PHYSICS/BK21 SEMINAR[5.20]

    “Dynamic nanomechanical probing of material properties:

         from elastic moduli to spin-orbit coupling”

 * Speaker : Dr. Yun Daniel Park (Seoul National University)

 * Place : Physics Seminar Room (Science Bldg, 3-201)

 * Date & Time : May  20 (Thu.)  4:00  ~  5:00 pm

Ø Abstract

The seminar is in two parts, with an overall theme to utilize nanomechanical

structures to study material physics, from elastic theory to carrier-mediated

ferromagnetic ordering, at nanoscales. The first is to outline a need for material

characterization at the ‘chip-level’: scaling material property measurement techniques

at nanoscales. Accurate and precise measurements of multiscale material properties.

such as elastic moduli and thermal conductivities. become nontrivial at nanoscales.

Characterization techniques need to minimize the effects of an experimental set-up,

requiring micromachining and integration of experimental probes. Elastic moduli can

be measured from dynamic flexural response of freestanding nanostructures. Thermal

conductivities can be also measured from freestanding nanostructures, isolated from

environmental effects, with integrated temperature sensors and heaters. As an

example, enhancements in thermal-elastic properties of a nanolaminate composed of

metallic thin-film (Al) and self-assembled carbon nanotubes (Al-CNT) is

demonstrated [1]. The second part is to demonstrate the ability to selectively

manipulate material properties at nanoscales by utilizing integrated nanomechanical

probes. Recently, there has been a wide-ranging interest in the effects of strain: from

commercially driven strained-Si with its high mobilities to fundamentally interesting

graphene and multiferroic perovskite transition metal oxides. Here, I will demonstrate

the effect of local strain at nanoscales on the intrinsic Anomalous Hall Effect (AHE)

of a diluted magnetic semiconductor GaMnAs [2]. By realizing a mechanically-

buckled Hall microbar with multiple probes, we can deduce the effects of strain on

both the ferromagnetic ordering and magnetic anisotropy. We find large reduction in

both the AHE and planar Hall Effect with compressive stress. From such findings,

we demonstrate a simple and scalable mechanical low-power memory element with

large signal-to-noise ratios.

 [1] J. H. Bak, et al., Nature Mater. 7, 459 (2008).

[2] S. H. Chun, et al., Phys. Rev. Lett. 98, 026601 (2007).

Contact Person : Prof. Jaehoon Park (054-279-2088, jhp@postech.ac.kr)