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Новые магнитные состояния в кристаллах PowerPoint PPT Presentation


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Новые магнитные состояния в кристаллах. А.И.Смирнов. Институт физических проблем им. П. Л. Капицы РАН. МФТИ 3 марта 2006. Ферромагнетики и антиферромагнетики. 2. Квантово - разупорядоченные основные состояния магнитных кристаллов Квазиодномерные, димерные и фрустрированные магнетики.

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Новые магнитные состояния в кристаллах

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5084448

..

. . .

3 2006


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2. - ,

3.


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=2a(293K)


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MnF2


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H =SJi,i+1 SiS i+1

H = Ji,i+1S[SzjSzj+1+1/2(S+jS-j+1 +S-jS+j+1 )]

S+i= Sxi+iSyi S-i= Sxi-iSyi

J > 0

-

-

c


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T=0

:

E ~ (grad Q)2 ~ k2Q 2 ~ eknk

wk = ak

Q 2 ~ eknk/k2 ~nk/k ~1/k

T=0

nk=1/2

q 2dk ~

dM ~

dk/k

k

k


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S=1/2 ( )

0

-1/4

-ln2+1/4 (H.Bethe, 1931)

<S>=0

z

x

=

-3/4

-E/NJ


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CuCl2 *2N(C5H5)

KCuF3


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( )


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NIST

n2

n1


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(

)

. . 1993


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( )

CuCl2 *2N(C5H5)

Endoh et al PRL1974


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( )

(

)

KCuF3

D. Tennant et al 2000


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S=1/2

--

a

GAPLESS

SPIN-GAP

<Sz>=0

x =

<Sz>=0

x = v/D

8


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-

Hase et al PRL 1993


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S=1

| g.s.> =

i0hihi0hihh0ihih0ihihihih +

<S> = 0

z

x

~ 7

D

=

0.41J

:

H

c

T

J

J


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Structure and susceptibility of a Haldane magnet

(Pb2+)

Uchiyama et al PRL 1999


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  • :

  • - S=1/2

  • -

  • S=1,

  • S=1/2


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E

S=1, Sz=1

S=1, Sz=0

S=0

S=1, Sz=-1

Hc

H

-

?

1:

TlCuCl3

Glazkov et al 2003


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(!!??)

TlCuCl3


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-

?

2: -

Miyashita &Yamamoto

PRB 1993

( )


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)

x

/

r

-

(

p

x

e

~

e

p

o

l

e

v

n

e

s

n

i

p

S

-

-

-

-

-

-

+

+

+

+

+

+

-

-

-

-

-

-

+

+

+

+

+

-

-

-

-

+

+

+

+

+

+

-

-

-

-

-

+

+

+

+

+

+


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(!!!???)

-

l

m

x =

Cu(1-x)MgxGeO3

Uchiyama et al PRL 1999

Masuda et al PRL 1998


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26.3 GHz ESR

CuGeO3+2.88% Mg

-

Glazkov, Smirnov et al PRB 2002


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:

J S2 exp(-2L/x) ~ kBT


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,

Glazkov et al

PRB 2002


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( ) (!!!???)

-

Yasuda et al PRB 2001


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: .


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S1

S2

S3


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,

?

.

Make money


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:

T=0 (!!!???)

T, K


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Macroscopic amount of degenerate states with minimum energy.

J>0

The rotation of spins at eachhexagon

by an arbitrary angle does not break

the condition S=0at each tetrahedron,

with no change of the total energy

Minimum energy atS=0

No order until low temperatures: T<< TCW


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:

, (!!!???)


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H

Test for the degenerate modes by the

Experiment on adiabatic demagnetization

thermometer

sample

charcoal cryopump

with a heater

vacuum/

exchange gas


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:


Quasi adiabatic demagnetization

Quasi-adiabatic demagnetization

H || (111) plane

Overall heat leaks

310-7

Solid lines are

MC-simulations

Sosin et al PRB 2005


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J>0

Minimum energy atS=0

No order until low temperatures: T<< TCW


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Temperature evolution of magnetic resonance lines

Sosin et al unpublished


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J.R. Stewart et al JPCM 2004

Spin structures suggested for the ordered phase of Gd2Ti2O7


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:!!!! ????

T=0.

-

.

.

. .

.

http://www.kapitza.ras.ru/rgroups/esrgroup/Welcome.html

[email protected]

Tel. 1370998


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http://www.kapitza.ras.ru/rgroups/esrgroup/Welcome.html

[email protected]

Tel. 1370998


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