科研之友
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摘要
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.
- 出版日期2013-8
