Significantly enhanced anisotropic magnetoresistance (MR) in permalloy (Ni0.81Fe0.19) films deposited on a thin (Ni0.81Fe0.19)1−xCrx or Ni1−xCrx underlayer is reported. The maximum ΔR/R enhancement was observed using the underlayer with x≈0.44 at an optimum thickness of ≈30–45 Å, depending on the deposition technique. An enhancement of 75%–150% was observed for 45–430 Å thick permalloy films, compared to the films deposited without this underlayer. The ΔR/R enhancement is attributed to the decrease in the resistivity ρ and the increase in Δρ of the permalloy film due to the formation of large (111) textured crystal grains in the permalloy films deposited on this underlayer, as revealed by the x-ray diffraction results obtained using synchrotron radiation.
The structural and magnetic properties of off-stoichiometric 2:17-type compounds Sm2Fe17−xTxM (T=Co, Ti; M=Al, Si; x=0–4) were studied by x-ray powder diffraction, thermomagnetic analysis, and magnetic measurements. All these compounds were of the Th2Zn17 type. The substitution of Co or Ti for Fe, and the addition of Si or Al into the Sm2Fe17 did not alter the rhombohedral structure. The Co replacement increased the Curie temperature Tc due to the strong coupling between Fe and Co. A small substitution of Ti also led to an increase of Tc. However, when x>3, the exchange coupling became less effective as the separation between the Fe atoms became large, and Tc decreased. The maximum Tc=713 K was found in Sm2Fe17−xCoxSi when x=4. As for the saturation magnetization Ms, Sm2Fe17−xTixAl had its Ms decreased monotonically with increasing Ti, while Ms of other compounds increased first and then decreased with the content of Co or Ti. The maximum Ms=159 emu/g was recorded in Sm2Fe15Co2Al. To make use of these compounds as permanent magnets, Sm2Fe15Co2Si is preferred because it has Tc=641 K and Ms=142 emu/g. The dual substitutions of Fe by using Co or Ti, and by Al or Si to improve Tc and Ms of Sm2Fe17, are more effective than using single substitution.
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