Antiferromagnetism, ferromagnetism and magnetic phase separation in Bi₂Sr₂O₆₊[delta]

Neutron scattering, magnetization and transport measurements were performed on single crystals of Bi2Sr2CoO6+[delta] to study the evolution of the magnetic properties as a function of the oxygen content . The oxygen content was varied by annealing single crystals in either a reducing or oxidizing environment to obtain an experimental range of 0.25 =/< [delta] =/< 0.5 and a corresponding average Co valence between +2.5 and +3. We show that the as-grown samples, which are oxygen rich ([delta approximately] 0.5) and therefore contain mostly Co3+ ions, enter an antiferromagnetic (AF) phase with a Neel temperature - 250 K. On the other hand, annealing as-grown crystals in vacuum to reach [delta approx.] 0.25 destroys the AF phase; these samples exhibit predominantly ferromagnetic (FM) behavior with Tc [approx.] 100 K. At intermediate doping, 0.25 < [delta] < 0.5, we find evidence for co-existence of FM and AF domains, which are characteristic of the [delta] = 0.25 and [delta] = 0.5 phases, respectively. The signature of the co-existence is the presence of simultaneous FM and AF magnetic Bragg peaks in the neutron diffraction pattern. Polarized neutron scattering measurements confirm that the FM and AF peaks do not arise from different components of a canted antiferromagnet.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2003

Author dc:creator

• Thomas, Kennedy Jessica, 1975-

Advisor dc:contributor.advisor

• Marc A. Kastner.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/29312

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/29312