Large Uniaxial Anisotropy Induced in Soft Ferromagnetic Thin Films by Oblique Deposition of Underlayer

Abstract

We produced a large uniaxial anisotropy $(H_{k})$ in ultrathin (1.2–2.4 nm) soft ferromagnetic layers through the oblique deposition of a nanometer-thick metallic underlayer. Fe, Ni, and Ni80Fe20 (Permalloy) films deposited on a 5 nm thick Nb layer grown at an oblique angle (up to 60 ${}^{\circ}$ ) exhibit an $H_{k}\approx 40-500$ Oe and have properties that are nearly ideal for use as a fixed layer in magnetic devices, such as for magnetic memory. A much higher induced $H_{k}$ is observed in Ni (500 Oe) and Fe (300 Oe) compared to Ni-Fe (40 Oe). We used this technique to increase the switching field ( $H_{{\rm{sw}}}$ ) by 3–5 times in an array of pattered Fe or Ni-Fe bits, and achieved an excellent relative switching distribution of about 0.05–0.06. We also controllably enhanced the $H_{k}$ in the fixed layer of patterned spin-valve devices for superconducting Josephson-junction magnetic random-access memory and produced a large difference in $H_{{\rm{sw}}}$ between the fixed and free layers. Different spacer layers between the Nb and the magnetic layers either propagate (for Ru) or reduce (for Cu, Ru/Al, ion-milled Ru) the effect of the oblique Nb. This technique was also effectively used in synthetic antiferromagnet structures and, therefore, has the potential to eliminate the need for an antiferromagnetic pinning layer when it degrades magnetic device performance.