Dynamic magnetic susceptibility of systems with long-range magnetic order

Date
2009-01-01
Authors
Vannette, Matthew
Major Professor
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Ruslan Prozorov
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Physics and Astronomy
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Physics and Astronomy
Abstract

The utility of the tunnel diode resonator (TDR) as an instrument for the study of magnetically ordered materials has been expanded beyond simple demonstration purposes. Results of static applied magnetic field dependent measurements of the dynamic magnetic susceptibility, χ, of various ferromagnetic (FM) and antiferromagnetic (AFM) materials showing a range of transition temperatures

(1-800 K) are presented. Data were collected primarily with a tunnel diode resonator (TDR) at different radio-frequencies (∼10-30 MHz). In the vicinity of TC local moment ferromagnets show a very sharp, narrow peak in χ which is suppressed in amplitude and shifted to higher temperatures as the static bias field is increased. Unexpectedly, critical scaling analysis fails for these data. It is seen that these data are frequency dependent, however there is no simple method whereby measurement frequency can be changed in a controllable fashion. In contrast,

itinerant ferromagnets show a broad maximum in χ well below TC which is suppressed and shifts to lower temperatures as the static bias field is increased. The data on itinerant ferromagnets are fit to a semi-phenomenological model that suggests the sample response is dominated by the uncompensated minority spins in the conduction band. Concluding remarks suggest possible scenarios to achieve frequency resolved data using the TDR as well as other fields to

which the apparatus may be applied.

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