A MgO tunnel barrier is sandwiched between semiconductor material on one side and a ferri- and/or ferromagnetic material on the other side to form a spintronic element. The semiconductor material may include GaAs, for example. The spintronic element may be used as a spin injection device by injecting charge carriers from the magnetic material into the MgO tunnel barrier and then into the semiconductor. Similarly, the spintronic element may be used as a detector or analyzer of spin-polarized charge carriers by flowing charge carriers from the surface of the semiconducting layer through the MgO tunnel barrier and into the (ferri- or ferro-) magnetic material, which then acts as a detector. The MgO tunnel barrier is preferably formed by forming a Mg layer on an underlayer (e.g., a ferromagnetic layer), and then directing additional Mg, in the presence of oxygen, towards the underlayer.