We show tunable strain-induced perpendicular magnetic anisotropy (PMA) over a wide range of thicknesses in epitaxial ferrimagnetic insulator Eu3Fe5O12 (EuIG) and Tb3Fe5O12 (TbIG) thin films grown by pulsed-laser deposition on Gd3Ga5O12 with (001) and (111) orientations, respectively. The PMA field is determined by measuring the induced anomalous Hall loops in Pt deposited on the garnet films. Due to positive magnetostriction constants, compressive in-plane strain induces a PMA field as large as 32.9 kOe for 4 nm thick EuIG and 66.7 kOe for 5 nm thick TbIG at 300 K, and relaxes extremely slowly as the garnet film thickness increases. In bilayers consisting of Pt and EuIG or Pt and TbIG, robust PMA is revealed by squared anomalous Hall hysteresis loops in Pt, the magnitude of which appears to be only related to the net magnetic moment of iron sublattices. Furthermore, the magnetostriction constant is found to be 2.7x10^(-5) for EuIG and 1.35x10^(-5) for TbIG, comparable with the values for bulk crystals. Our results demonstrate a general approach of tailoring magnetic anisotropy of rare earth iron garnets by utilizing modulated strain via epitaxial growth.
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