PHYSICS/BK21 SEMINAR (08/05/14)
관련링크
본문
"Seeing and manipulating spin-spin interactions at the single atomic level
연사: Dr. Donghun Lee[Ohio State University]
일시: 2008 년 5 월 14 일 15:00~16:00
장소: 물리학과 세미나실(3-201호)
ABSTRACT:
The 2007 Nobel prize in physics went to Albert Fert and Peter Gr?berg 밼or the discovery of Giant Magnetoresistance (GMR)?which is an effect that underlies all of the read sensors in today뭩 hard disk drives. These initial studies of GMR have opened a new paradigm for future electronics called몊pintronics? In contrast to conventional charge-based electronics, spintronics relies on the electron뭩 spin, which is a fundamental magnetic moment that has two energy states, spin-up or spin-down, analogous to the 1 or 0 states of a bit in a computer. One key challenge for the realization of spintronics is the development of ferromagneticsemiconductors which could potentially combine magnetic recording and digital logic in asingle device. One promising candidate is GaMnAs, in which nonmagnetic GaAs can be made ferromagnetic by introducing only a few percent of Mn. The low ferromagnetic transition temperature (currently Tc<170K) of GaMnAs, prevents use in practical devices which operate at room temperature. A betterunderstanding of GaMnAs at a micros copic level is necessary to probe the limits of Tc in this material. We have built a low temperature (<12.5K) ultrahigh vacuum (<1?0-10 Torr) scanning tunnelingmicroscope (STM) to study spin-spin interactions in GaMnAs at the atomic level. Our STM can be used to image semiconductor surfaces with atomic resolution, manipulate individual Mn atoms, and spectroscopically probe Mn-Mn interactions. A clean GaAs surface is prepared by cleaving a p-type GaAs crystal inside the ultrahigh vacuum chamber. A low coverage of Mn atoms is thenevaporated onto the surface. To more closely mimic a bulk-like environment, single Mn atoms can be substituted for Ga in the first layer of the surface, by applying a voltage pulse with the STM tip. To study Mn-Mn interactions, we make pairs of substituted Mn. Our STM studies on Mn pairsshow interesting spin-spin interactions which strongly depend on the Mn separation and relativecrystal orientation. For example, coupling between two Mn atoms switches from ferromagnetic (parallel spins) to antiferromagnetic (antiparallel spins) depending on the pair뭩 orientation. We are also developing a capability for spin-polarized STM to better study long range magnetic ordering between pairs and larger clusters of substituted Mn.By using a magnetic STM tip such as Ni or Cr, spin-polarized STM can selectively detect different spin states of Mn clusters
문의처: 정윤희(054-279-2078, yhj@postech.ac.kr)
"
연사: Dr. Donghun Lee[Ohio State University]
일시: 2008 년 5 월 14 일 15:00~16:00
장소: 물리학과 세미나실(3-201호)
ABSTRACT:
The 2007 Nobel prize in physics went to Albert Fert and Peter Gr?berg 밼or the discovery of Giant Magnetoresistance (GMR)?which is an effect that underlies all of the read sensors in today뭩 hard disk drives. These initial studies of GMR have opened a new paradigm for future electronics called몊pintronics? In contrast to conventional charge-based electronics, spintronics relies on the electron뭩 spin, which is a fundamental magnetic moment that has two energy states, spin-up or spin-down, analogous to the 1 or 0 states of a bit in a computer. One key challenge for the realization of spintronics is the development of ferromagneticsemiconductors which could potentially combine magnetic recording and digital logic in asingle device. One promising candidate is GaMnAs, in which nonmagnetic GaAs can be made ferromagnetic by introducing only a few percent of Mn. The low ferromagnetic transition temperature (currently Tc<170K) of GaMnAs, prevents use in practical devices which operate at room temperature. A betterunderstanding of GaMnAs at a micros copic level is necessary to probe the limits of Tc in this material. We have built a low temperature (<12.5K) ultrahigh vacuum (<1?0-10 Torr) scanning tunnelingmicroscope (STM) to study spin-spin interactions in GaMnAs at the atomic level. Our STM can be used to image semiconductor surfaces with atomic resolution, manipulate individual Mn atoms, and spectroscopically probe Mn-Mn interactions. A clean GaAs surface is prepared by cleaving a p-type GaAs crystal inside the ultrahigh vacuum chamber. A low coverage of Mn atoms is thenevaporated onto the surface. To more closely mimic a bulk-like environment, single Mn atoms can be substituted for Ga in the first layer of the surface, by applying a voltage pulse with the STM tip. To study Mn-Mn interactions, we make pairs of substituted Mn. Our STM studies on Mn pairsshow interesting spin-spin interactions which strongly depend on the Mn separation and relativecrystal orientation. For example, coupling between two Mn atoms switches from ferromagnetic (parallel spins) to antiferromagnetic (antiparallel spins) depending on the pair뭩 orientation. We are also developing a capability for spin-polarized STM to better study long range magnetic ordering between pairs and larger clusters of substituted Mn.By using a magnetic STM tip such as Ni or Cr, spin-polarized STM can selectively detect different spin states of Mn clusters
문의처: 정윤희(054-279-2078, yhj@postech.ac.kr)
"
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