Magnetism:some issues and understandings

B. I. MinDept. Physics & eSSC, POSTECH

Thanks to MTG members

Magnetism Theory Group / POSTECH

1. Prof. Duk Joo Kim

2. Phonon effects on magnetism

3. Ubiquitous half-metallic systems

4. Concluding remarks

Magnetism Theory Group / POSTECH

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)

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)

Magnetism Theory Group POSTECH

Spin excitations in itinerant electron model

Izuyama, Kim, Kubo, JPSJ (1963)

Magnetism Theory Group POSTECH

Phonon effects on magnetism

Ee(M)/N

kΤc

kΘDEph(M)/N

M

Ee(M) >> Eph(M) kΤc ~ kΘD

Magnetism Theory Group POSTECH

Phonon contribution to the Stoner susceptibility

V: exchange interactionJph: phonon exchange

D.J.Kim (1982)J.D. Lee (1995)

Magnetism Theory Group POSTECH

Hidden excitation

Ishikawa, J MAGN MAGN MATER (1979) D.J. Kim, J MAGN MAGN MATER (1997)

Magnetism Theory Group POSTECH

Isotope effect in itinerant systems

susceptibility

i

i

M ddMχ

χ

( )V ε

/Wε

D. J. KimK. Kim/Wε

Magnetism Theory Group POSTECH

Isotope effect in CMR systems

LaCaMnO3 (x=0.2) LaCaMnO3 (x=0.5)

Zhao, Nature (1996) Zhao, PRB (1999)

Magnetism Theory Group POSTECH

INVAR: FeNi

Magnetism Theory Group POSTECH

β: thermal expansion, γ: Grueneisen constant

D.J. Kim, PRB (1989)

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)

Magnetism Theory Group POSTECH

Magnon softening and damping

Dai et al. PRB (2000)

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

Magnetism Theory Group POSTECH

Spin transport / injection

Prinz, Science (1998 ) Ohno, Nature (1999)

Half-Metallic band structure for Heusler NiMnSb

Tc = 728K

R. A. de Groot, PRL (1983)

Magnetism Theory Group / POSTECH

Magnetism Theory Group POSTECH

CMR perovskite LaAMnO3

A=CaPickett+Singh, PRB (1996) Tc ~ 300K

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

Magnetism Theory Group POSTECH

Double perovskite Sr2FeMoO6

Kobayashi, Nature (1998) Tc ~ 450K

Magnetism Theory Group POSTECH

Ga(Mn)As

Tc = 110K

Ohno, JMMM (1999)

Magnetism Theory Group POSTECH

LSDA TiO2+Co

M.S.Park (2002)J.H.Park (2000)

HM-AFM double perovskites

W. E. Pickett, PRB (1998)

Magnetism Theory Group / POSTECH

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