# Unexpected Ferromagnetism--A Review
## 4 Applications and Future Trends
Another example presented in [122] is the device based on an all-oxide tri-layer FM-insulator-FM Zn\({}_{0.94}\)Co\({}_{0.06}\)O (25 nm)/MgO (4 nm)/Zn\({}_{0.94}\)Co\({}_{0.06}\)O (50 nm), which showed a TMR ratio of 46.8% at 2T magnetic field but at the very low temperature of only 2 K. The value of the V\({}_{1/2}\)--the bias voltage where the TMR ratio is half of the zero-bias value observed--was very high (10 V), which encouraged the authors to see a potential application in MRM (magnetoresistive random access memory) devices or in reading heads for hard disks--applications requiring a high voltage bias [122]. A similar all-oxidic device was presented in [123], where all three layers contain epitaxially grown zinc oxide: Zn\({}_{0.94}\)Co\({}_{0.06}\)O (50 nm)/ZnO (4 nm)/Zn\({}_{0.94}\)Co\({}_{0.06}\)O (25 nm). The researchers found a TMR positive ratio of 20.8% at 4 K that can exist (while much diminished) even at room temperature, whereby the TMR ratio was 0.35% at 2T due to a better crystallinity of both barrier and barrier-electrode interfaces, accompanied by a reduced bias-dependence TMR, which is promising for the Gb-scale MRAM [123]. For reliable spintronic devices, a major problem encountered was the efficient \"transfer of the spin-polarized carriers from a magnetic contact into a nanomagnetic semiconductor\", and one method to achieve this goal was to use--in the ambient conditions--a polarized laser light (optical pumping) [116]. However, for the electronic device integration, an electrical spin injection approach will be required [116]. Unfortunately, it is very difficult to obtain a good spin injection efficiency in the case of the interface between a DMO and semiconductor (the source and the channel), coupled with an efficient spin detection at the chain-drain interface, all these being required for performant spin-field emission transistors [116]. Another direction of applications of DMS and DMO is the potential to influence the magnetization not by an external magnetic field but by using an electrical field, which can be of great importance for the field of spintronics for device applications. As was demonstrated for the first time in [124] for the case of the Mn-doped indium arsenide thin-film magnetic semiconductor using an insulating-gate field-effect transistor. In addition, in an Mn-doped gallium arsenide [125], where it was concluded that the control of carriers (holes) concentration and of magnetic anisotropy was achieved via applied electric field on a metal-insulator-semiconductor device, which allowed for the manipulation of the magnetization direction, opening the path for non-volatile devices that do not need the intervention \"of a magnetic field, spin current, or mechanical stress\". A drawback of these materials is their Curie temperatures, which are usually low (below 190 K) [116]. However, another report [126] presented an epitaxial PbZr\({}_{0.2}\)Ti\({}_{0.8}\)O\({}_{3}\)/Co:TiO\({}_{2}\)/SrRuO\({}_{3}\) heterostructure grown on (001) LaAlO\({}_{3}\) that allows reversible modulation of the magnetization at room temperature (that imply both saturation magnetization and coercive field), possibly due to reorganization of the vacancy defects under the electric field influence.