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The effect of substrate and post-annealing temperatures on the structure, microstructure, residual stresses and soft magnetic properties of Fe 70 Co 30 thin films was systematically investigated. Microstructural studies reveal that the films are continuous and undergo changes in shape of grain from plate like to spherical resulting in an increase in grain size with the increase in substrate temperature, whereas the post-annealed films show small pores and no significant grain growth till 500 °C. Coercivity ( H c ) was found decreasing with both the substrate and post-annealing temperatures; however, the best H c value of 26 Oe was obtained for the films deposited at substrate temperature of 500 °C. The post-annealed films exhibited relatively higher H c values. A good combination of high saturation magnetization 4πM s of ~23.2 kG and low coercivity H c of 26–65 Oe was obtained for the films deposited at substrate temperature of 450–500 °C. Residual stress analysis on films with different substrate temperatures shows the presence of tensile stress. The decrease in tensile stress is attributed to the relaxation of thermal stresses in the films. [ABSTRACT FROM AUTHOR]

The influence of Ga on the structural, magnetic and half-metallic properties of Co 2 FeSi 1− x Ga x (0≤ x ≤1) thin films grown on Si (100) substrates using ultra high vacuum magnetron sputtering has been systematically investigated. The linear increase in cubic lattice parameter from 5.63 Å to 5.73 Å and the Curie temperature ( T C ) from 854 K to 941 K with x varying from 0 to 1 indicate the progressive substitution of Ga for Si. The coercivity ( H c ) was found to decrease from 26 Oe ( x =0) to 3 Oe ( x =1) at room temperature and is attributed to the decrease in magnetic anisotropy. The magnetic hysteresis loops measured from 300–873 K revealed that the film where Ga completely replaces Si exhibit better stability in both saturation magnetization ( M s ) and H c with temperature. The increase in coercivity at higher temperatures is attributed to the film to substrate interaction. The measured M s at 100 K decreases from 5.01 µ B /f.u. ( x =0) to 4.49 µ B /f.u. ( x =1) and follows the trend of Slater-Pauling rule. The indirect evidence of half-metallic nature is examined from the temperature dependent electrical resistivity measurements. [ABSTRACT FROM AUTHOR]

Abstract: Investigations on Ni53.5Mn26.0Ga20.5B x system with x = 0, 0.5 and 1.0 show that boron addition does not alter the monoclinic crystal structure, but modifies the superstructural ordering of the boron-free parent compound. Observed reduction in the martensitic transformation temperature by nearly 30 K differs from the usual trend expected with a rise in electron concentration. Contrary to the reports on Ni–Mn–Ga alloys with boron substitution, saturation magnetization at low temperatures increases substantially (∼19% per formula unit) on boron addition. The observed large rise in magnetization is correlated to the compositional shift in the majority matrix phase caused by the secondary phase segregation at the grain boundaries, promoted by addition of B. Formation of Ni-rich secondary phase and the associated reduction in Ni content in the matrix phase results in redistribution of Mn atoms at Mn and Ga sites. This causes an effective change in the balance between Mn moments with ferro- and anti-ferromagnetic order in the unit cell, thus explaining the magnetic properties. [Copyright &y& Elsevier]

Abstract: Results from a systematic study of the effect of cobalt, selectively substituted for Ni and Mn, in the modulated orthorhombic (7M) Ni50Mn29Ga21 alloy are contrasted. Substitution of Co for Mn resulted in the stabilization of a non-modulated tetragonal (NM) phase at higher Co content. At lower Co contents, a mixture of 7M and NM phases were found to co-exist. Increasing in Co content caused suppression of long-range twin deformation leading to sporadic islands within which twin variants were confined. These effects are attributed to the considerable stresses generated by an atomic volume change of 9.5% caused locally when Co is substituted for Mn. On the other hand, substitution of Co for Ni, which causes only 1.7% atomic volume change locally, was observed not to alter either the superstructural ordering or the long-range twin deformation. Our results show that the microstructures resultant on Co doping have a strong correlation to the structural ordering, which in turn depends on whether Co is substituted for Mn or for Ni, and also on the concentration of Co. [Copyright &y& Elsevier]

We report a seven-layered modulated monoclinic crystal structure in the Ni-rich, Ga-poor Ni53.5Mn26.0Ga20.5 alloy. The present composition exhibits coupled magneto-structural transformation around 350K. Multi-mode twinning with a predominance of crossing twins, indicative of low residual stresses, is observed. A significant shape memory effect of 1.6% and a high strain recovery ratio of 89% are achieved in the polycrystalline specimen at low stresses, owing to lower twinning energies arising from lattice modulation. [ABSTRACT FROM AUTHOR]

• The influence of boron in Co 2 FeSi 1−x B x (x = 0–0.5) Heusler alloys was systematically investigated. • The x-ray diffraction and microstructural analysis confirmed the presence of second phase. • The melting point decreases with increasing boron and merges with ordering temperature at x = 0.5. • The observed compositional shift with boron content is attributed to the formation of second phase. The influence of partial substitution of boron on the structural, microstructure, magnetic and calorimetric properties of Co 2 FeSi 1−x B x (x = 0–0.5) alloys was systematically investigated. The x-ray powder diffraction and microstructural analysis confirmed the presence of second phase in the alloys. From calorimetric studies, it was observed that L2 1 –B2 ordering temperature remain constant whereas the melting point decreases with increasing boron content and merges with ordering temperature at x = 0.5. The Curie temperature (T C) for the alloys x ≥ 0.25 has shown a linear increase with boron concentration. The saturation magnetic moment exhibits a linear decrease and confirms the substitutional effect of boron for Si. With increase in boron content, a compositional shift has been observed which may be attributed to the formation of second phase at the grain boundaries. [ABSTRACT FROM AUTHOR]

The effect of processing parameters such as argon gas pressure (5, 10 and 15 mTorr) and sputtering power (50 and 100 W) on the structure, microstructure and magnetic properties of dc magnetron sputtered Tb–Fe–Co films was investigated. X-ray diffraction studies indicate that all the films were found to be amorphous in nature irrespective of the deposition conditions. The increase in sputtering gas pressure and power was found to deplete the transition metal content in the films. Room temperature ferromagnetism accompanied with low coercivity (20 Oe) and low saturation magnetic field has been achieved for the film grown at 5 mTorr gas pressure and 50 W sputtering power. The microstructure of Tb–Fe–Co films showed the presence of islands, whose size increased with increasing sputtering power and argon gas pressure. Magnetization studies indicated that all the films were magnetically ordered up to room temperature. A compensation temperature was observed for the films grown at higher gas pressure and sputtering power. Annealing of the films did not result in any crystallization and as a consequence the magnetic properties were found to remain unaltered. [ABSTRACT FROM AUTHOR]

NiO thin films were grown systematically using the nebulizer spray pyrolysis (NSP) method with different additions of Ag 1%, 2%, and 3% respectively. A photodetector was fabricated using NiO:Ag thin films. The structural, morphological, compositional, optical, and electrical properties of NiO:Ag thin films were studied as a function of Ag addition. XRD studies show a gradual reduction in the intensity and the broadening with Ag addition, which confirms the formation of nanoparticles. Ag phase has been formed after 3% of Ag addition. Compositional studies using EDS confirms the presence of all the elements. The energy band gap of films is found to be in the range 3.25–3.45 eV with an Ag addition of 1–3%. I–V characteristics and photoresponse of photodetectors were recorded under UV light illumination. The parameters of a photodetector such as external quantum efficiency, responsivity and detectivity were calculated. The observed photo responsivity increases with an increase of Ag (1%) and decreases further higher Ag concentrations.The maximum responsivity is observed for the NiO film with 1%Ag. The photoresponse of all samples confirmed the stable and reproducible characteristics such as external quantum efficiency, responsivity and detectivity.The enhanced properties observed for 1% of Ag-doped film may find applications in the fabrication of optoelectronic devices. [ABSTRACT FROM AUTHOR]