Magnetic Layer-by-Layer Architecture Using Inorganic Nanosheets

Takashi Yamamoto (Keio University)

Molecule based magnets are still a relatively new class of materials, fascinating because of the potential applications in information storage, displays, electronic and spintronic devices. However, such applications will require putting the active materials on a surface or interfacing with other components. In the present study, we focus on fabricating multi-functional magnetic ultrathin films using inorganic nanosheets as a building block.

1. Photomagnetic films of Prussian Blue and titania nanosheets1) The ultrathin films were prepared by the modified Langmuir-Blodgett method using a titania suspension and tetrabutylammonium cations as the subphase and the confinement agent, respectively. Prussian Blue was deposited onto the titania films by a sequential adsorption technique. Upon band gap excitation of titania nanosheets, electron injection into Prussian Blue was achieved with scavenging interlayer water molecules, resulting in photoreduction to Prussian White. This phenomenon is due to the larger band gap energy of titania nanosheets, which, in turn, possesses a strong oxidation power of generated holes. Since the process proceeds at the interface between the materials, reducing the dimensionality of a magnetic material is an effective approach to observe such a photomagnetic effect.

2. Anisotropically integrated magnetic films of layered double hydroxides nanosheets The ultrathin films were prepared by the electrostatic layer-by-layer technique using a suspension of a magnetic layered double hydroxide (LDH) suspension and a smectite clay. In the magnetic measurement of the [Co-Ni LDH / SSA] film at 2 K, the magnetization depended on the film orientation with respect to the applied field. The magnetization of the perpendicular orientation (H⊥) to the applied field is stronger than that of parallel orientation (H//). The coercive field is 280 and 150 Oe for the H⊥ and H//, respectively. It is indicated that the [Co-Ni LDH / SSA] film exhibits a perpendicular magnetic anisotropy due to a uniaxial integration of Co-Ni LDH nanosheets. Incorporation of photoactive inorganic nanosheets enables the design of a photoresponsive spintronics devices.

[1]Yamamoto, T.; Saso, N.; Umemura, Y.; Einaga, Y. J. Am. Chem. Soc. 2009, 129, 13196

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