Magnetic studies at low and intermediate temperatures
This thesis contains three major areas of work. Chapter 1 describes the various film deposition techniques available for the growth of thin films. These different growth methods, substrate preparation and vacuum techniques, are discussed in the context of the effect of the growth process and deposition environment on film structure and quality. Chapter 2 describes the two film growth chambers. Chapter 3 describes the origin of giant magnetoresistance (GMR) in magnetic multilayered structures, and investigates the magnetoresistive properties of ion-beam sputtered CoCu multilayered thin films. Different film structures and deposition conditions have been investigated in order to maximise the size of negative magnetoresistance seen. Chapter 4 investigates the magnetic and giant magnetoresistive properties of sputtered CoCu and CoAg heterogenous alloys. The magnitude of the GMR effect is found to depend on the Co concentration and Co particle size. Chapter 5 describes an investigation of molecular beam epitaxy (m.b.e.) grown Dy/Y multilayer structures. The temperature dependences of helical magnetic structure in the Dy layers is investigated in two samples of different multilayer structures. Chapter 6 describes an acoustic interferometer which has been used to measure velocity and attenuation changes in an ultrasonic signal at frequencies of order IGHz. Also described is the production of the thin film piezoelectric transducers used in this technique, which are grown directly onto a single crystal of the material under investigation. The acoustic interferometer is used to investigate the dynamics of of a relaxation process between two time-reversed antiferromagnetic states in DyAlG, and a model for domain growth in this system is postulated. Chapter 7 investigates the phase diagram of DyPO4 using the acoustic interferometry technique. The observations of hysteresis effects are used to define a mixed phase region below the tricritical point.