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TiO2

-

: Co

7

: ,

100% , .

..
. ..


· · · · · · · ·

(

)

"I swear to tell the truth, all the truth and nothing but the truth"


Novel, multifunctional and smart magnetic materials Heusler alloys Multiferroics Magnetic fluids and composites Magnetic polymers Metamaterials Superconductive materials Diluted magnetic semiconductors and oxides


= half-metallicity

P=(2-1)/3=0.33=33%

P=0

P=1=100%

:


Introduction Low Temperature

Cd1- MnxSe, Hg1-xMnxTe before1987 AIIBVI:Mn GaAs:Mn (Tc=173 K) Si:Mn (>400K) 2004

Furdyna DMS Room Temperature Zavadskii Nagaev Ohno TiO2-:Co (600-800 K) 2001 DMO Dietl ZnO:TM, SnO2:TM, CeO2:TM etc, TM=Mn, Co, Fe Matsumoto Coey Si , HfO2 2004 d0 magnetism=quasiferromagnetism TiO , ZnO, In O Dubroca 2 23 Kaminski& Nanoparticles CeO2, Al2O3, ZnO, Sarma FM in nanostructures 2006 In O , and SnO .
2 3 2

,

There is an ongoing quest for ferromagnetic semiconductors with a Curie temperature well above room temperature, which could be used for a second generation of spin electronics, as well as a search for transparent ferromagnets which can add an optoelectronic dimension.


=Intrinsic Ferromagnetism

Questions: 1. Intrinsic or Extrinsic? (parasitic phases and ferromagnetic clusters) 2. Which ions bear magnetic moment? 3. Type of exchange? (carrier-mediated, superexchange, percolation etc) 4. Does a TM doping play key role?

Si:Mn and TiO2-:Co


Dilute Magnetic Oxides TiO2- : Co Ti
100-x

CoxO2

-

X=0.1-8.0 %

D= 0.2-0.6 µm
Tsubstrate=5500 V= 0.05-0.09 nm/sec

Substrate SrTiO3(100) LaAlO3 (0 01)

Magnetron sputtering

XPS, XAS, XPS, SQUID, VSM, TKE, TEM, AFM Rutile, anatase, TiO Ar O2 Ti+Co O2 SrTiO3(100) O2 O2 Annealing, Rapid Quenching

argon­oxygen atmosphere at oxygen partial pressureo 2x10-6­2x10-4 Torr.


Ti

100-x

O2-:Co

x


Carrier-mediated FM (RKKY type) +percolation


AF superexchange

Fe

3+

­vacancy ­Fe

3+

=F-center=magnetic polaron Coey, 2004


Sarma&Calderon, 2006


Ferromagnetism in Si: Prehistory Si implanted by Ar and Ne ­ low temperature FM (Khoklov&Pavlov 1976) Si implanted with Si, Ar and irradiated by neutrons (Dubroca et al 2006) Si implanted by Xe and Kr (Adashkevich 2007) Si-implanted by Mn (Bolduc 2005, Yoon 2006, MSU-Giredmet ­ 2005-2006, Bandaru 2006. Khaibibulin 2007 ) Si-Mn (evaporation) Kim et al 2003 Tc=210 K Si-Mn (crystalline) Zhang et al 2004 Tc=400 K Si:Mn (sputtering) Demidov et al 2006 Tc>400 K


Above room temperature ferromagnetism in Si:Mn
Si wafers n-type and p-type (D=0.044 cm) -3. 9*10 14 - 2*10 19
55Mn+

implantation 1.10

15

- 5.10

16

­2

Extrion 1000

annealing at 850

0

during 5 min

3 ,0

6

2 ,5

a)

5

b)

N , 1 0 cm

1 ,5

N , 1 0 cm

2 ,0

4

3

1 ,0

2

SIMS, SRP, TEM, XRD, XAS, EXAFS, VSM 300 K, SQUID 4.2-400 K, MO Faraday and Kerr XMCD

-1

20

0 ,5

20

-1

1

0 ,0 0 ,0 0 ,2 0 ,4 0 ,6 0 ,8 1 ,0

0 0 ,0 0,2 0 ,4 0 ,6 0 ,8 1 ,0

h , µm

h , µm



30
K, cm

Faraday Effect in Si:Mn

-1

15

600

0
1
350

5
, µm

10

15

400 F, grad/cm
2

300

250

3

F, grad/cm

200

200

150

0

100

1

2

3
, µm

4

5

6
50

H=8 kOe
~1.65 µm

Si:Mn

0 50

100

150

200

250

300

350

We are unable to explain some observed features

T, K


(

)­

. M 1949 ), 90(Warburg ) 1881 . (

1976 1991 1997 Ames Lab

30

.

2002 G-8 (20%)


15% . Consumption related to temperature control alone (space heating, cooling, and refrigeration) accounts for 50% of the energy consumption in homes (2005 data) and 57% in commercial buildings (2003 data). Consequently, increasing the energy efficiency of refrigeration systems would have a noticeable effect on energy bills.Magnetic refrigeration is a good candidate for making this improvement, as it is more energetically efficient than the process based on the compression/expansion of gases (magnetic refrigerator prototypes can achieve 60% of ideal (Carnot) efficiency, whereas the best commercial conventional refrigerator units can reach only 40%). Moreover, as no refrigerant gases are required for magnetic refrigeration, there is no concern about ozone depletion or greenhouse effect, which contributes further to its environmental


Magnetocaloric effect

15%



Saving 30% of energy Ecologically-friendly Gd is the best material

We are working to find novel materials



· · · · · · · ·

10 (20-40 )


(Q = 0), dS = Q/T = 0.

S S=S(T, , ) :

:

(


SM(T , H) Tad(T , H)

H

= S(T,H)T = T (S,H)

,H=Hf

- S(T,H)T

,H=Hi

, .

H

S,H=Hf

- T (S,H)S

,H=Hi

H

f

S

M

(

T , H

)

H

=µ
H
f

0


H
i

M dH T H

T

ad

(

T , H

)

H

= -µ

0


H
i

T M â dH C (T , H ) T H

RC(H )= S

M (T , H )d

T


Liu et al. Nature, june 2012


X2YZ- full-Heusler alloys XYZ - half-Heusler alloys

F. Heusler 1898 Cu2MnSb 1903

Quaternary XYZ+M Ni-Mn-In-Z

Groot et al (1983) half-metallicity in NiMnSb. Giant MOKE - PdMnSb Reis's group and Miyazaki's group (2006) Co2MnSi Martensitic transition:
Magnetic Shape Memory (MSM) ­ Ni2MnGa (up to 9% ), Direct and Inverse Magnetocaloric Effect, Exchange Bias, Metamagnetism, Kinetic arrest etc



Transition temperatures

Adolf Karl Gottfried Martens (1850-1914)

Sir William Chandler Roberts-Austen (1843­1902)

Courtesy of M.Acet


A scanning Hall probe imaging study of the field induced martensite­austenite phase transition in Ni50Mn34In16 alloy/ V. K. Sharma, J. D. Moore, M. K. Chattopadhyay et al // J. Phys.: Condens. Matter. 2010. V. 22. P. 016008-8


(a)
15
M (emu/g)

Ni48Co2Mn35In15
20 FC, H=5T 0 -20 -0,1 0,0 0,1

TC TM

10

FC

H (T)

5

H=0.01 T ZFC

TCM
=4.2 µ B/f.u.

100

(b)
80 60 40 20 0 0 100 Ni48Co2Mn35In15 ZFC, Ni50Mn35In15 FCC, Ni50Mn35In15 Ni50Mn35In14Al Ni50Mn35In14Ge

Jmax=3 µ B/f.u.

TC

Prior the measurements, the samples were heated up to 400K. The measurements have been generally carried out during heating after the samples were cooled from 400 K to the starting temperature at zero magnetic field that corresponds to the zero field cooled (ZFC) measurements. Some of magnetization data were collected after samples being cooled in a field (FC) and during field cooling cycle (FCC).

M (emu/g)

TM

J

max

T=5K, H=5T

200

300

400

T (K)


2 1

N i 5 0M n 35 I n 6 1 1 1 k 0 4 8

15

T [K]

Oe kO e kO e kO e

0 -1 -2

dM/dT [ emu/( g )]

1

0

-1

Direct measurements of the adiabatic change of temperature, TAD, under an applied magnetic field have been done using adiabatic magnetocalorimeter (MagEq MMS 801 set up) in a temperature range of 250-350 K, and in magnetic fields up to 1.8 T. The external magnetic fields have been ramped at a rate of up to 2T/sec during TAD measurements. The magnetic entropy changes (SM) were estimated from M(H,T) curves using a procedure derived from the Maxwell relation
3 00 3 20 340

-2 2 80

T [K ]


1.0 0.5

Ni50Mn35In14Z

(a)

TAD (K)

H=1T
Z=In Z=Al Z=Ge
290 300 310 320 330 340

g µB J H SM -1.07qR kTC
CP S = T T
ad

2/ 3

0.0 -0.5 -1.0 280

T (K)
2.0 1.5 1.0
Z=In, 321K Z=Al, 324.5K Z=Ge, 310K

Ni50Mn35In14Z SOT H=5T

TAD (K)

0.5 0.0 -0.5 -1.0 -1.5 -2.0 0.5 1.0 FOT

(b)
Z=Ge, 309K Z=Al, 303.5K Z=In, 297.5K

1.5
2/3

H

2/3

(T)

H=1.8 T


= -- , . = 20 -

Ni-Ti, Pt-Ti, Pt-Ga, Pt-Al c : , , .


-- , .




, ­ .

,

,

­ =c


"

-- -- !"

, , :

. . ...