| The temperature dependence of the exchange bias effect, a phenomenon due to the interfacial exchange coupling at the antiferromagnetic-ferromagnetic (AFM-FM) interface, is studied experimentally using CoO/Co bilayers with two different methods: magnetic hysteresis loop and magnetotransport. The exchange bias coupling in the CoO/Co gives rise to induce unidirectional anisotropy in the Co layer causing a shift in the magnetic hysteresis loops. The experimental results show that the exchange bias field decreases with increasing temperature and depends on the Co thicknesses. The exchange bias shift is inversely proportional to the ferromagnetic film thickness confirming that it is an interfacial effect. The large training effect in hysteresis loops indicates that the hysteresis loop method underestimates the unidirectional anisotropy induced by the exchange coupling. The exchange bias is also determined by measuring the anisotropic magnetoresistance (AMR). While previous measurements relied on two separate apparati for comparison, this experiment demonstrates that hysteresis loop measurements and AMR measurements can be performed in one system, the automated Physical Property Measurement System by Quantum Design. A greater magnitude in the exchange anisotropy energy is observed for measurements made with AMR compared to that of the hysteresis loop measurements. |
