Experimental Magnetism

Prof. Robert P. Guertin Prof. Yaacov Shapira We are measuring the response of a variety of metallic transition metal oxides, intermetallic compounds, dilute magnetic semiconductors, and small magnetic clusters in organic molecules, to extreme environments of high magnetic fields, low temperatures, and high pressures, which can radically alter their electrical and magnetic properties.

Experimental techniques include high field magnetometry, temperatures as low as 20 mK, transport measurements, heat capacity, and magnetostriction. Many of the projects are carried out collaboratively. Present collaborations include groups at MIT, at the National High Magnetic Field Laboratory in Tallahassee, Florida, at the University of São Paulo, Brazil and at the University of Montpellier, France. The laboratories at Tufts itself include a SQUID magnetometer, a vibrating sample magnetometer with a 9T superconducting magnet, and several transport property cryostats. The metallic transition metal oxides undergo precipitous changes between metallic and insulating phases, normal and superconducting phases, and paramagnetic and ferromagnetic phases. These materials have non-linear characteristics that make them useful for a variety of electronic devices. Dilute magnetic semiconductors (DMS) are semiconductors in which a fraction of the cations has been replaced by magnetic ions, and exhibit complex and interesting magnetic properties. Exchange interactions are determined using the new magnetization-steps method. Various effects which arise from bound magnetic polarons in DMS are investigated experimentally. Interactions within small magnetic clusters which occur in some organic molecules are studied using magnetization steps in pulsed magnetic fields. Model calculations relating to all these experiments are being carried out.

 Selected Publications:

"Magnetization and Magnetotransport of LnBaCo2O5.5 (Ln=Gd, Eu) Single Crystals" (with Z. X. Zhou, S. McCall, C. S. Alexander, J. E. Crow, P. Schlottmann, S. N. Barilo, S. V. Shiryae and G. L. Bychkov). Accepted by Phys. Rev. B.
 
"Magnetically Complexed Collagen Nanocomposites" (with R. Valluzzi and T. E. Haas). To be published in Phil. Mag.

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