Investigation of Magnetic Anisotropy and Barkhausen Noise Asymmetry Resulting from Uniaxial Plastic Deformation of Steel S235

This study investigates alterations in magnetic anisotropy and the marked asymmetry in Barkhausen noise (MBN) signals after the uniaxial plastic straining of steel S235 obtained from a shipyard and used as standard structural steel in shipbuilding. It was found that the initial easy axis of magnetisation in the direction of previous rolling, and also in the direction of loading, becomes the hard axis of magnetisation as soon as the plastic strain attains the critical threshold. This behaviour is due to the preferential matrix orientation and the corresponding realignment of the magneto-crystalline anisotropy. Apart from the angular dependence of MBN, the asymmetry in the consecutive MBN bursts at the lower plastic strains is also analysed and explained as a result of magnetic coupling between the grains plastically strained and those unaffected by the tensile test. It was found that, by increasing the degree of plastic strain, the marked asymmetry in MBN tends to vanish. Moreover, the asymmetry in MBN bursts occurs in the direction of uniaxial tension and disappears in the perpendicular direction. Besides the MBN technique, XRD and EBSD techniques were also employed in order to provide a deeper insight into the investigated aspects.

Structural, Magnetic and Microwave Absorption Characteristics of Ba1-xLaxFe12O19 (x = 0; 0.1; 0.2;0.3;0.5;0.7)

In this study, effect of La substitution on the microstructure, magnetic properties and microwave absorption characteristics of Ba1-xLaxFe12O19 (x=0, 0.1, 0.2, 0.3, 0.5, 0.7) is reported. The samples were synthesized through mechanical alloying and solid reaction a temperature 1200 °C for 2 hours. A single-phase material occurred only at x = 0 and 0.1. Additional second phases were existing in all samples with x ≥ 0.2 which led to multi-phase materials. The single phase (x = 0 and 0.1) has a relatively uniform particle size distribution with a mean crystallite size 138 nm. Additional phases of respectively Fe2O3 and LaFe2O3 were identified in all samples with x ≥ 0.2. Effect of La substitution is to decrease the magneto crystalline anisotropy constant and the saturation magnetization. The latter is due to a decrease in mass fraction of the main magnetic phase. All Ba1-xLaxFe12O19 samples have superior microwave characteristics which able to absorb more than 99 % the incoming electromagnetic wave entering the material. The absorption bandwidth is found relatively wide within the frequency range 8-12 GHz.

Conventional and Inverse Magnetocaloric Effect in Ni-Rich Ni-Mn-Ga and Ni-Mn-Sn Heusler Alloy: A Comparison

Magnetic and magnetocaloric effect of Ni-rich Ni52Mn34Sn14 (Ni-Mn-Sn) and Ni54Mn17Ga29 (Ni-Mn-Ga) Heusler alloys have been investigated up to a magnetic field of 5T and within a temperature range of 4.2 – 325 K. In this study, we report a systematic comparison between Ni-rich Ni52Mn34Sn14 and Ni54Mn17Ga29 alloys in the light of their magnetocaloric effect (MCE). In both the samples, a large magnetic entropy change was observed (~96 J kg-1 K-1 for Ni-Mn-Ga), but for the alloy Ni-Mn-Sn the MCE becomes negative/inverse. From various magnetic measurements it have been observed that in Ni-Mn-Sn alloy the martensite to austenite transition accompanied by lower to higher magnetization whereas for Ni-Mn-Ga alloy reverse situation occurred. The different type of magnetocaloric effect, i.e. inverse and direct can be explained by considering magneto-crystalline anisotropy and different state of magnetization of the martensite and austenite phase of the alloys.

Rare earth ion contribution in barium hexaferrite structure to a change of magnetocrystalline anisotropy to improving its magnetic properties

Rare earth ion contribution in barium hexaferrite structure to a change of magneto-crystalline anisotropy to improving its magnetic properties has been investigated. A series of simples of Ba1-xCexFe12O19 with the variation of x (x = 0.0-0.5) were prepared by solid-state reactions using mechanical deformation techniques. The oxide materials used for sample preparation are BaCO3, Fe2O3, and CeO2 with the ratio of material used is adjusted to the stoichiometric calculation for variations of Ce4+ substitution. The phase identification results show that the reaction took place perfectly and successfully formed a single-phase Ba1-xCexFe12O19 namely at the composition x = 0 and x = 0.1. while for the composition x> 0.1, it is formed in three phases. Particle morphology in the composition x = 0 and x = 0.1 has very good and uniform particle homogeneity across the surface of the sample in the form of polygonal particles. So the substitution of Ce atoms into the barium hexaferrite structure is only able at the composition limit x = 0.1. In the composition x = 0.1 has been able to increase the coercivity and magnetization fields. It can be concluded that the permanent magnet with the composition Ba0,9Ce0.1F12O19 gives the best results.