investigation of cobalt ferrite based materials for stress sensor and actuator design introduction...
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Investigation of cobalt ferrite based materials for stress sensor and actuator design
INTRODUCTION
• Stress sensors can be used to monitor the health of buildings and structures
– The change is dimensions of a material due to a change in its magnetisation is called magnetostriction ().
– The inverse magnetostriction effect (Villari effect): magnetisation changes upon changing the dimensions.
– Magnetic stress sensors can be made using magnetostrictive materials. Surface field changes on change in dimensions, which can be used to measure stress.
WHY COBALT FERRITE?
Exhibits magnetostriction sensitivity (d/dH)
Is cheap, and mechanically and chemically robust
SENSITIVITY AND RANGE
N. Ranvah, I.C. Nlebedim, Y. Melikhov, J. E. Snyder, P. I. Williams, A. J. Moses and D. C. Jiles
Wolfson Centre for Magnetics, School of Engineering, Cardiff University, The Parade, Cardiff – CF24 4QU
Magnetoelastic properties of cobalt ferrite can be improved by chemical substitution
CURRENT STUDY
RESULTS
Effect of non-magnetic Ge4+ ion substitution
Lower anisotropy
Lower anisotropy leads to
Higher sensitivity
Ge4+ goes into A-sites and more Co2+ into B-sites Higher range
CONCLUSIONS
SELECTED REFERENCES Chikazumi, S. (1997), Physics of Ferromagnetism, Oxford University Press, Great
Clarendon Street, Oxford, OX2 6DP. Lee, S. J.; Lo, C. C. H.; Matlage, P. N.; Song, S. H.; Melikhov, Y.; Snyder, J. E. &
Jiles, D. C. (2007), 'Magnetic and magnetoelastic properties of Cr-substituted cobalt ferrite', Journal of Applied Physics 102(7), 073910.
Melikhov, Y.; Snyder, J. E.; Jiles, D. C.; Ring, A. P.; Paulsen, J. A.; Lo, C. C. H. & Dennis, K. W. (2006), 'Temperature dependence of magnetic anisotropy in Mn-substituted cobalt ferrite', JOURNAL OF APPLIED PHYSICS 99, 08R102.
Song, S. .H. (2007), 'Magnetic and magnetoelastic properties of M-substituted cobalt ferrites (M=Mn, Cr, Ga, Ge)', PhD thesis, Iowa State University, Ames, Iowa.
RESULTS
ACKNOWLEDGEMENTS
This research was supported by the UK Engineering and Physical Sciences Research Council under grant number EP/D057094 and by the US National Science Foundation under grant number DMR-0402716.
Power consumption
A Co1.1Ge0.1Fe1.8O4 based device will need 93.75% less power if operated at
the same range as pure cobalt ferrite.
Email: [email protected]
Material
Magnetostrictivematerial
Sensor Electronics
Material
Magnetostrictivematerial
Sensor Electronics
,11
2,max ,2
mag
mag
IH
H I
2
1
is the magnetostriction
1
2
H1 H1,max H2,max
1
2
CoFe2O4
Ge4+/Co2+
Substitution Co1+xGexFe2-2xO4
CUBIC SPINEL LATTICE
TetrahedralOctahedral
B A
The two sites on cobalt ferrite lattice:
Fe3+ Fe3+
Co2+ Properties depend on site preference of substituted ions
Complete inverse spinel: [Fe]A[CoFe]BO4
Cobalt ferrite is reported to have some Co in A-sites as well
SITE OCCUPANCY OF IONS
• Co2+ in B-sites Higher magnetostriction Higher Anisotropy Lower sensitivity
• Non-magnetic ion substitution Lower Anisotropy
•
•
Mn3+
Cr3+B-sites (Octahedral)
Ga3+
Ge4+A-sites (Tetrahedral)
SITE OCCUPANCY OF IONS
•Higher Moment Higher Magnetostriction (higher range of operation)
•Internal coupling reduces Anisotropy reduces (higher sensitivity)
Co2+ Fe3+ Ge4+
++
B-site A-site B-site
Beforesubstitutio
n=
Net Moment
Substitution
IN IN OUTOUT
B-site A-site B-site
+ +Aftersubstitutio
n
=
Net Moment
,11
2 ,2
25%mag
mag
IH
H I
1
2
6.25%P
P
Energy Saved 93.75%
More Cobalt in B-sites
Co2+/Ge4+ substitution
LowerExchangecoupling
Lower Anisotropy
Higher Sensitivity (d/dH)
Higher Magnetostriction()
Higher range of operation, lower power consumption, less hysteresis
Candidate for sensor or actuator applications