Search

Structural, microstructural and magnetic properties of polycrystalline Ni50Mn29Ga21 alloy are studied. Slight variations in processing parameters were employed to get large grain size and multimode twinning in polycrystalline alloy. The polycrystalline alloy shows significantly low detwinning stress of 19 MPa and high magnetic field induced strain of 0.7%. Presence of large grain size with multimode twinning, 7M modulated crystal structure, large magnetocrystalline anisotropy and high saturation magnetization are key factors for observation of large magnetic field induced strain in polycrystalline alloy. [ABSTRACT FROM AUTHOR]

We report here the coercivity (Hc) enhancement by way of surface diffusing Dy into the sintered Nd-Fe-B magnets, employing a novel and simple vapor deposition method. The beneficial effect on coercivity and the ominous effect on remanence were both studied and correlated with the time dependent Dy diffusion. The coercivity of Nd-Fe-B magnet is improved by partial substitution of Dy for Nd and described here is the surface diffusion method adopted to infiltrate Dy in to the sintered Nd-Fe-B magnet and the consequential effect on the microstructure and the magnetic properties. An 80% improvement in Hc occurred for four hours of Dy diffusion, while encountering a fall of about 11% in remanence. The SEM-EDS analysis brought out that Dy partition to a higher degree in to the Nd-rich grain boundary phase than the matrix Nd2Fe14B. [ABSTRACT FROM AUTHOR]

A systematic study of the effect of cobalt, selectively substituted for Ni and Mn, in the modulated orthorhombic (7M) Ni50Mn29Ga21 alloy has led to interesting correlations between the resultant structure and microstructure. Substitution of Co for Mn resulted in the stabilization of a non-modulated tetragonal (NM) phase at higher Co content and caused suppression of long-range twin deformation leading to sporadic islands within which twin variants were confined. On the other hand, substitution of Co for Ni does not to alter either the superstructural ordering or the long-range twin deformation. A study of the compositional dependence of saturation magnetization measured at 5 K is shown to throw light on the site preference of cobalt and iron atoms substituted in Mn-rich alloys of quasi-ternary Ni-Mn-Ga-(Fe,Co) system. The study reveals that the dopant atoms occupy the regular Mn site, rather than the vacant Ga site, with ferromagnetic exchange relative to the moments on Ni and Mn sub-lattices. These effects are attributed to have their origin in minimizing the stresses generated by the corresponding atomic volume changes incorporated by doping. [ABSTRACT FROM AUTHOR]

The partial substitution of Si with B on the structural and magnetic properties of Co2FeSi1-xBx (x = 0-0.5) alloys was systematically investigated. X-ray and microstructural investigations show the presence of second phase at the grain boundaries which increases with increasing boron content. From thermal analysis studies, it was observed that L21-B2 ordering temperature remain constant whereas the melting point decreases with increase in boron addition and merges with ordering temperature at x=0.5. The increase in TC for the alloys x ≥ 0.25 was attributed to the increase in second phase due to boron. [ABSTRACT FROM AUTHOR]

Boron addition to Ni53.5Mn26.0Ga20.5 alloy is found to modify the microstructure and mechanical properties substantially. Studies on (Ni53.5Mn26.0Ga20.5)Bx alloys reveal that boron addition causes grain refinement which led to an increase in compressive strength in x=0.5 alloy which also retained multimode twinning. Substantial second phase segregation rich in Ni was seen at grain boundaries, the extent of which increased with boron content. This led to a compositional shift in the matrix phase which resulted in a reduction in the martensitic transformation temperature and which in turn caused an easy deformation at low stresses and suppression of multimode twinning in x=1.0 alloy. [ABSTRACT FROM AUTHOR]

The effect of aging time on the magnetic properties of Sm2Co17 permanent magnets processed through a novel method of cold isostatic pressing was investigated. Sintered Sm2Co17 samples were subjected to different aging times in the range of 10-30 h and their respective microstructures were correlated with the magnetic properties obtained. The values of remanant magnetization (Br) were observed to be constant in samples aged from 10-20 h beyond which a gradual decrease in Br values was observed. The values of coercivity (Hc) displayed a sharp increase in samples aged from 10 to 20 h beyond which the coercivity values showed marginal improvement. Hence a good combination of magnetic properties could be achieved in samples aged for 20 h. A maximum energy product of 27 MGOe was achieved in the 20 h aged sample processed through a novel route. [ABSTRACT FROM AUTHOR]