GROWTH AND INVESTIGATION OF HALF-METALLIC Fe3O4 THIN FILMS B. Vengalis, V. Lisauskas, A. Lisauskas, K. - PowerPoint PPT Presentation

Loading...

PPT – GROWTH AND INVESTIGATION OF HALF-METALLIC Fe3O4 THIN FILMS B. Vengalis, V. Lisauskas, A. Lisauskas, K. PowerPoint presentation | free to download - id: 20fe99-ZDc1Z



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

GROWTH AND INVESTIGATION OF HALF-METALLIC Fe3O4 THIN FILMS B. Vengalis, V. Lisauskas, A. Lisauskas, K.

Description:

Growth of Fe3O4 thin films by magnetron sputtering. Characterization of crystalline structure ... DC Magnetron sputtering. Reflected High Energy Electron ... – PowerPoint PPT presentation

Number of Views:125
Avg rating:3.0/5.0
Slides: 13
Provided by: tcd
Learn more at: http://www.tcd.ie
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: GROWTH AND INVESTIGATION OF HALF-METALLIC Fe3O4 THIN FILMS B. Vengalis, V. Lisauskas, A. Lisauskas, K.


1
GROWTH AND INVESTIGATION OF HALF-METALLIC Fe3O4
THIN FILMSB. Vengalis, V. Lisauskas, A.
Lisauskas, K.Šliužiene, V. Jasutis Semiconductor
Physics Institute, Vilnius LithuaniaM. A. Bari,
J.J. Versluijis, J. M. D. CoeyPhysics
Department, Trinity College, Dublin 2, Ireland
MAGNETIC DEVICES BASED ON THIN FILM
MULTILAYERS 11-12 July 2002, Dublin, Ireland
2
Short outline of this report
  • Magnetite as promising material for
    magnetoelectronics
  • Fe3O4 thin films and related technological
    problems
  • Growth of Fe3O4 thin films by magnetron
    sputtering
  • Characterization of crystalline structure
  • Electrical and magnetic properties
  • Conclusions

3
Magnetite crystalline structure, attractive
properties
Ferrimagnetic ordering at TltTC ? 860 K (M 4
?B ) Charge ordering at TltTV120 K (Verwey
transition)
Crystalline structure Cubic inverse spinel
structure Fd3m O2- ions form frame of face
centered cubic lattice, a 0,8398 nm
Electrical conductivity ?( 300 K)? 10 m?cm due
to hopping of spin-polarized electrons between
magnetically ordered Fe3 ir Fe2 states in B
positions
Ionic model Fe3A Fe3Fe2B O2- Fe3
occupies 1/8 tetrahedral positions (A) Fe3and
the same amount of Fe2 occupy 1/2 possible B
positions
4
Magnetite phase diagram, technology problems
Advantages
Phase diagram of Fe-O
  • High TC value compared to other HM oxides
    La2/3Sr1/3MnO3 , Sr2FeMoO6, CrO2
  • Simple structure, one element
  • Low deposition temperature

Iron Fe (Cubic) Maghemite ? - Fe2O3
(Rhomohedr) Magnetite - Fe3O4 (Cubic) Wuestite
FeO (Rhombohedral)
Problems
  • Presence of isostructural phases in Ph. D.
  • Limited choice of lattice-matched substrate
    materials
  • There is a need in suitable isolating and
    conducting materials for heterostructures
  • Stability of Fe3O4 in various oxygen ambient
    needs to be studied
  • Stability of interfaces needs to be studied

5
Preparation of Fe3O4 thin films by various authors
Technology Target P(O2), Pa Ts, ?C Substrate Film quality References
PLD ?-Fe2O3 ?-Fe2O3 ?-Fe2O3 ?-Fe2O3 ?-Fe2O3 ?-Fe2O3 Fe3O4 3x10-1 lt1x10-1 lt1x10-1 lt1x10-1 lt1x10-1 1x10-3 10-4 350 350 350 350 570 350 350 Si MgO(100) SrTiO3(100) ?-Al2O3 SrTiO3 MgO(100) MgO(100) P E (0.3) E ( 8 ) E E E E JAP 83 (1998) 7049 PR(B)57(1998)7823 PR(B)64(2001)205413
DC-MS Fe 2x10-1 500 MgO(100) MgAl2O4 E E (4 ) PR(B) 53(1996)9175
RF-MS Fe 5x10-1 20, 400 ?-SiO2 P J.A.P.75(1994) 431
RF-MS Fe3O4 10-2 250 MgO E PR(B)80(2002)823
DC-MS Fe 1.5x10-1 350-450 MgO(100) E This work
6
Preparation of Fe3O4 thin films in this work
DC Magnetron sputtering.
Target Fe disk, 35 mm diam
(h0.5 mm) Substrates Cleaved MgO(100)
(aMgO0.42 nm? ½ aFe3O4)
Glass

Temperature Ts 300, 400, 450?C Gas ambient
ArO2 301, (p
? 5 Pa)
Film thickness (d50?600 nm)
Deposition rate versus substrate to target
distance at Idisch 95 mA.
7
Microstucture of the grown Fe3O4 thin films
Regions of deposition rate resulting growth of
single phase, epitaxial (E) and policrystalline
(P) Fe3O4 at p(O2)?0.15 Pa as found from XRD,
RHEED and resistivity measurements
Fe3O4 / MgO
Fe3O4 / MgO
Fe3O4 / Glass
Reflected High Energy Electron Diffraction (RHEED)
8
Fe3O4 thin films on MgO and Glass. Optical
absorption
?, 104 cm-1
Fe3O4
Fe3O4
d, (?) 0.16 0.27 0.42
5.5
MgO
4.5
3.5
TI / Is ?(h?)? - ln T / d
2.5
E, eV
9
Resistance versus temperature of Fe3O4 thin
films grown epitaxially on MgO(100) at 400?C
T gtTV
Activation R(T) behaviour
?(T) ?? exp(-Ea /kT)
T ltTV
Variable range hopping (Motts low)
?(T) A exp(B /T)1/4
10
Resistance versus temperature of Fe3O4/MgO thin
films
1
1
27
4
34
4
1/T
1/T
DR, nm/min
27
DR, d
34
42
Ts450?C
Resistance anomaly at TVv was only seen for
Fe3O4/MgO films grown at 350 and 400 ?C
Activation energy of R(T) behavior at TgtTV for
epitaxial Fe3O4 films depends sensitively on
crystalline quality
11
Stability of Fe3O4 thin film during heating
(dT/dt7deg/min)
  • Fe3O4 thin film is stable during heating in
    vacuum up to 650 ?C.
  • Nonreversible resistance change appears at 200
    and 400?C during heating in oxygen at P(O2)105
    Pa and 0,16 Pa, respectively

12
Conclusions
1. Magnetite is realy an intersting material! 2.
It likes vacuum and doesnt like oxygen 3. High
quality Fe3O4 thin films exhibiting resistance
anomaly in the vicinity of Verway transition
point were grown heteroepitaxially at 350 and
400 ?C on lattice-matched MgO(100) substrates by
a reactive DC magnetron using metallic Fe target.
You can try also. 3. We point out the Fe/O2 ratio
(sputtering rate at a fixed oxygen pressure) of
key importance for growth of single phase films.
About PowerShow.com