Stress insensitive permalloys for memory application

Abstract

A description of the development of a family of high-squareness low-stress-sensitivity Permalloys of controlled coercive force for application as the soft magnetic element in the piggyback twister-type memory is given. Since both the hard- and soft-magnetic elements are wrapped simultaneously around the conductor core, the magnetic properties of both elements must be optimized by a single post-wrap annealing treatment. Previous work on a Co-Fe-Au alloy as the hard magnetic element has led to an annealing temperature range of 800-900°C, which must now be adopted for the treatment of the soft magnetic element as well. From published data on the compositional dependence of magnetocrystalline anisotropy and saturation magnetostriction in Ni-Fe-Mo alloys, an optimum composition, 6 percent Mo-80.5 percent Ni-13.5 percent Fe was first devised for which <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dB_{r}/d\sigma \simeq 0, B_{r}/B_{s} &gt; 0.9</tex> , and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H_{c} \simeq 0.3</tex> Oe after post-wrap annealing. By adding small amounts of Be (0.4-0.7 percent) or Zr (0.2-0.4 percent), the coercive force can be controlled to any value up to 3 Oe as a result of precipitation. At the same time, low stress sensitivity was retained and squareness improved.