The spin polarization of Zn0.32Co0.68O1−v (v means oxygen vacancies) concentrated magnetic semiconductor (CMS) films was extracted from measurements of tunneling magnetoresistance (TMR), and spin-dependent variable range hopping, respectively. A TMR ratio of 19.1% was observed at 2 K in Co/ZnO/Zn0.32Co0.68O1−v magnetic tunnel junctions, which gives a low limit of the spin polarization of 25% in the Zn0.32Co0.68O1−v CMS. The TMR decreases with increasing temperature and bias voltage mainly due to the tunneling via localized impurity states in the barrier. By contrast, the spin polarization of the Zn0.32Co0.68O1−v CMS was estimated to be 36.1% by spin-dependent variable range hopping.

Homogeneous amorphous MnxGe1−x:H films were synthesized under thermal nonequilibrium condition by magnetron co-sputtering technology with hydrogen in Ar atmosphere. Compared to the MnxGe1−x films without hydrogen, the MnxGe1−x:H films with hydrogen show higher concentration of hole carriers, larger conductivity, and higher saturation magnetization. Moreover, it was found that the anomalous Hall resistivity is proportional to the perpendicular magnetization. These electrical and magnetic properties indicate that the ferromagnetism of the MnxGe1−x:H films is intrinsic ferromagnetism mediated by the spin-polarized hole carriers.

Amorphous MnxGe1−x:H ferromagnetic semiconductor films prepared in mixed Ar with 20% H2 by magnetron co-sputtering show global ferromagnetism with positive coercivity at low temperatures. With increasing temperature, the coercivity of MnxGe1−x:H films first changes from positive to negative, and then back to positive again, which was not found in the corresponding MnxGe1−x and other ferromagnetic semiconductors before. For Mn0.4Ge0.6:H film, the inverted Hall loop is also observed at 30 K, which is consistent with the negative coercivity. The negative coercivity is explained by the antiferromagnetic exchange coupling between the H-rich ferromagnetic regions separated by the H-poor non-ferromagnetic spacers. Hydrogenation is a useful method to tune the magnetic properties of MnxGe1−x films for the application in spintronics.

A series of high quality single crystalline epitaxial Zn0.95Co0.05O thin films is prepared by molecular beam epitaxy. Superparamagnetism and ferromagnetism are observed when the donor density is manipulated in a range of 1018 cm−3−1020 cm−3 by changing the oxygen partial pressure during film growth. The conduction shows variable range hopping at low temperature and thermal activation conduction at high temperature. The ferromagnetism can be maintained up to room temperature. However, the anomalous Hall effect is observed only at low temperature and disappears above 160 K. This phenomenon can be attributed to the local ferromagnetism and the decreased optimal hopping distance at high temperatures.

Fe𝑥Ge1−𝑥/Ge amorphous heterojunction diodes with p-Fe𝑥Ge1−𝑥 ferromagnetic semiconductor layers are grown on single-crystal Ge substrates of p-type, n-type and intrinsic semiconductors, respectively. The 𝐼-𝑉 curves of p-Fe0.4Ge0.6/p-Ge diodes only show slight changes with temperature or with magnetic field. For the p-Fe0.4Ge0.6/n-Ge diode, good rectification is maintained at room temperature. More interestingly, the 𝐼-𝑉 curve of the p-Fe0.4Ge0.6/i-Ge diode can be tuned by the magnetic field, indicating a large positive magnetoresistance. The resistances of the junctions decrease with the increasing temperature, suggesting a typical semiconductor transport behavior. The origin of the positive magnetoresistance is discussed based on the effect of the electric and magnetic field on the energy band structures of the interface.