Magnetic properties of Sm(Co/sub bal/Fe/sub 0.31/Zr/sub 0.05/Cu/sub 0.04/B/sub x/)/sub z/ alloys and their melt-spun materials (x=0.02--0.04,z=7.5--12)
Cast alloys and melt-spun ribbons with nominal compositions of Sm(Co/sub bal/Fe/sub 0.31/Zr/sub 0.05/Cu/sub 0.04/B/sub x/)/sub z/ (x=0.02-0.04,z=7.5-12) have been synthesized and characterized in a temperature range of 10-1273 K and at fields up to 5T. The main phase in the as-cast alloys exhibited a Th/sub 2/Ni/sub 17/ type structure, with a strong uniaxial anisotropy. Minor phases with a TbCu/sub 7/ and/or CaCu/sub 5/ structure emerged as z (3d/R) decreased. As a result, the anisotropy field (H/sub A/) increased from 67 to 120 kOe, while 4/spl pi/M/sub s/ fell from 12.8 to 10.5 kG at 300 K when z was decreased from 12 to 7.5. For melt-spun ribbons, they are nano-structured in nature and magnetically hard, even in the as-spun state. By lowering the value of z(3d/R) and raising the B content, a finer microstructure and a higher H/sub ci/ were obtained. Hard magnetic properties of H/sub ci/=4.9-12 kOe, 4/spl pi/M/sub s/=9.0-12.0 kG at 300 K have been obtained from ribbon samples. Among them, Sm(Co/sub bal/Fe/sub 0.31/Zr/sub 0.05/Cu/sub 0.04/B/sub 0.02/)/sub 10/ ribbon showed the highest (BH)/sub max/ of 10.8 MGOe at 300 K. A Henkel plot analysis suggested the existence of exchange-coupling interaction between the magnetically hard and soft phases in the ribbon materials.
Investigation of magnetization reversal processes in Sm(Co, Fe, Cu, Zr)7.5 magnets
The processes of magnetization reversal in isotropic and anisotropic commercial permanent magnets Sm(Co, Fe, Cu, Zr)7.5 were investigated. Features of magnetization reversal process in both textured and isotropic magnets were analyzed with δM(H) plots, magnetic susceptibility and initial magnetization curves. The magnetization reversal of Sm(Co, Fe, Cu, Zr)7.5 magnets is more complicated than that described in the coercivity model based on the domain walls pinning.
Asymptotic Properties of Solutions to Second-Order Difference Equations of Volterra Type
<jats:p>We consider the discrete Volterra type equation of the form <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mi mathvariant="normal">Δ</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mrow><mml:mi>r</mml:mi></mml:mrow><mml:mrow><mml:mi>n</mml:mi></mml:mrow></mml:msub><mml:mi mathvariant="normal">Δ</mml:mi><mml:msub><mml:mrow><mml:mi>x</mml:mi></mml:mrow><mml:mrow><mml:mi>n</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>=</mml:mo><mml:msub><mml:mrow><mml:mi>b</mml:mi></mml:mrow><mml:mrow><mml:mi>n</mml:mi></mml:mrow></mml:msub><mml:mo>+</mml:mo><mml:mrow><mml:msubsup><mml:mo stretchy="false">∑</mml:mo><mml:mrow><mml:mi>k</mml:mi><mml:mo>=</mml:mo><mml:mn mathvariant="normal">1</mml:mn></mml:mrow><mml:mrow><mml:mi>n</mml:mi></mml:mrow></mml:msubsup><mml:mrow><mml:mi>K</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mi>n</mml:mi><mml:mo>,</mml:mo><mml:mi>k</mml:mi><mml:mo stretchy="false">)</mml:mo><mml:mi>f</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mrow><mml:mi>x</mml:mi></mml:mrow><mml:mrow><mml:mi>k</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:mrow></mml:math>. We present sufficient conditions for the existence of solutions with prescribed asymptotic behavior. Moreover, we study the asymptotic behavior of solutions. We use <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mi mathvariant="normal">o</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msup><mml:mrow><mml:mi>n</mml:mi></mml:mrow><mml:mrow><mml:mi>s</mml:mi></mml:mrow></mml:msup><mml:mo stretchy="false">)</mml:mo></mml:math>, for given nonpositive real <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:mrow><mml:mi>s</mml:mi></mml:mrow></mml:math>, as a measure of approximation.</jats:p>