High field induced magnetic anisotropy of Al-substituted erbium iron garnet single crystals

Magnetic properties of garnet single crystals Er₃Fe_5-xAl_xO₁₂ (z=0.35 and 0.55) are reported under high magnetic field up to 230 kOe in the 4 K-300 K temperature range. The compensation temperature T_comp is shifted to higher temperature for increasing Al content: T_comp =80 K, 125 K and 152 K for z=0, 0.35 and 0.55 respectively. In the spontaneous state, the magnetic anisotropy is at most 5% in the 4 K-30 K temperature zone and weaker or absent at higher temperatures. [100] remains the “easy” axis for both Al contents. Using the Dionne-refined Neel model of ferrimagnetic garnets with Al³⁺ ions located in tetrahedral sites, the calculated temperature dependences of the spontaneous magnetization are in good agreement with experimental values. The strongly field dependent magnetic anisotropy of the garnets is important (up to 20%) only at low temperature (T<50 K). For both Al contents, the magnetic field stabilizes [100] as the “easy” axis. Furthermore, when H<30 kOe, Al substitution enhances [100] as the “easy” axis as compared to pure ErIG. Below T_comp in the high magnetic field zone (H>150 kOe), the onset of the usual canted magnetic phase takes place for H applied parallel to the [111] crystallographic axis