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Title: Magnetic properties of Gd-Lu alloys, Er and a Ho90Er10 alloy
Author: Eccleston, Roger Soulsby
ISNI:       0000 0001 3438 0302
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1991
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Two quite different facets of rare earth magnetism have been studied using neutron elastic scattering and ultrasound velocity and attenuation measurements. A new automated ultrasound measurement system gives an improvement in precision on other measurement techniques and has been shown to be well suited to the measurement of both the temperature and magnetic field dependence of ultrasonic elastic constants and their associated attenuation coefficients. The zero field magnetic phase diagram of the Gd-Lu alloy system has been studied in the vicinity of the multicritical region. New detail has been added to the existing phase diagram. Ultrasound data provides strong evidence for the existence of a ferro-I phase, which displays a net moment along the c-axis while being apparently paramagnetic in the basal plane. A helical antiferromagnetic phase exists for those samples with a Lu concentration of greater than 23.5%. The turn angle of the helix appears to decrease continuously on cooling and tends to zero as the transition to a canted ferromagnetic phase is approached. The transition comes about as ferromagnetic domains grow out of antiferromagnetic domain walls. The behaviour of a Gd76.oLu24.o alloy in an applied magnetic field has been studied, permitting the construction of applied field-temperature phase diagrams relating to fields applied parallel to the a-axis and parallel to the c-axis. Both reveal several unexpected features particularly in the ferro-I region. The ultrasonic elastic constants of erbium show anomalous behaviour as a result of the formation of high order commensurate structures made up of spin-slips. Those commensurate structures which display a net ferromagnetic moment are seen by neutron diffraction to become stable over limited temperature ranges, in good agreement with previous X-ray data. Both the neutron scattering and the ultrasound data show evidence of a subtle change in the magnetic structure immediately above Tc. The temperature dependence of the ultrasonic elastic constants of the random alloy HogoErio have been measured. A limited neutron diffraction experiment shows that the addition of 10% Er produces quite considerable departures from the magnetic behaviour of pure Ho. Ultrasonic measurements performed on Er in a c-axis applied magnetic field permit the construction of a tentative phase diagram which shows that the commensurate phases with a net ferromganetic moment become more stable. Two conical ferromagnetic cone phases are observed, in addition to the cone phase observed in zero field.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics