Theory of ferromagnetic semiconductors

Abstract

Based upon ab initio electronic structure calculations by the Korringa -Kohn -Rostoker coherentpotential approximation (KKR-CPA) method within the local-density approximation (LDA), we propose a unified physical picture of magnetism and an accurate calculation method of Curie temperature (T C ) in dilute magnetic semiconductors (DMSs) in II -VI and III -V compound semiconductors. We also propose the unified physical picture of magnetism in the DMS, where ferromagnetic Zener's double-exchange mechanism (or Zener's p -d exchange mechanism) caused by the partially occupied impurity band and anti-ferromagnetic super-exchange mechanism (or ferromagnetic super-exchange mechanism) is competing to determine the magnetic states in the DMS. We propose that the three-dimensional 3D Dairisekiphase and one-dimensional 1D Konbu-phase caused by spinodal nano-decomposition are responsible for high-T C phase in the inhomogeneous system. We propose the new methodology to go beyond LDA to describe the highly correlated electron system by taking into account the self-interaction correction (SIC) to the LDA. the quantal phase (or Berry's phase) and nano-dynamics of spin, charge and atoms in the nano-structures of semiconductors.In order to boost the research on semiconductor nano-spintronics dramatically, we need to realize the high-temperature ferromagnetism (a few times higher-T C than the room temperature) with dilute magnetic semiconductor (DMS) nano-structures for the application of high-density (Tera-bit density per inch 2 ), high-speed (Tera-Hz switching), and low-power consumption (non-volatile memory) electronics. In spintronics application, magnetic properties may be carried by conventional metallic ferromagnets (Fe, Co and Ni) or dilute magnetic semiconductors (DMS) such as (Ga,Mn)As or (In,Mn)Sb. These materials are metallic or bad-metallic systems, therefore, we cannot control the magnetic properties by an electric field through the application of gate voltage. We need to develop the new control method of spin by electric field in semiconductors, carrier controlled ferromagnetism, spin injection into nanostructures, spin correction, spin manipulations, and spin detection, if we seriously want to develop a new class of electronics by semiconductor nano-spintronics to go beyond the silicon CMOS nanotechnology. To do so, self-controlled growth-positioning by the seeding, self-assembled and self-organized fabrication method of nano-scale-size ferromagnets (nano-magnets) in semiconductor matrix is absolutely necessary. This is the only method to control the spin by electric field in order to realize the new class of electronics by controlling the spin and charge degrees of freedom of electrons in the semiconductors. These new fabrication method of nano-magnets in semiconductor matrix permit the real application of semiconductor nano-spintronics [1], such as colossal or giant magneto-resistant memory, high sensitive field sensors, spin transistors, reconfigurable logic and quantum information and communication processing. In t...

Magnetooptical Properties of (Ga,Fe)N Layers

“…Since Fe nanocrystals are located predominantly near the film surface, this result confirms previous findings [3] that the ferromagnetic signal of the films comes from the nanocrystals.…”

“…Doping of a semiconductor with transition metal ions above the solubility limit results in the formation of nanometer size, metal ion-rich regions differing either chemically or crystallographically from a host matrix [2]. Such decomposed systems might offer several novel functionalities [2,3].…”

Advances in methods to obtain and characterise room temperature magnetic ZnO

“…[1][2][3][4][5][6] However, there is now consent that the origin of the magnetically ordered state in diluted oxide semiconductors is related to lattice defects and/or added ions, which are not necessarily magnetic, a phenomenon called defect-induced magnetism. [7][8][9][10][11][12][13] Nevertheless, in spite of the large number of experimental studies, there is no simple method to introduce systematically the required defect concentration in the corresponding lattice sites. Moreover, low resistivity and magnetic p-type oxides, necessary for further implementation in electronic devices, remain an unresolved goal partially because of the formation of oppositely charged defects, which pin the Fermi level.…”

Origin and control of ferromagnetism in dilute magnetic semiconductors and oxides (invited)

“…50,51 These two cases correspond to precipitation of other phases and spinodal decomposition, respectively. As emphasized in recent reviews, 49,52,53,54 the film decomposition into nanoregions with low and high concentrations of magnetic ions constitutes a generic property of many DMS and DMO, occurring if the mean density of the magnetic constituent exceeds the solubility limit at given growth or thermal processing conditions. Importantly, the host can stabilize magnetic nanostructures in a new crystallographic and/or chemical form, not as yet listed in materials compendia.…”