic Field Sensors
  • Biomedical Applications
  • Biosensors

Published Papers (6 papers)

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Research

Article
Growth and Characterisation Studies of Eu3O4 Thin Films Grown on Si/SiO2 and Graphene
Nanomaterials 2021, 11(6), 1598; https://doi.org/10.3390/nano11061598 - 17 Jun 2021
Viewed by 517
Abstract
We report the growth, structural and magnetic properties of the less studied Eu-oxide phase, Eu3O4, thin films grown on a Si/SiO2 substrate and Si/SiO2/graphene using molecular beam epitaxy. The X-ray diffraction scans show that highly textured [...] Read more.
We report the growth, structural and magnetic properties of the less studied Eu-oxide phase, Eu3O4, thin films grown on a Si/SiO2 substrate and Si/SiO2/graphene using molecular beam epitaxy. The X-ray diffraction scans show that highly textured crystalline Eu3O4(001) films are grown on both substrates, whereas the film deposited on graphene has a better crystallinity than that grown on the Si/SiO2 substrate. The SQUID measurements show that both films have a Curie temperature of ∼5.5±0.1 K, with a magnetic moment of ∼320 emu/cm3 at 2 K. The mixed valence of the Eu cations has been confirmed by the qualitative analysis of the depth-profile X-ray photoelectron spectroscopy measurements with the Eu2+:Eu3+ ratio of 28:72. However, surprisingly, our films show no metamagnetic behaviour as reported for the bulk and powder form. Furthermore, the microscopic optical images and Raman measurements show that the graphene underlayer remains largely intact after the growth of the Eu3O4 thin films. Full article
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Article
Control of Structural and Magnetic Properties of Polycrystalline Co2FeGe Films via Deposition and Annealing Temperatures
Nanomaterials 2021, 11(5), 1229; https://doi.org/10.3390/nano11051229 - 07 May 2021
Viewed by 554
Abstract
Thin polycrystalline Co2FeGe films with composition close to stoichiometry have been fabricated using magnetron co-sputtering technique. Effects of substrate temperature (TS) and post-deposition annealing (Ta) on structure, static and dynamic magnetic properties were systematically studied. It is [...] Read more.
Thin polycrystalline Co2FeGe films with composition close to stoichiometry have been fabricated using magnetron co-sputtering technique. Effects of substrate temperature (TS) and post-deposition annealing (Ta) on structure, static and dynamic magnetic properties were systematically studied. It is shown that elevated TS (Ta) promote formation of ordered L21 crystal structure. Variation of TS (Ta) allow modification of magnetic properties in a broad range. Saturation magnetization ~920 emu/cm3 and low magnetization damping parameter α ~ 0.004 were achieved for TS = 573 K. This in combination with soft ferromagnetic properties (coercivity below 6 Oe) makes the films attractive candidates for spin-transfer torque and magnonic devices. Full article
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Article
Group Theory Analysis to Study Phase Transitions of Quasi-2D Sr3Hf2O7
Nanomaterials 2021, 11(4), 897; https://doi.org/10.3390/nano11040897 - 31 Mar 2021
Cited by 1 | Viewed by 766
Abstract
We present an ab-initio study performed in the framework of density functional theory, group-subgroup symmetry analysis and lattice dynamics, to probe the octahedral distortions, which occur during the structural phase transitions of the quasi-2D layered perovskite Sr3Hf2O7 compound. [...] Read more.
We present an ab-initio study performed in the framework of density functional theory, group-subgroup symmetry analysis and lattice dynamics, to probe the octahedral distortions, which occur during the structural phase transitions of the quasi-2D layered perovskite Sr3Hf2O7 compound. Such a system is characterized by a high-temperature I4/mmm centrosymmetric structure and a ground-state Cmc21 ferroelectric phase. We have probed potential candidate polymorphs that may form the I4/mmmCmc21 transition pathways, namely Fmm2, Ccce, Cmca and Cmcm. We found that the band gap widths increase as the symmetry decreases, with the ground-state structure presenting the largest gap width (∼5.95 eV). By probing the Partial Density of States, we observe a direct relation regarding the tilts and rotations of the oxygen perovskite cages as the transition occurs; these show large variations mostly of the O p-states which contribute mostly to the valence band maximum. Moreover, by analyzing the hyperfine parameters, namely the Electric Field Gradients and asymmetric parameters, we observe variations as the transition occurs, from which it is possible to identify the most plausible intermediate phases. We have also computed the macroscopic polarization and confirm that the Cmc21 phase is ferroelectric with a value of spontaneous polarization of 0.0478 C/m2. The ferroelectricity of the ground-state Cmc21 system arises due to a second order parameter related to the coupling of the rotation and tilts of the O perovskite cages together with the Sr displacements. Full article
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Article
Formation of Nickel Oxide Nanocuboids in Ferromagnetic La2Ni1−xMn1+xO6
Nanomaterials 2021, 11(3), 804; https://doi.org/10.3390/nano11030804 - 21 Mar 2021
Viewed by 531
Abstract
The control of the spontaneous formation of nanostructures at the surface of thin films is of strong interest in many different fields, from catalysts to microelectronics, because surface and interfacial properties may be substantially enhanced. Here, we analyze the formation of nickel oxide [...] Read more.
The control of the spontaneous formation of nanostructures at the surface of thin films is of strong interest in many different fields, from catalysts to microelectronics, because surface and interfacial properties may be substantially enhanced. Here, we analyze the formation of nickel oxide nanocuboids on top of La2Ni1−xMn1+xO6 double perovskite ferromagnetic thin films, epitaxially grown on SrTiO3 (001) substrates by radio-frequency (RF) magnetron sputtering. We show that, by annealing the films at high temperature under high oxygen partial pressure, the spontaneous segregation of nanocuboids is enhanced. The evolution of the structural and magnetic properties of the films is studied as a function of the annealing treatments at different temperatures. It is shown that the formation of NiOx nanocuboids leads to a nanostructured film surface with regions of locally different electrical transport characteristics. Full article
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Article
Room Temperature Magnetic Memory Effect in Nanodiamond/γ-Fe2O3 Composites
Nanomaterials 2021, 11(3), 648; https://doi.org/10.3390/nano11030648 - 07 Mar 2021
Viewed by 674
Abstract
We report a room temperature magnetic memory effect (RT-MME) from magnetic nanodiamond (MND) (ND)/γ-Fe2O3 nanocomposites. The detailed crystal structural analysis of the diluted MND was performed by synchrotron radiation X-ray diffraction, revealing the composite nature of MND having 99 and [...] Read more.
We report a room temperature magnetic memory effect (RT-MME) from magnetic nanodiamond (MND) (ND)/γ-Fe2O3 nanocomposites. The detailed crystal structural analysis of the diluted MND was performed by synchrotron radiation X-ray diffraction, revealing the composite nature of MND having 99 and 1% weight fraction ND and γ-Fe2O3 phases, respectively. The magnetic measurements carried out using a DC SQUID magnetometer show the non-interacting superparamagnetic nature of γ-Fe2O3 nanoparticles in MND have a wide distribution in the blocking temperature. Using different temperature, field, and time relaxation protocols, the memory phenomenon in the DC magnetization has been observed at room temperature (RT). These findings suggest that the dynamics of MND are governed by a wide distribution of particle relaxation times, which arise from the distribution of γ-Fe2O3 nanoparticle size. The observed RT ferromagnetism coupled with MME in MND will find potential applications in ND-based spintronics. Full article
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Article
Temperature Dependence and Microstructure Effects on Magnetic Properties of FePt(B, Ag, C) Film
Nanomaterials 2021, 11(2), 419; https://doi.org/10.3390/nano11020419 - 07 Feb 2021
Viewed by 502
Abstract
A FePt(B, Ag, C) granular film was formed from post-annealed B4C(1.0 nm)/FePt(Ag, C) layers at a substrate temperature of 470 °C for 2 min. The 6 nm thick FePt(B, Ag, C) film demonstrates high perpendicular magnetic anisotropy (Ku = 2.83 [...] Read more.
A FePt(B, Ag, C) granular film was formed from post-annealed B4C(1.0 nm)/FePt(Ag, C) layers at a substrate temperature of 470 °C for 2 min. The 6 nm thick FePt(B, Ag, C) film demonstrates high perpendicular magnetic anisotropy (Ku = 2.83 × 107 erg/cm3 at 100 K) and out-of-plane coercivity (Hc = 38.0 kOe at 100 K). The Ku and out-of-plane Hc are respectively increased from 38% and 46% between 350 K and 50 K. The sample with a thickness of 8 nm also shows a similar trend for magnetic properties; however, the tiny magnetization kink which may come from rare Fe-B or disordered FePt grains was observed in the easy axis loop. The intrinsic (ΔHint = 12.6 kOe) and extrinsic switching field distribution (ΔHext = 1.62 kOe) were characterized by major and minor loops to correlate the microstructural grains. The coupled FePt grains grown on a single MgTiON grain were observed in a high-resolution transmission electron microstructure (HRTEM) image. This small intergranular exchange coupling was defined by estimating the magnetic cluster size (46.6 nm) from ΔHext and the average grains size (28.2 nm) from TEM images. The temperature dependence of coercivity was fitted to further understand the magnetization reversal process. The lower microstructural parameter was evidenced in the imperfect grain morphology. Full article
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