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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.


Magnetization and capacitance for different initialization processes.(a) Magnetization as a function of temperature for samples initialized with different Bext. The transition temperature can be made to vary from 276 K (Bext = 0.02 T) to 317 K (Bext = 0.04 T). (b) Capacitance measurement for several different Bext corresponding to distinct electrodes configuration (see text and Fig. 1 for details).
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f2: Magnetization and capacitance for different initialization processes.(a) Magnetization as a function of temperature for samples initialized with different Bext. The transition temperature can be made to vary from 276 K (Bext = 0.02 T) to 317 K (Bext = 0.04 T). (b) Capacitance measurement for several different Bext corresponding to distinct electrodes configuration (see text and Fig. 1 for details).

Mentions: If no electric current is passed across the device, the nanocomposite is paramagnetic for all tested temperatures. This indicates that the nanocomposite’s magnetic moments (both from the iron oxide nanoparticles and from the defective graphene oxide) are essentially independent. The nanocomposite remains paramagnetic when a spin-unpolarized electric current is passed across it. However, using ferromagnetic electrodes to inject a spin-polarized current into the nanocomposite, the system can be made to undergo a ferromagnetic transition depending on the particular magnetic configuration of the electrodes. Of practical interest is the fact that this configuration can be controlled by an external magnetic field. Has shown in Fig. 2, the initialization is done with two accessible knobs: a potential bias driving an electric current that is injected into the nanocomposite through two ferromagnetic electrodes; and an external magnetic field (with a magnitude of the order of tens of mT) driving the magnetic configuration of the electrodes. These two knobs determine the device’s magnetic properties which remain stable for as long as we have measured it (several weeks) after the electric current and magnetic field are turned off.


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)

Magnetization and capacitance for different initialization processes.(a) Magnetization as a function of temperature for samples initialized with different Bext. The transition temperature can be made to vary from 276 K (Bext = 0.02 T) to 317 K (Bext = 0.04 T). (b) Capacitance measurement for several different Bext corresponding to distinct electrodes configuration (see text and Fig. 1 for details).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Magnetization and capacitance for different initialization processes.(a) Magnetization as a function of temperature for samples initialized with different Bext. The transition temperature can be made to vary from 276 K (Bext = 0.02 T) to 317 K (Bext = 0.04 T). (b) Capacitance measurement for several different Bext corresponding to distinct electrodes configuration (see text and Fig. 1 for details).
Mentions: If no electric current is passed across the device, the nanocomposite is paramagnetic for all tested temperatures. This indicates that the nanocomposite’s magnetic moments (both from the iron oxide nanoparticles and from the defective graphene oxide) are essentially independent. The nanocomposite remains paramagnetic when a spin-unpolarized electric current is passed across it. However, using ferromagnetic electrodes to inject a spin-polarized current into the nanocomposite, the system can be made to undergo a ferromagnetic transition depending on the particular magnetic configuration of the electrodes. Of practical interest is the fact that this configuration can be controlled by an external magnetic field. Has shown in Fig. 2, the initialization is done with two accessible knobs: a potential bias driving an electric current that is injected into the nanocomposite through two ferromagnetic electrodes; and an external magnetic field (with a magnitude of the order of tens of mT) driving the magnetic configuration of the electrodes. These two knobs determine the device’s magnetic properties which remain stable for as long as we have measured it (several weeks) after the electric current and magnetic field are turned off.

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.