÷zden ÷zdemir

        Ph.D., Newcastle upon Tyne

        Senior Research Associate

Fine particle magnetism of ferrimagnetic and antiferromagnetic iron oxides: magnetic

domain structures; effect of chemical changes on magnetization; low-temperature phase transition.




Research Interests

My main interests are in fundamental rock magnetism. My research is mostly directed towards understanding how the ferrimagnetic minerals in rocks lead to magnetic memory in the form of thermal and chemical remanent magnetization. Such magnetizations are phenomenally stable and provide a record of the history of the Earth 's crust and the geomagnetic field.

One of my major interests is in magnetic effects associated with chemical changes. Many naturally occurring oxidation, reduction and alteration processes transform the crystal structure of the ferrimagnetic minerals in rocks and lead to acquisition of a chemical remanent magnetization (CRM). One common alteration process is the submarine weathering that occurs at mid-ocean ridges. My previous laboratory simulation of CRM in single-phase oxidation of titanomagnetites like those in submarine basalts represents an important advance in understanding low-temperature alteration of the oceanic crust and its effect on linear magnetic anomalies.

Of particular current CRM interest is phase-coupled CRM, by which the remanence can be coupled to the pre-existing remanence of a parent phase. The objective is to understand magnetostatic or exchange interactions at the interface between two different magnetically ordered systems. It is a complex magnetic process and depends critically on the atomic-level chemical and spin structure at the interface. The experimental program involves laboratory studies under controlled time-temperature conditions in which CRM response to field direction and strength, and to prior remanence in the pre-existing phase, were carefully monitored.

Other current projects include magnetic domain structures on ferrimagnetic single crystals and the interactions of domain walls with crystal defects and their stress fields. The wall-defect interaction is an important mechanism in understanding how stable remanence originates in magnetic crystals much larger than single-domain size.

Another area of interest is low-temperature phase transitions in antiferromagnetic and ferrimagnetic crystals. The highlight of this study is that small deviations from stoichiometry in magnetite have a significant effect on the crystallographic phase transitions. This technique provides a sensitive probe for detecting low-temperature oxidation in lake and ocean sediments, soils and in loess/paleosol deposits which carry high-resolution paleoclimatic and paleoenvironmental information.

Selected Publications

Özdemir, Ö., and D. J. Dunlop, 2009.  Hallmarks of maghemitization in low-temperature cycling of partially oxidized magnetite nanoparticles. J. Geophys. Res., 114, 10.1029/2009JB006756, in press.

Özdemir, Ö., D. J. Dunlop and M. Jackson, 2009.  Frequency  and  field  dependent susceptibility of magnetite at low temperature. Earth Planet Sci. Lett. 61, 125-131.

Özdemir, Ö., D. J. Dunlop, and  T. S. Berquó, 2008.  Morin transition in hematite:  Size dependence and thermal hysteresis.  Geochem. Geophys. Geosyst., 9, Q10Z01, doi: 10.1029/2008GC002110.

Özdemir, Ö., 2008.  Thermoremanent magnetization, Encyclopedia of Geomagnetism and Paleomagnetism, Editors: David Gubbins and Emilio Herrero-Bervera.  Kluwer Academic Publishers, pp 609-616.

Dunlop, D. J., Ö. Özdemir, 2008.  Magnetization  in rocks and minerals, in Geomagnetism. Vol.5 edited by M. Kono.  In Treatise on Geophysics edited by G. Schubert, Elsevier, pp 277-236. 

Özdemir, Ö., and D. J. Dunlop, 2006.  Magnetic memory and coupling between spin canted and defect magnetism in hematite.  J. Geophys. Res., 111, B12S03, doi: 10.1029/2006JB004555. 

Özdemir, Ö., and D. J. Dunlop, 2006.  Magnetic domain observations on magnetite crystals in biotite and hornblende grains.  J. Geophys. Res., 111, B06103, doi:10.1029/2005JB004090.

Dunlop, D. J., Ö. Özdemir and D .G. Rancourt, 2006.  Magnetism of biotite crystals. Earth Planet. Sci. Lett., 243, 805-819.

Özdemir, Ö. and D. J. Dunlop, 2005.  Thermoremanent magnetization of multidomain hematite. J. Geophys. Res., 110, B09104, doi: 10.1029/2005JB003820.

Dunlop, D. J., B. Zhang and Ö. Özdemir, 2005.  Linear and nonlinear Thellier paleointensity behaviour of natural minerals.  J. Geophy. Res., 110, B01103, doi: 1029/2004JB003095.

Carvallo, C., D. J. Dunlop and Ö. Özdemir   2005.  Experimental comparison of FORC and remanent Preisach diagrams.  Geophys. J. Int., 162, 747-754. 

Carvallo, C., Ö. Özdemir and D. J. Dunlop, 2004.  First-order reversal curve (FORC) diagrams of elongated single-domain grains at high and low temperatures. J. Geophys. Res., 109, B04105, doi: 10.1029/2003JB002539.


÷zdemir,÷., and D.J. Dunlop, 2002. Thermoremanence and stable memory of single-domain hematites. Geophys. Res. Lett., 29, 10.1029/2002GL015597. [PDF]

÷zdemir, ÷., D.J. Dunlop and B.M. Moskowitz, 2002. Change in remanence, coercivity and domain state at low temperature in magnetite.  Earth Planet. Sci. Lett., 194/3-4, 343-358.[PDF]

Yu, Y., D.J. Dunlop and ÷. ÷zdemir, 2002. Partial anhysteretic remanent magnetization in magnetite:1. Additivity. J. Geophys. Res., 107, 10.1029/2001JB001249. [PDF]

Dunlop, D.J., and ÷.÷zdemir, 2001. Beyond Nťel theories: Thermal demagnetizationof narrow-band partial thermoremanent magnetizations. Phys. Earth Planet. Inter., 126, 43-57.  [PDF]

÷zdemir, ÷., 2000.  Coercive force of single crystal of magnetite at low temperatures.  Geophys. J. Int., 141, 351-356.  [PDF]

÷zdemir, ÷., and D.J. Dunlop, 2000. Intermediate magnetite formation during dehydration of goethite. Earth Planet. Sci. Lett., 177, 59-67. [PDF]

÷zdemir, ÷., and D.J. Dunlop, 1999. Low-temperature properties of a single crystal of magnetite oriented along principal magnetic axes. Earth and Planet. Sci. Lett., 165, 229-239.  [PDF]

÷zdemir, ÷., and D.J. Dunlop, 1998. Single-domain like behaviour in a 3mm natural single crystal of magnetite. J. Geophys. Res., 103, 2549-2562.  [PDF]

÷zdemir, ÷., and D.J. Dunlop, 1997. Effect of crystal defects and internal stress on the domain structure and magnetic properties of magnetite. J. Geophys. Res., 102, 20,211-20,224.  [PDF]

Dunlop, D.J., and ÷.÷zdemir, 1997. Rock Magnetism: Fundamentals and Frontiers, 573 pp., Cambridge University Press, New York, London and Cambridge.

÷zdemir, ÷., S. Xu and D.J. Dunlop, 1995. Closure domains in Magnetite. J. Geophys. Res., 100, 2193-2209.  [PDF]

÷zdemir, ÷., B.M. Moskowitz and D.J. Dunlop, 1993. The Effect of oxidation on the Verwey transition in magnetite. Geophys. Res. Lett., 20, 1671-1674.

÷zdemir, ÷., and D. York, 1992. 40Ar/39Ar laser dating of biotite inclusion in singe crystal of magnetite. Geophys. Res. Lett., 19, 1799-1802.

÷zdemir, ÷., and D.J. Dunlop, 1989. Chemico-viscous remanent magnetization in the Fe3O4 - γ Fe2O3 system. Science, 243, 1043-1047.

÷zdemir, ÷., and D.J. Dunlop, 1985. An experimental study of chemical remanent magnetizations of synthetic monodomain titanomaghemites with initial thermoremanent magnetizations. J. Geophys. Res., 90, 11513-11523.

÷zdemir, ÷., and S.K. Banerjee, 1982. A preliminary magnetic study of soil samples from West-Central Minnesota. Earth Planet. Sci. Lett., 59, 393-403.

÷zdemir, ÷., and W. O'Reilly, 1981. High temperature hysteresis and other magnetic properties of synthetic monodomain titanomagnetites. Phys. Earth Planet. Inter., 25, 406-418.