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Tunable room-temperature ferromagnet using an iron-oxide and graphene oxide nanocomposite.

Lin AL, Rodrigues JN, Su C, Milletari M, Loh KP, Wu T, Chen W, Neto AH, Adam S, Wee AT - Sci Rep (2015)

Bottom Line: Magnetic materials have found wide application ranging from electronics and memories to medicine.Not only can we tune its transition temperature in a wide range of temperatures around room temperature, but the magnetization can also be tuned from zero to 0.011 A m(2)/kg through an initialization process with two readily accessible knobs (magnetic field and electric current), after which the system retains its magnetic properties semi-permanently until the next initialization process.We construct a theoretical model to illustrate that this tunability originates from an indirect exchange interaction mediated by spin-imbalanced electrons inside the nanocomposite.

View Article: PubMed Central - PubMed

Affiliation: 1] NUS Graduate School of Integrative Sciences and Engineering, National University of Singapore,28 Medical Drive, Singapore 117456 [2] Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 6 Science Drive 2, Singapore 117546 [3] Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117542.

ABSTRACT
Magnetic materials have found wide application ranging from electronics and memories to medicine. Essential to these advances is the control of the magnetic order. To date, most room-temperature applications have a fixed magnetic moment whose orientation is manipulated for functionality. Here we demonstrate an iron-oxide and graphene oxide nanocomposite based device that acts as a tunable ferromagnet at room temperature. Not only can we tune its transition temperature in a wide range of temperatures around room temperature, but the magnetization can also be tuned from zero to 0.011 A m(2)/kg through an initialization process with two readily accessible knobs (magnetic field and electric current), after which the system retains its magnetic properties semi-permanently until the next initialization process. We construct a theoretical model to illustrate that this tunability originates from an indirect exchange interaction mediated by spin-imbalanced electrons inside the nanocomposite.

No MeSH data available.


Schematic of the device geometry and nanocomposite composition.The gray box represents the nanocomposite, with the blue spheres representing the iron-oxide nanoparticles and the brown strips representing the highly defective graphene oxide layers. The nanocomposite’s thin film is deposited on top of a silicon dioxide substrate (in light blue). Two cobalt ferromagnetic electrodes (yellow) are placed on top of the nanocomposite. For zero applied magnetic field, these are pinned in an anti-parallel configuration by PtMn layers (in red).
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f1: Schematic of the device geometry and nanocomposite composition.The gray box represents the nanocomposite, with the blue spheres representing the iron-oxide nanoparticles and the brown strips representing the highly defective graphene oxide layers. The nanocomposite’s thin film is deposited on top of a silicon dioxide substrate (in light blue). Two cobalt ferromagnetic electrodes (yellow) are placed on top of the nanocomposite. For zero applied magnetic field, these are pinned in an anti-parallel configuration by PtMn layers (in red).

Mentions: The device consists of a nanocomposite of partially reduced (between 18% and 20%) and highly defective graphene oxide10 mixed up with iron-oxide (FeO/Fe3O4 complex) core shell structure nanoparticles to which one attaches two pinned ferromagnetic cobalt electrodes whose configuration is driven by an external magnetic field (see Fig. 1). The nanoparticles are in a canted ferrimagnetic alpha-phase and carry magnetic moments of approximately 3 to 5 μB (and typical diameter of 6.5–9.5 nm)11. At room-temperature, due to their small dimension, the nanoparticles are in a superparamagnetic state having their magnetic moment thermally flipping between their two easy axis directions. The graphene oxide contains a high concentration of nanovoids, vacancies and adatoms which carry magnetic moments that are the origin of the paramagnetic response observed in the graphene oxide sheets10 without the iron-oxide nanoparticles. The graphene oxide is partially reduced and thus the carbon atoms whose pz-orbitals are not passivated can be regarded as sites where electrons can localize. The hopping electrons moving through the nanocomposite can hop between these sites through variable range hopping—see supplementary information.


Tunable room-temperature ferromagnet using an iron-oxide and graphene oxide nanocomposite.

Lin AL, Rodrigues JN, Su C, Milletari M, Loh KP, Wu T, Chen W, Neto AH, Adam S, Wee AT - Sci Rep (2015)

Schematic of the device geometry and nanocomposite composition.The gray box represents the nanocomposite, with the blue spheres representing the iron-oxide nanoparticles and the brown strips representing the highly defective graphene oxide layers. The nanocomposite’s thin film is deposited on top of a silicon dioxide substrate (in light blue). Two cobalt ferromagnetic electrodes (yellow) are placed on top of the nanocomposite. For zero applied magnetic field, these are pinned in an anti-parallel configuration by PtMn layers (in red).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4477240&req=5

f1: Schematic of the device geometry and nanocomposite composition.The gray box represents the nanocomposite, with the blue spheres representing the iron-oxide nanoparticles and the brown strips representing the highly defective graphene oxide layers. The nanocomposite’s thin film is deposited on top of a silicon dioxide substrate (in light blue). Two cobalt ferromagnetic electrodes (yellow) are placed on top of the nanocomposite. For zero applied magnetic field, these are pinned in an anti-parallel configuration by PtMn layers (in red).
Mentions: The device consists of a nanocomposite of partially reduced (between 18% and 20%) and highly defective graphene oxide10 mixed up with iron-oxide (FeO/Fe3O4 complex) core shell structure nanoparticles to which one attaches two pinned ferromagnetic cobalt electrodes whose configuration is driven by an external magnetic field (see Fig. 1). The nanoparticles are in a canted ferrimagnetic alpha-phase and carry magnetic moments of approximately 3 to 5 μB (and typical diameter of 6.5–9.5 nm)11. At room-temperature, due to their small dimension, the nanoparticles are in a superparamagnetic state having their magnetic moment thermally flipping between their two easy axis directions. The graphene oxide contains a high concentration of nanovoids, vacancies and adatoms which carry magnetic moments that are the origin of the paramagnetic response observed in the graphene oxide sheets10 without the iron-oxide nanoparticles. The graphene oxide is partially reduced and thus the carbon atoms whose pz-orbitals are not passivated can be regarded as sites where electrons can localize. The hopping electrons moving through the nanocomposite can hop between these sites through variable range hopping—see supplementary information.

Bottom Line: Magnetic materials have found wide application ranging from electronics and memories to medicine.Not only can we tune its transition temperature in a wide range of temperatures around room temperature, but the magnetization can also be tuned from zero to 0.011 A m(2)/kg through an initialization process with two readily accessible knobs (magnetic field and electric current), after which the system retains its magnetic properties semi-permanently until the next initialization process.We construct a theoretical model to illustrate that this tunability originates from an indirect exchange interaction mediated by spin-imbalanced electrons inside the nanocomposite.

View Article: PubMed Central - PubMed

Affiliation: 1] NUS Graduate School of Integrative Sciences and Engineering, National University of Singapore,28 Medical Drive, Singapore 117456 [2] Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, 6 Science Drive 2, Singapore 117546 [3] Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117542.

ABSTRACT
Magnetic materials have found wide application ranging from electronics and memories to medicine. Essential to these advances is the control of the magnetic order. To date, most room-temperature applications have a fixed magnetic moment whose orientation is manipulated for functionality. Here we demonstrate an iron-oxide and graphene oxide nanocomposite based device that acts as a tunable ferromagnet at room temperature. Not only can we tune its transition temperature in a wide range of temperatures around room temperature, but the magnetization can also be tuned from zero to 0.011 A m(2)/kg through an initialization process with two readily accessible knobs (magnetic field and electric current), after which the system retains its magnetic properties semi-permanently until the next initialization process. We construct a theoretical model to illustrate that this tunability originates from an indirect exchange interaction mediated by spin-imbalanced electrons inside the nanocomposite.

No MeSH data available.