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Abstract: The dependence of the magnetic and magnetoelastic properties of highly magnetostrictive cobalt ferrite on processing parameters has been investigated. The cobalt ferrite samples used in this study were prepared via conventional ceramic processing methods. The processing parameters of interest were sintering temperature, holding time at the sintering temperature and powder compaction pressure. It was observed that the crystal structure, composition and saturation magnetization of the samples studied did not vary with changes in processing parameters but coercive field decreased with increasing sintering temperature. The amplitude of peak to peak magnetostriction was dependent on the holding time and powder compaction pressure. The strain derivative on the other hand was found to depend on powder compaction pressure at any given sintering temperature or holding time. The results show how the magnetoelastic properties of cobalt ferrite can be varied by changing the processing parameters. [Copyright &y& Elsevier]

Abstract: Thermal expansion and magnetostriction of members of a homologous series of compounds based on the alloy series Pr( n +2)( n +1)Ni n ( n −1)+2Si n ( n +1) have been measured. The crystal structures of these compounds are closely interrelated because they form trigonal prismatic columns in which the number of trigonal prisms that form the base of the trigonal columns is determined by the value of n in the chemical formula. Two compositions were investigated, Pr5Ni2Si3 and Pr15Ni7Si10, corresponding to and respectively. The results were analyzed and used to determine the location of magnetic phase transitions by calculating the magnetic contribution to thermal expansion using the Gruneisen–Debye theory. This allowed more precise determination of the magnetic transition temperatures than could be achieved using the total thermal expansion. The results show two phase transitions in each material, one corresponding to the Curie temperature and the other at a lower temperature exhibiting characteristics of a spin reorientation transition. [Copyright &y& Elsevier]

Abstract: The Jiles–Atherton (JA) theory of hysteresis has been extended in the present paper to model hysteresis in two-phase magnetic materials. Two-phase materials are those that exhibit two magnetic phases in one hysteresis cycle: one at lower fields and the other at higher fields. In magnetic hysteresis, the transition from one phase to the other i.e. low field phase to high field phase depends mainly on the exchange field. Hence, the material-dependent microstructural parameters of JA theory: spontaneous magnetization, M S , pinning factor, k, domain density, a, domain coupling, , and reversibility factor, c, are represented as functions of the exchange field. Several cases based on this model have been discussed and compared with the measured data from existing literature. The shapes of the calculated and measured hysteresis loops are in excellent agreement. [Copyright &y& Elsevier]

Abstract: Determination of Curie temperature by plotting magnetic moment vs. temperature curves requires a small applied field, which influences the measurement and temporarily disturbs the temperature of the sample especially for highly magnetocaloric materials. The Arrott plot technique was therefore used in order to determine the Curie temperature for a magnetocaloric Gd5Si2.7Ge1.3 (x=0.675) single crystal sample. This technique was compared with other methods such as the inflection point technique and the line projection method. The results show how applied magnetic field influences the determination of Curie temperature. Using the Arrott plot the second-order transition Curie temperature for Gd5Si2.7Ge1.3 was determined to be 304K. [Copyright &y& Elsevier]

Abstract: The influence of different heat treatments on the magnetic and magnetoelastic properties of highly magnetostrictive CoFe2O4 has been investigated. The first order cubic anisotropy coefficient, coercive field, magnetostriction and high strain sensitivity were observed to decrease as the heat treatment temperature increased. The saturation magnetization of the samples on the other hand increased with increase in heat treatment temperature. These changes were not accompanied by any observable changes in crystal structure or composition and are indicative of migration of Co2+ from the octahedral sites (B-sites) to the tetrahedral sites (A-sites) and Fe3+ from the A-sites to the B-sites of the spinel structure. Different distributions of the cations at the two distinct lattice sites can strongly affect the magnetic and magnetoelastic properties of these materials. [Copyright &y& Elsevier]

Abstract: Differences in the microstructure and magnetic properties of highly magnetostrictive cobalt ferrite resulting from the effects of different vacuum sintering temperatures and times have been investigated. A vacuum environment was chosen to allow direct comparison of results with air-sintered samples which are more often reported in the literature. It was found that vacuum sintering resulted in the development of a solid solution second phase with composition Co1− x Fe x O4 (x∼0.33). There was a decrease in magnetostriction as a result of the formation of the second phase. Furthermore, differences in sintering temperatures were found to have a greater effect on the magnetostriction than differences in sintering times. It was found that the first order cubic anisotropy coefficient initially increased with both sintering temperature and time, before peaking and decreasing to its lowest measured value. The lowest anisotropy was therefore achieved with samples sintered at higher temperatures and longer times. [Copyright &y& Elsevier]

Abstract: Gd5(Si x Ge1−x )4, known for its giant magnetocaloric effect, also exhibits a colossal strain of the order of 10,000ppm for a single crystal near its coupled first-order magnetic–structural phase transition, which occurs near room temperature for the compositions 0.41≤x≤0.575. Such colossal strain can be utilised for both magnetic sensor and actuator applications. In this study, various measurements have been carried out on strain as a function of magnetic field strength and as a function of temperature on single crystal Gd5Si2Ge2 (x=0.5), and polycrystalline Gd5Si1.95Ge2.05 (x=0.487) and Gd5Si2.09Ge1.91 (x=0.52). Additionally a giant magnetostriction/thermally induced strain of the order of 1800ppm in polycrystalline Gd5Si2.09Ge1.91 was observed at its first order phase transition on varying temperature using a Peltier cell without the use of bulky equipment such as cryostat or superconducting magnet. [ABSTRACT FROM AUTHOR]