The temperature dependence of the anisotropy field and coercivity in epitaxial films of mixed rare-earth iron garnets

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Abstract
The temperature dependence of the anisotropy field Hk and the domain‐wall coercivity Hc have been measured for three different epitaxial films of mixed rare‐earth iron garnets with the nominal compositions Er2Eu1Ga0.7Fe4.3O12, Y1Eu1.85Yb0.15Al1.1Fe3.9O12, and Eu1.7Er1.3Al0.7Ga0.8Fe3.5O12. Each of these garnets supports bubble domains. The anisotropy field was measured using an optical magnetometer, and analytical expressions are developed which relate the optical magnetometer parameters to the anisotropy field. These measurements show that the anisotropy field decreases with increasing temperature at about −1%/°C at 20°C for all three samples. The coercivity, again measured by an optical technique, was also found to decrease with increasing temperature. The coefficient ranged from −1.3%/°C to −3.0%/°C at 20°C depending on the sample. The largest total change in Hc for one of the samples was a factor of 310 over the temperature range −106°C to +80°C. The temperature variation of the saturation magnetization 4πMs and the material length l were also measured. The temperature coefficients of 4πMs and l at 20°C varied from ∼0.03%/°C to −1.1%/°C, and −0.9%/°C to 0.5%/°C, respectively. No simple correlation is evident among the temperature dependences of Hk, Hc, and 4πMs although l varies predictably with 4πMs and Hk. The large variations in coercivity are not consistent with simple conventional models.