Based upon ab initio electronic structure calculations by the Korringa-Kohn-Rostoker coherent-potential 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.

Theory of ferromagnetic semiconductors

Theoretical methods have greatly influenced experiment in search of the elusive marriage between semiconductor electronics and magnetism, and the development of spintronics. The path has not always been a straight one, but realizing the limitations and strengths of theoretical approaches promises a straighter course.

https://physics.aps.org/articles/pdf/10.1103/Physics.3.53

The quest for dilute ferromagnetism in semiconductors: Guides and misguides by theory

Magnetism in systems that do not contain transition metal or rare earth ions was recently observed or predicted to exist in a wide variety of systems. We summarize both experimental and theoretical results obtained for ideal bulk II-V and II-IV compounds, molecular crystals containing O(2) or N(2) molecules as structural units, as well as for carbon-based materials such as graphite and graphene nanoribbons. Magnetism can be an intrinsic property of a perfect crystal, or it can be induced by non-magnetic dopants or defects. In the case of vacancies, spin polarization is local and results in their high spin states. The non-vanishing spin polarization is shown to originate in the strong spin polarization of the 2p shell of light atoms from the second row of the periodic table.

https://iopscience.iop.org/article/10.1088/0953-8984/22/7/073202/pdf

Magnetism of solids resulting from spin polarization of p orbitals

We have studied structural, electronic, and magnetic properties of the graphene-like ZnO monolayer doped with nonmetal species using the first-principles calculations. Particular attention has been...

Tunable Magnetism in a Nonmetal-Substituted ZnO Monolayer: A First-Principles Study

This review presents the recent progress in computational materials design, experimental realization, and control methods of spinodal nanodecomposition under three- and two-dimensional crystal-growth conditions in spintronic materials, such as magnetically doped semiconductors. The computational description of nanodecomposition, performed by combining first-principles calculations with kinetic Monte Carlo simulations, is discussed together with extensive electron microscopy, synchrotron radiation, scanning probe, and ion beam methods that have been employed to visualize binodal and spinodal nanodecomposition (chemical phase separation) as well as nanoprecipitation (crystallographic phase separation) in a range of semiconductor compounds with a concentration of transition metal (TM) impurities beyond the solubility limit. The role of growth conditions, codoping by shallow impurities, kinetic barriers, and surface reactions in controlling the aggregation of magnetic cations is highlighted. According to theoretical simulations and experimental results the TM-rich regions appear in the form of either nanodots (the dairiseki phase) or nanocolumns (the konbu phase) buried in the host semiconductor. Particular attention is paid to Mn-doped group III arsenides and antimonides, TM-doped group III nitrides, Mn- and Fe-doped Ge, and Cr-doped group II chalcogenides, in which ferromagnetic features persisting up to above room temperature correlate with the presence of nanodecomposition and account for the application-relevant magneto-optical and magnetotransport properties of these compounds. Finally, it is pointed out that spinodal nanodecomposition can be viewed as a new class of bottom-up approach to nanofabrication.

Spinodal nanodecomposition in semiconductors doped with transition metals

We propose a new class of diluted magnetic semiconductors based on CaO without transition metal elements. The electronic structure and the magnetic properties of B-, C- or N-doped CaO are calculated by using the Korringa-Kohn-Rostoker method within the local spin density approximation. The substitutional and magnetic disorder is taken into account by the coherent potential approximation. It is found that B, C and N impurities show finite local magnetic moments in CaO at the oxygen-substitutional site. Moreover, these C- and N-doped CaO show the room-temperature ferromagnetism with half-metallic density of states.

https://iopscience.iop.org/article/10.1143/JJAP.43.L934/pdf

New Class of Diluted Ferromagnetic Semiconductors based on CaO without Transition Metal Elements

We propose materials design to fabricate a new class of diluted magnetic semiconductors (DMSs) based on MgO, SrO and BaO without magnetic elements. Replacing the oxygen atoms by other atoms such as C atoms leads to the induction of a deep-impurity band. These materials show ferromagnetic behaviour if the impurity-band width ( W ) and the electron-correlation energy ( U ) satisfy the conditions of a highly correlated electron system ( U > W ). Based on first-principles calculations, we demonstrate that these materials could satisfy Stoner's condition, and could be new candidates for transparent and half-metallic ferromagnetic DMSs without any magnetic elements.

Materials Design of Transparent and Half-Metallic Ferromagnets of MgO, SrO and BaO without Magnetic Elements

We propose materials design of ferromagnetic diamond without any transition metal elements based on first principles calculations. The electronic structure and the magnetic properties of impurities-doped diamond are calculated by using the Korringa-Kohn-Rostoker method within the local spin density approximation with taking into account disorder using coherent potential approximation. It is found that H atoms which are doped into tetrahedral interstitial sites show finite local magnetic moments. Moreover, the impurities-doped diamond show ferromagnetism with half-metallic density of states.

http://iopscience.iop.org/article/10.1143/JJAP.44.L51/pdf

Materials Design of Ferromagnetic Diamond

We propose a new route for ferromagnetic diluted magnetic semiconductors by controlling the impurity-band width (W) and the electron-correlation energy (U) in the partially occupied impurity band in the condition of highly correlated electron system (U>W). Based upon first-principles calculations of K2(S,Si) and K2(S,Ge), we demonstrate that transparent, half-metallic and room-temperature ferromagnetic DMS could be designed even without transition metal elements. The results show that it is possible to fabricate the room-temperature ferromagnets in K2(S,Si) and K2(S,Ge) around 8 at%-impurity concentration.

New Route to Fabricate Ferromagnetic Semiconductors without Transition Metal Elements

A single crystalline transparent ferromagnetic compound which transmits a light and also has high ferromagnetic characteristics, characterized in that it is a compound selected from the group of an alkaline earth chalcogenide, an alkali calcogenide, a I-VII Group compound, a II-VI Group compound, a III-V Group compound, a IV-VI2 Group compound, a IV-IV Group compound and a II-VII2 Group compound, and forms a solid solution with at least one element having an imperfect p electron shell as an outermost shell, such as B, C, N, O, F, Si and Ge, to thereby have a ferromagnetism transition temperature of room temperature or higher. Ferromagnetic characteristics of the above ferromagnetic compound are adjusted by controlling valence electrons through the adjustment of the concentration of the element having an imperfect p electron shell as an outermost shell, the addition of an acceptor and a donor, and the like.

Transparent ferromagnetic compound containing no magnetic impurity such as transition metal or rare earth metal and forming solid solution with element having imperfect shell, and method for adjusting ferromagnetic characteristics thereof

Kazuhide Kenmochi

Papers

New Class of Diluted Ferromagnetic Semiconductors based on CaO without Transition Metal Elements

Materials Design of Transparent and Half-Metallic Ferromagnets of MgO, SrO and BaO without Magnetic Elements

Materials Design of Ferromagnetic Diamond

New Route to Fabricate Ferromagnetic Semiconductors without Transition Metal Elements

Transparent ferromagnetic compound containing no magnetic impurity such as transition metal or rare earth metal and forming solid solution with element having imperfect shell, and method for adjusting ferromagnetic characteristics thereof