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We report that the unusual behavior of anomalous Hall effect (AHE) in permalloy (Fe20Ni80, Py) thin film with silicon oxide (SiO2) as an adjacent layer. It is found that sign of AHE changes from positive to negative with decrement in thickness of Py. Through the AHE measurement, we demonstrate that this unusual behavior originates from the interface of Py/SiO2 rather from the structural inversion asymmetry. In the Pt/YIG/Cu/Py/SiO2 multilayer structure with a charge current injected in the Py layer, the information on spin accumulation at the YIG/Cu interface induced by the AHE in Py, can be obtained from the nonlocal voltage measured in the Pt layer. Through the nonlocal measurement, it is found, however, the electrons with same spin for interfacial Py near the SiO2 layer and bulk Py are scattered to the same direction. Hence we can deduce that the sign of spin polarization of the conductivity closely related to the asymmetry in density of states at the Fermi level for interfacial Py and bulk Py should be opposite to each other, which is responsible for the abnormal AHE observed. Our results demonstrate that oxide layer can drive the change of sign of AHE of Py, which provide an alternative way of manipulating the spin-related transport.

Recently antiferromagnetic materials become very attractive due to their new applications in spintronic devices. High-quality single crystal epitaxial ZnxCo1−xO (1 1 1) thin films were grown by co-evaporating Zn and Co and simultaneously oxidizing in oxygen plasma. It is found that the exchange bias fields of Co/as-prepared ZnxCo1−xO bilayers decrease with increasing Zn composition. When as-prepared ZnxCo1−xO layer was annealed in oxygen plasma to remove oxygen vacancies, the exchange bias field of Co/oxygen-plasma-annealed ZnxCo1−xO bilayers can be further enhanced. Moreover, a weak ferromagnetism was observed at 300 K in the as-prepared antiferromagnetic ZnxCo1−xO film with oxygen vacancies, but it did not exist in oxygen-plasma-annealed ZnxCo1−xO film. This indicates that oxygen vacancies can simultaneously weaken the antiferromagnetism but enhance the ferromagnetism of ZnxCo1−xO layer. Therefore, we offer a method of manipulating the antiferromagnetism of ZnxCo1−xO films by changing Zn composition and oxygen vacancies, which is useful for designing antiferromagnetic spintronic devices.

Heterostructures consisting of ferromagnetic metal and antiferromagnetic insulator have exhibited novel properties in interface exchange coupling, magnetoresistance and spin injection due to their fundamental physics of magnetism. However, as compared with bilayer heterostructures, it is very challenging in experiments to prepare single crystal epitaxial ultrathin superlattices consisting of ferromagnetic metal and antiferromagnetic insulator, where the interface exchange coupling, magnetic order, and electrical transport properties are expected to be greatly modulated due to the multiple interfaces and periodical structures. Here we prepared single crystal epitaxial [Co/CoO]n superlattices consisting of ferromagnetic metal Co and antiferromagnetic insulator CoO by molecular beam epitaxy. It is found that the saturation magnetization of [Co 0.6 nm/CoO 1.2 nm]5 superlattice is robust against temperature increase, which only shows a slight decrease of 1.5% from 5 K to 300 K. Moreover, we found that the longitudinal resistivity and anomalous Hall resistivity of [Co/CoO]n superlattices are strongly modulated by the short-period Co/CoO heterostructure, which are quite distinguished from the electrical transport properties of Co bulk ferromagnetic metal. The [Co/CoO]n superlattices provide a new insight into heterostructures consisting of ferromagnetic metal and antiferromagnetic insulator, which are beneficial for designing future spintronics devices.