magnetism: some issues and understandingssol.postech.ac.kr/~bimin/spin-min/muju02-2.pdf ·...
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Magnetism:some issues and understandings
B. I. MinDept. Physics & eSSC, POSTECH
Thanks to MTG members
Magnetism Theory Group / POSTECH
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1. Prof. Duk Joo Kim
2. Phonon effects on magnetism
3. Ubiquitous half-metallic systems
4. Concluding remarks
Magnetism Theory Group / POSTECH
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Magnetism Theory Group POSTECH
B.S. Mathematics (1956), University of Tokyo
B.S. Physics (1958), University of Tokyo
Ph.D. Physics (1963), University of Tokyo
Thesis: "Localized state in dilute alloy" (advisor: Prof. R. Kubo)
-----------------------------------
Post Doc (1963-1965), University of Tokyo
Lecturer (1965-1965), University of Tokyo
Research Staff (1965-1971), National Magnet Lab, MIT
Professor (1971-1997), Aoyama Gakuin University
Prof. Duk Joo Kim (1934-1997)
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Magnetism Theory Group POSTECH
Keywords:
• Itinerant electron magnetism • Exchange interaction• Electron--phonon interaction • Electron gas: jellium model • Magnetism phonon • INVAR
•금속전자계의 다체이론: 자성과 격자진동 (1986)(Many body theory of electrons in metals: magnetism and phonons)
•The electron-phonon interaction and itinerant electron magnetism", Physics Reports, 171, 129 (1988)
•New Perspectives in Magnetism of Metals (1999)
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Magnetism Theory Group POSTECH
Spin excitations in itinerant electron model
Izuyama, Kim, Kubo, JPSJ (1963)
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Magnetism Theory Group POSTECH
Phonon effects on magnetism
Ee(M)/N
kΤc
kΘDEph(M)/N
M
Ee(M) >> Eph(M) kΤc ~ kΘD
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Magnetism Theory Group POSTECH
Phonon contribution to the Stoner susceptibility
V: exchange interactionJph: phonon exchange
D.J.Kim (1982)J.D. Lee (1995)
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Magnetism Theory Group POSTECH
Hidden excitation
Ishikawa, J MAGN MAGN MATER (1979) D.J. Kim, J MAGN MAGN MATER (1997)
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Magnetism Theory Group POSTECH
Isotope effect in itinerant systems
susceptibility
i
i
M ddMχ
χ
( )V ε
/Wε
D. J. KimK. Kim/Wε
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Magnetism Theory Group POSTECH
Isotope effect in CMR systems
LaCaMnO3 (x=0.2) LaCaMnO3 (x=0.5)
Zhao, Nature (1996) Zhao, PRB (1999)
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Magnetism Theory Group POSTECH
INVAR: FeNi
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Magnetism Theory Group POSTECH
β: thermal expansion, γ: Grueneisen constant
D.J. Kim, PRB (1989)
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Magnetism Theory Group POSTECH
f.c.c. FeNi alloy at four different volumes(32 atoms supercell with 21 Fe and 11 Ni)
Ni0.34Fe0.66van Schilfgaarde, Nature (1999)
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Magnetism Theory Group POSTECH
Magnon softening and damping
Dai et al. PRB (2000)
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Half-Metals: 100% spin-polarized conduction carriers
Density of states (DOS)
Si (insulator)
CrO2 (half-metal)
(Tc=390K)Fe (metal)
Pickett, Physics Today (2001)
Magnetism Theory Group / POSTECH
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Magnetism Theory Group POSTECH
Spin transport / injection
Prinz, Science (1998 ) Ohno, Nature (1999)
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Half-Metallic band structure for Heusler NiMnSb
Tc = 728K
R. A. de Groot, PRL (1983)
Magnetism Theory Group / POSTECH
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Magnetism Theory Group POSTECH
CMR perovskite LaAMnO3
A=CaPickett+Singh, PRB (1996) Tc ~ 300K
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Experiments on Half-Metals
Supercurrent conversion at the
superconductor-metal(A,B), -HM(C,D)
interface
PES from the surface of a
thin film of La0.7Sr0.3MnO3
J.H. Park, Nature (1998) Soulen, Science (1998)
Magnetism Theory Group / POSTECH
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Magnetism Theory Group POSTECH
Double perovskite Sr2FeMoO6
Kobayashi, Nature (1998) Tc ~ 450K
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Magnetism Theory Group POSTECH
Ga(Mn)As
Tc = 110K
Ohno, JMMM (1999)
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Magnetism Theory Group POSTECH
LSDA TiO2+Co
M.S.Park (2002)J.H.Park (2000)
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HM-AFM double perovskites
W. E. Pickett, PRB (1998)
Magnetism Theory Group / POSTECH
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Concluding remarks
Role of phonons in magnetism
itinerant systems, Invar
CMR perovskites
Spintronic devices @room T:
Half-metals,
diluted Magnetic semiconductors
New spintronic materials
Magnetic mechanisms
21C: Renaissance in magnetism
Magnetism Theory Group / POSTECH