Exchange Bias And Coercive Field Of The Monte-carlo Study. Ferromagnetic / Antiferromagnetic Bilayers

The magnetoresistance arising from the Ferromagnetic (FM) multilayered systems has been greatly applied in the field of the magnetic memorization and the magnetic sensor. Recently, the exchange bias, which can enhance the magnetoresistance, has been found in the FM/AFM systems, so the FM/AFM systems have aroused people's considerable interests.Based on Monte Carlo method, doping nonmagnetic matter in antiferromagnetic layers of the FM/AFM bilayers, the temperature dependence of the exchange bias and coercivity in FM/AFM bilayers is investigated by changing grain size and nonmagnetic doping concentration. In addition, by changing the shape of the interface between FM and AFM layers, we explored the relation between interface microstuctue and the exchange bias and the coercivity. The main content is described as follows:1 By changing nonmagnetic diluted concentration in the AFM, the temperature dependence of exchange bias is discussed in FM/AFM bilayers of plane type. The simulative results show that the exchange bias in FM/AFM bilayers can be enhanced significantly by substituting nonmagnetic atoms into the AFM layers. And there is a maximum in the sketch of exchange bias as a function of the diluted concentration, i.e. the exchange bias firstly increases then decreases with increasing concentration of dilution at the same temperature. Besides, the maximum of the exchange bias occurs at lower concentration for the higher temperature. These are agreed with the results of Phys. Rev. Lett. 96 117204(2006). The cause of these results is that the spin distributing and the magnetic domain structure are greatly changed with varying diluted concentration. The exchange bias approaches maximum when the positive magnetic domain and the negative one form the connected network structure.2 The effect of changing grain size of the antiferromagnetic layers on the exchange bias and the coercivity is studied in FM/AFM bilayers of plane type by Monte Carlo method. The simulative results show that the velvet pitch of hysteresis is reduced along with increasing grain size but the rectangle pitch is increased. At the same temperature, the relation between exchange bias and grain size is very complicated, however, the coercivity changed little when grain size increased to a fixed value. At the same diluted concentration, both the exchange bias and the coercivity decrease along with increasing temperature and finally approach to zero, but there is a little difference in the reducing of velocity.3 When the shape of the interface between FM and AFM layers is plane, step and hackle, respectively, we studied the relation between diluted concentration and the exchange bias and the coercivity, and also separately get the temperature dependence of the exchange bias and the coercivity. The simulative results show that at the same concentration of dilution, the exchange bias of the FM/AFM bilayers of plane type interface is much larger than the other two systems but the coercivity is smaller. And the exchange bias and the coercivity of both the step type and the hackle type are much the same. Besides, we did much research on changing the grain size of antiferromagnetic layers, the results are similar but the numerical values aren't the same. In addition, we interestingly found that by changing the interface type between FM and AFM layers, the exchange bias and coercivity in FM/AFM bilayers is visibly changed, which also ulteriorly indicated that the characteristic of exchange bias in FM/AFM systems depends on the interface microstructure.