Systematic control of stress-induced anisotropy in pseudomorphic iron garnet thin films

Iron garnets are one of the most well-studied magnetic materials that enabled magnetic bubble memories and magneto-optical devices employing films with a perpendicular easy axis. However, most studies have been conducted on rather thick films ( > 1 mu m), and it has not been elucidated whether it is possible to align the magnetic easy axis perpendicular to the film plane for much thinner (< 100 nm) films by overcoming shape anisotropy. We studied the effects of epitaxial strain and film composition on the magnetic properties of 50-nm-thick garnet thin films grown by pulsed-laser deposition. Y(3)Fe(5)o(12) was selected as the most prototypical garnet and Sm3-xTmxFe5O12 (x=1, 2, 3) was selected in view of its negatively large magnetostriction constants. We employed (111) planes of single crystalline Gd3Ga5O12 and (CaGd)(3)(MgGaZr)(5)O-12 substrates to tune the epitaxial strain. Thin films with a pseudomorphic structure were fabricated with the in-plane strain (epsilon(parallel to)) ranging from -1.5% to +0.5%, corresponding to the stress-induced anisotropy field (H-A) ranging from -40 kOe to +25 kOe, respectively. The magnetization ratio of the out-of-plane to in-plane component (M-perpendicular to/M-parallel to) systematically varied in accord with H-A, yielding M-perpendicular to/M-parallel to > 1 for thin films with H-A values larger than 20 kOe. Among the films grown, Tm3Fe5O12 on Gd3Ga5O12 showed the largest epsilon(parallel to) and H-A values of +0.5% and +25 kOe, respectively, to realize an apparently perpendicular easy axis, confirmed by a large M-perpendicular to/M-parallel to value of 7.8. Further, magnetic force microscope images showed a maze pattern typical of a perpendicularly magnetized film. These results reveal a method for tailoring the magnetic anisotropy of garnet ultrathin films by utilizing epitaxial strain. These thin films may be utilized to obtain nanoscale magnetic bubbles for use in novel devices. (C)2013 Elsevier B.V All rights reserved.