3d-transition-metal-doped ZnO films (n-type Zn1−xMxO (x=005–025): M=Co, Mn, Cr, Ni) are formed on sapphire substrates using a pulsed-laser deposition technique, and their magnetic and electric properties are examined The Co-doped ZnO films showed the maximum solubility limit Some of the Co-doped ZnO films exhibit ferromagnetic behaviors with the Curie temperature higher than room temperature The magnetic properties of Co-doped ZnO films depend on the concentration of Co ions and carriers

Magnetic and electric properties of transition-metal-doped ZnO films

We report on the epitaxial growth of a group-IV ferromagnetic semiconductor, Mn(x)Ge(1-x), in which the Curie temperature is found to increase linearly with manganese (Mn) concentration from 25 to 116 kelvin. The p-type semiconducting character and hole-mediated exchange permit control of ferromagnetic order through application of a +/-0.5-volt gate voltage, a value compatible with present microelectronic technology. Total-energy calculations within density-functional theory show that the magnetically ordered phase arises from a long-range ferromagnetic interaction that dominates a short-range antiferromagnetic interaction. Calculated spin interactions and percolation theory predict transition temperatures larger than measured, consistent with the observed suppression of magnetically active Mn atoms and hole concentration.

http://science.sciencemag.org/content/sci/295/5555/651.full.pdf

A Group-IV Ferromagnetic Semiconductor: MnxGe1−x

Recent advances in the theory and experimental realization of ferromagnetic semiconductors give hope that a new generation of microelectronic devices based on the spin degree of freedom of the electron can be developed. This review focuses primarily on promising candidate materials (such as GaN, GaP and ZnO) in which there is already a technology base and a fairly good understanding of the basic electrical and optical properties. The introduction of Mn into these and other materials under the right conditions is found to produce ferromagnetism near or above room temperature. There are a number of other potential dopant ions that could be employed (such as Fe, Ni, Co, Cr) as suggested by theory [see, for example, Sato and Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 39, L555 (2000)]. Growth of these ferromagnetic materials by thin film techniques, such as molecular beam epitaxy or pulsed laser deposition, provides excellent control of the dopant concentration and the ability to grow single-phase layers. T...

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Wide band gap ferromagnetic semiconductors and oxides

The current status and prospects of research on ferromagnetism in semiconductors are reviewed The question of the origin of ferromagnetism in europium chalcogenides, chromium spinels and, particularly, in diluted magnetic semiconductors is addressed The nature of electronic states derived from 3d of magnetic impurities is discussed in some details Results of a quantitative comparison between experimental and theoretical results, notably for Mn-based III-V and II-VI compounds, are presented This comparison demonstrates that the current theory of the exchange interactions mediated by holes in the valence band describes correctly the values of Curie temperatures T_C magnetic anisotropy, domain structure, and magnetic circular dichroism On this basis, chemical trends are examined and show to lead to the prediction of semiconductor systems with T_C that may exceed room temperature, an expectation that are being confirmed by recent findings Results for materials containing magnetic ions other than Mn are also presented emphasizing that the double exchange involving hoping through d states may operate in those systems

Ferromagnetic semiconductors

Spintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spindependent tunneling, as well as spin relaxation and spin dynamics The most fundamental spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field

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Semiconductor Spintronics

High concentration of Mn atoms has been incorporated in the surface region of II-IV-V2 type chalcopyrite semiconductor CdGeP2 Photoluminescence spectrum at 20 K shows a peak around 32 eV, suggesting that the incorporation of Mn introduces an energy gap much higher than that of the host semiconductor (Eg=183 eV) Prominent magnetic hysteresis loops with coercivity of 05 kOe has been observed at room temperature Magnetic force microscope (MFM) measurements reveal a stripe-shaped domain pattern on the top surface Magneto-optical Kerr ellipticity spectrum measured at room temperature show a prominent peak at 17 eV and a broad tail up to 35 eV We tentatively attribute the ferromagnetism to the double exchange interaction between Mn2+ and Mn3+ states due to the structural feature of II-IV-V2 type chalcopyrite compounds

https://iopscience.iop.org/article/10.1143/JJAP.39.L949/pdf

Room Temperature Ferromagnetism in Novel Diluted Magnetic Semiconductor Cd1¡xMnxGeP2

Magnetic and magneto-optical properties were measured at room temperature in the Mn-diffused surface layer of a CdGeP2 single crystal. The magnetization curve measured using VSM clearly shows a ferromagnetic hysteresis loop with Hc=0.4 kOe superposed on the diamagnetic component. The ferromagnetic Curie temperature was determined as 320 K from the magnetization vs. temperature curve. The magneto-optical Kerr effect was measured between 1.2 and 4 eV. The peak Kerr ellipticity of 0.14 deg appeared around 1.75 eV.

/pdf/magnetic-and-magneto-optical-properties-of-a-novel-31a04kab21.pdf

Magnetic and Magneto-Optical Properties of a Novel Ferromagnetic Semiconductor CdGeP2:Mn

Ferromagnetic EuO films were epitaxially grown on MgO substrate The Curie temperature Tc of the obtained film was 69K Spectra of magneto-optical polar Kerr rotation and Kerr ellipticity were measured from the substrate side of the MgO/EuO/Ag structure using the photoelastic modulator technique for photon energies between 12 and 4 eV under the magnetic field of 1T Huge magneto-optical effect was obtained A few spectral structures were observed for photon energies between 12 and 26eV, which undergo strong temperature dependence

Yoichi Hasegawa

Papers

Room Temperature Ferromagnetism in Novel Diluted Magnetic Semiconductor Cd1¡xMnxGeP2

Magnetic and Magneto-Optical Properties of a Novel Ferromagnetic Semiconductor CdGeP2:Mn

Temperature Dependence of Magneto-Optical Spectra in EuO Epitaxial Films