Ferromagnetism In Dilute Magnetic Semiconductors Research Articles

High-TC Ferromagnetic Semiconductors: Fake or Fact?

The long lasting interest in diluted magnetic semiconductors (DMS) relies on the combination of fundamental science and the potential for spintronics applications. Despite the large body of experimental and theoretical studies carried out in the past decades, there are ongoing controversies about high-TC ferromagnetic DMS. This paper summarizes the results of the few investigations performed by inelastic neutron scattering, which provides key information for some of the open questions. Emphasis is led on a complete study of the compound MnxGa1 – xN, as well as on novel DMS materials for which the spin injection is decoupled from carrier doping.

Magnetic phase tuning of diluted Fe-doped CuO nanoparticles through annealing temperature as characterized by first-order reversal curve analysis

Abstract Diluted magnetic semiconductors (DMSs) exhibit room temperature ferromagnetic behavior and have recently been used in a broad range of applications including spintronic devices. Here, we present a simple co-precipitation method to synthesize pure CuO and diluted Cu1−xFexO (x = 0.05 and 0.1) nanoparticles (NPs) with different annealing temperatures (Ta) ranging between 500 °C and 900 °C, achieving ferromagnetic DMSs with a monoclinic structure at room temperature. The mean NP size, evaluated using a field-emission scanning electron microscope, was found to increase with increasing Ta. A red shift was observed in UV–visible spectra and indicated the successful substitution of Fe ions in the CuO NPs, confirming the absence of impurity phases in the resulting structures. Investigating magnetic properties by hysteresis loop measurements, maximum saturation magnetization and coercive field values were obtained to be 4.8 emu/g and 325 Oe, respectively, for 10% Fe-doped CuO NPs at Ta = 900 °C. First-order reversal curve analysis was used to study detailed magnetic characteristics of the NPs. While a soft magnetic phase with superparamagnetic fractions ranging from approximately 41% to 53% dominated magnetic behavior at Ta = 700 °C, a strong hard phase determined the average magnetic properties of Fe-doped CuO NPs with nanocrystalline structure at Ta = 900 °C.

Review on Available Theoretical Models for Room Temperature Ferromagnetism in Dilute Magnetic Semiconductors

Review on Available Theoretical Models for Room Temperature Ferromagnetism in Dilute Magnetic Semiconductors

Photoelectric properties of Ag and Cr co-doped LiZnP new diluted magnetic semiconductors

Spintronic devices utilize the electron charge and spin degree of freedom to achieve novel quantum functionalities. Diluted magnetic semiconductors (DMS) constitute an important category of spintronic materials that have the potential to be successfully incorporated into the existing semiconductor industry. The prototypical DMS (Ga,Mn) As, discovered in the 1990s, accomplishes spin and charge doping simultaneously through the heterovalent substitution of the magnetic ion Mn2+ for Ga3+. Two challenges have presented themselves in this material. First, the heterovalent nature of this integrated spin/charge doping results in severely limited chemical solubility in (Ga,Mn) As, restricting specimen fabrication to metastable thin films by molecular beam epitaxy; second, the simultaneous spin and charge doping precludes the possibility of individually tuning the spin and charge degree of freedom. A new type of ferromagnetic DMS based on I-Ⅱ-V group can overcome both of these challenges. Li(Zn,Mn) As utilizes excess Li concentration to introduce hole carriers, while independently making the isovalent substitution of Mn2+ for Zn2+ in order to achieve local spin doping. With no heterovalent substitution to restrict chemical solubility, bulk samples of Li(Zn,Mn) As are successfully fabricated. However, one drawback of Li(Zn,Mn) As is its use of the toxic element As. The isostructural direct-gap semiconductor LiZnP also undergoes a ferromagnetic transition upon Mn doping, and its bulk magnetic properties are very similar to those of LiZnAs. In this paper, the geometric structure of pure LiZnP, Ag doped, Cr doped, and Ag-Cr co-doped LiZnP new diluted magnetic semiconductor are optimized by using the first-principles plane wave ultra-soft pseudo-potential technology based on the density function theory. Then we calculate the electronic structure, magnetism, formation energy, differential charge density, and optical properties of the doped systems. The results show that the material is a paramagnetic metal after single doping of the nonmagnetic element Ag. When magnetic element Cr is doped with LiZnP, sp-d orbital hybridization makes the peak of density of state nearly EF-split, leading the system to become metallic ferromagnetism. However, Ag-Cr co-doped LiZnP changes into half-metallic ferromagnetism, which is completely different from the single doping system. The band gap decreases slightly, and the electrical conductivity is enhanced. Meanwhile, the formation energy of the system becomes lower, the bond between atoms strengthens, and the stability of the unit cell becomes stronger. A comparison of the optical properties indicate that the imaginary part of dielectric function and the optical absorption spectrum both present new peaks in low energy region in the doped systems. Ag-Cr co-doped LiZnP has the highest dielectric peak. Meanwhile, the complex refractive index function changes obviously in a low energy region, and the absorption edge extends to the low energy direction. The system enhances the absorption of low-frequency electromagnetic waves.

Clustering and spin interactions in Fe-doped diamond

The origin of high Curie temperature ferromagnetism in dilute magnetic semiconductors and oxides has often been attributed to clustering and crystallographic phase separation of magnetic atoms, which may have a detrimental impact on the properties of the host material for target applications. We present Density Functional Theory calculations on the stability and magnetic interactions of embedded Fe+1 ions in diamond by considering various possible cluster configurations. We find that Fe ions have a strong tendency to form embedded clusters in diamond, with larger cluster sizes (n>3) suppressing the induced spin moment. Also, we find that the electronic structure of the stable embedded Fe+1 clusters is insulating, in contrast to homogeneous distribution, where a half metallic character with 100% spin polarisation at the Fermi level has previously been predicted. These results present important implications to the understanding of the properties of transition metal dopants in diamond, as well as in other dilute magnetic semiconductors where the effect of aggregation of dopants has generally been neglected.

Understanding lattice defects to influence ferromagnetic order of ZnO nanoparticles by Ni, Cu, Ce ions

Future spintronics technologies based on diluted magnetic semiconductors (DMS) will rely heavily on a sound understanding of the microscopic origins of ferromagnetism in such materials. It remains unclear, however, whether the ferromagnetism in DMS is intrinsic - a precondition for spintronics - or due to dopant clustering. For this, we include a simultaneous doping from transition metal (Ni, Cu) and rare earth (Ce) ions in ZnO nanoparticles that increase the antiferromagnetic ordering to achieve high-Tc ferromagnetism. Rietveld refinement of XRD patterns indicate that the dopant ions in ZnO had a wurtzite structure and the dopants, Ni2+, Cu2+, Ce3+ ions, are highly influenced the lattice constants to induce lattice defects. The Ni, Cu, Ce ions in ZnO have nanoparticles formation than nanorods was observed in pure sample. FTIR involve some organic groups to induce lattice defects and the metal-oxygen bonding of Zn, Ni, Cu, Ce and O atoms to confirm wurtzite structure. Raman analysis evaluates the crystalline quality, structural disorder and defects in ZnO lattice with doping. Photoluminescence spectra have strong near-band-edge emission and visible emission bands responsible for defects due to oxygen vacancies. The energy band gap is calculated using Tauc relation. Room temperature ferromagnetism has been described due to bound magnetic polarons formation with Ni2+, Cu2+, Ce3+ ions in ZnO via oxygen vacancies. The zero field and field cooling SQUID measurement confirm the strength of antiferromagnetism in ZnO. The field cooling magnetization is studied by Curie-Weiss law that include antiferromagnetic interactions up to low temperature. The XPS spectra have involve +3/+4 oxidation states of Ce ions to influence the observed ferromagnetism.

Understanding ferromagnetism in C-doped CdS: Monte Carlo simulation

Room-temperature ferromagnetism of diluted magnetic semiconductors (DMSs) doped with light elements has been extensively investigated for potential applications in spintronic devices. Indeed, the mechanism underlying ferromagnetism in DMSs of low concentrations has been studied from both theoretical and experimental perspectives. Theoretically, first-principles calculation and Monte Carlo (MC) simulation were combined together to study electronic and magnetic properties of DMSs. The Curie temperature of DMSs has been usually estimated from Monte Carlo simulation. In particular, MC simulations use both continuous and discrete spin models to describe the spin state in the ferromagnetic phase of DMSs. Nevertheless, which of the two models is the more appropriate is unclear. To clarify further this issue of ”continuous versus discrete” spin model in DMS materials, we have performed a large-scale MC simulation for C-doped CdS material. The discrete spin model sets the ferromagnetic phase transition below room-temperature whereas the continuous spin model sets this transition at rather low temperatures. The discrete spin model is found to describe more appropriately the spin state of C atoms in the C-doped CdS.

Electric-Field Control of Spin-Orbit Interaction for Low-Power Spintronics

Spintronics is regarded as a promising solution for resolving the major challenging issues related to the scaling of Si-based complementary metal–oxide–semiconductor (CMOS) technology as it offers the advantages of combing the spin and charge degrees of freedom. After decades of progress, the quintessence to achieve practical low-dissipation applications lies in the ability to manipulate magnetic states by electric field via several different physical mechanisms. Among them, the emergence of the spin-orbit coupling engineering has been shown to dramatically reduce energy dissipation and improve the performance as well as to multiply spintronic device possibilities and functionalities for a new generation of ultralow-power nonvolatile spintronic systems. This article provides a review of the current development including fundamental physics and experimental implementations of electric-field-controlled ferromagnetism in dilute magnetic semiconductors, voltage control of magnetic anisotropy, spin-orbit-torque-assisted magnetization switching, and antiferromagnetic (AFM) material-based spin-orbitronic systems. We provide an assessment in terms of scaling of energy, speed, and size. Finally, we offer an outlook of electric-field-controlled spintronic applications, particularly in view of their integration with CMOS to form hybrid spintronic circuits.

Ultrahigh Tunability of Room Temperature Electronic Transport and Ferromagnetism in Dilute Magnetic Semiconductor and PMN‐PT Single‐Crystal‐Based Field Effect Transistors via Electric Charge Mediation

Multiferroic heterostructures composed of complex oxide thin films and ferroelectric single crystals have aroused considerable interest due to the electrically switchable strain and charge elements of oxide films by the polarization reversal of ferroelectrics. Previous studies have demonstrated that the electric‐field‐control of physical properties of such heterostructures is exclusively due to the ferroelectric domain switching‐induced lattice strain effects. Here, the first successful integration of the hexagonal ZnO:Mn dilute magnetic semiconductor thin films with high performance (111)‐oriented perovskite Pb(Mg1/3Nb2/3)O3‐PbTiO3 (PMN‐PT) single crystals is reported, and unprecedented charge‐mediated electric‐field control of both electronic transport and ferromagnetism at room temperature for PMN‐PT single crystal‐based oxide heterostructures is realized. A significant carrier concentration‐tunability of resistance and magnetization by ≈400% and ≈257% is achieved at room temperature. The electric‐field controlled bistable resistance and ferromagnetism switching at room temperature via interfacial electric charge presents a potential strategy for designing prototype devices for information storage. The results also disclose that the relative importance of the strain effect and interfacial charge effect in oxide film/ferroelectric crystal heterostructures can be tuned by appropriately adjusting the charge carrier density of oxide films.

Coupling between magnetic and optical properties of GaN:TM (TM: V, Cr, Mn, Fe, Co, Ni): First-principle study with LDA-SIC approximation

Electronic structure, magnetic and optical properties of GaN:TM (TM: V, Cr, Mn, Fe, Co, Ni), based dilute magnetic semiconductors (DMS), are investigated using first-principles calculations. The energy difference between the ferromagnetic and disorder local moment states has been evaluated. Moreover, the optical absorption spectra obtained by ab-initio calculations confirm the ferromagnetic stability based on the charge state of magnetic impurities. Our results show that the ferromagnetic state is stable when TM introduce simultaneously magnetic moment and intrinsic carriers in (Ga, TM)N. Some studied ferromagnetic DMS exhibit half-metallic behavior, which is suitable for spintronics applications.

Ferromagnetic nanocomposites as spintronic materials with controlled magnetic structure

The physical properties of ferromagnetic dilute magnetic semiconductors and nanocomposites are considered in a wide range of temperatures from 5 to 300 K. The latter have several advantages as spintronic materials with a controlled magnetic structure for weak magnetic field sensors. A characteristic feature of ferromagnetic nanocomposites is the spin-dependent tunneling conductance, which is responsible for the negative and positive magnetoresistance. The magnetoresistive effects have a wide range of applications. In particular, materials with such effects may be used in the development of magnetoresistive memory devices, weak magnetic field sensors, medical diagnostic devices, and other items of electronic equipment.

Ferromagnetism in dilute magnetic semiconductors through defect engineering: N-doped BaTiO3

Based on spin-polarized density functional theory calculations, the induced magnetism of nitrogen-doped in the cubic BaTiO3 has been investigated. The Nsub has a magnetic moment of 1.00μB while the Nint has a magnetic moment of 0.94μB. The origin of the magnetism is induced by the oxygen and nitrogen 2p orbitals delocalized for Nsub. As for Nint, the ferromagnetism is reasonably described by the p–d exchange picture.

Magnetic behavior and clustering effects in Mn-doped boron nitride sheets

Ab initio calculations are performed in the framework of density functional theory on Mn-doped boron nitride sheets, which are candidates for two-dimensional diluted magnetic semiconductors (DMSs). Each type of substitution reveals a qualitatively different magnetic behavior encompassing ferromagnetic, anti-ferromagnetic and spin glass ordering. The ability of formation of these defects is also discussed. We analyze the dependence of the exchange couplings on the distance between impurities and the typical range and distribution are extracted. Multiple-impurity configurations are considered and the results are mapped on an Ising-type Hamiltonian with higher order exchange interactions, revealing deviations from the standard two-spin models. The percolation of interacting magnetic moments is discussed and the critical concentration is determined for the underlying transition from a ferromagnetic to a super-paramagnetic state. We conclude our study by providing the optimal conditions for doping in order to obtain a ferromagnetic DMS.

Correlation of Nanoscale Structure and Magnetic Properties in Manganese Doped Germanium Dilute Magnetic Semiconductors

ABSTRACTSpintronic devices generally require the spin of carriers to be utilized in the storage or manipulation of data. One theoretical model for ferromagnetism in dilute magnetic semiconductors (DMS) results from the percolation of ferromagnetic regions around dilute dopants such as Mn atoms in III-V or group IV materials through the interaction of Mn atoms with carriers. Our work employed Mn implantation in Ge with subsequent rapid thermal annealing or TEM in-situ annealing to study the correlation between structure and magnetic properties. The magnetic properties of 300-350 ºC implanted Ge:Mn (which produced crystalline Ge films) varied significantly with implantation dose and annealing condition due to precipitation and transformation of different MnxGe1-x secondary phases. It was found that Mn substitution of Ge and MnxGe1-x secondary phases can both result in ferromagnetic properties. By combining TEM in-situ annealing and ex-situ magnetic characterization, we have demonstrated detailed correlation of magnetic properties with nanoscale structures in Mn implanted Ge DMS materials.

From Nanoelectronics to Nano-Spintronics

Today's electronics uses electron charge as a state variable for logic and computing operation, which is often represented as voltage or current. In this representation of state variable, carriers in electronic devices behave independently even to a few and single electron cases. As the scaling continues to reduce the physical feature size and to increase the functional throughput, two most outstanding limitations and major challenges, among others, are power dissipation and variability as identified by ITRS. This paper presents the expose, in that collective phenomena, e.g., spintronics using appropriate order parameters of magnetic moment as a state variable may be considered favorably for a new room-temperature information processing paradigm. A comparison between electronics and spintronics in terms of variability, quantum and thermal fluctuations will be presented. It shows that the benefits of the scalability to smaller sizes in the case of spintronics (nanomagnetics) include a much reduced variability problem as compared with today's electronics. In addition, another advantage of using nanomagnets is the possibility of constructing nonvolatile logics, which allow for immense power savings during system standby. However, most of devices with magnetic moment usually use current to drive the devices and consequently, power dissipation is a major issue. We will discuss approaches of using electric-field control of ferromagnetism in dilute magnetic semiconductor (DMS) and metallic ferromagnetic materials. With the DMSs, carrier-mediated transition from paramagnetic to ferromagnetic phases make possible to have devices work very much like field effect transistor, plus the non-volatility afforded by ferromagnetism. Then we will describe new possibilities of the use of electric field for metallic materials and devices: Spin wave devices with multiferroics materials. We will also further describe a potential new method of electric field control of metallic ferromagnetism via field effect of the Thomas Fermi surface layer.

First-principles theory of dilute magnetic semiconductors

This review summarizes recent first-principles investigations of the electronic structure and magnetism of dilute magnetic semiconductors (DMSs), which are interesting for applications in spintronics. Details of the electronic structure of transition-metal-doped III-V and II-VI semiconductors are described, especially how the electronic structure couples to the magnetic properties of an impurity. In addition, the underlying mechanism of the ferromagnetism in DMSs is investigated from the electronic structure point of view in order to establish a unified picture that explains the chemical trend of the magnetism in DMSs. Recent efforts to fabricate high-${T}_{C}$ DMSs require accurate materials design and reliable ${T}_{C}$ predictions for the DMSs. In this connection, a hybrid method (ab initio calculations of effective exchange interactions coupled to Monte Carlo simulations for the thermal properties) is discussed as a practical method for calculating the Curie temperature of DMSs. The calculated ordering temperatures for various DMS systems are discussed, and the usefulness of the method is demonstrated. Moreover, in order to include all the complexity in the fabrication process of DMSs into advanced materials design, spinodal decomposition in DMSs is simulated and we try to assess the effect of inhomogeneity in them. Finally, recent works on first-principles theory of transport properties of DMSs are reviewed. The discussion is mainly based on electronic structure theory within the local-density approximation to density-functional theory.

Magnetic Properties of Ni-doped ZnO Nanocombs by CVD Approach

The search for above room temperature ferromagnetism in dilute magnetic semiconductors has been intense in recent year. Arrays of perpendicular ferromagnetic nanowire/rods have recently attracted considerable interest for their potential use in many areas of advanced nanotechnology. We report a simple low-temperature chemical vapor deposition (CVD) to create self-assembled comb-like Ni-/undoped ZnO nanostructure arrays. The phases, compositions, and physical properties of the studied samples were analyzed by different techniques, including high-resolution X-ray diffraction/photoelectron spectroscopy/transmission electron microscopy, photoluminescence, and MPMS. In particular, the Ni-doped ZnO nanocombs (NCs) with ferromagnetic and superparamagnetic properties have been observed whereas undoped ZnO NCs disappear. The corresponding ferromagnetic source mechanism is discussed, in which defects such as O vacancies would play an important role.

Ferromagnetism in Dilute Magnetic Semiconductors through Defect Engineering: Li-Doped ZnO

We demonstrate, both theoretically and experimentally, that cation vacancy can be the origin of ferromagnetism in intrinsic dilute magnetic semiconductors. The vacancies can be controlled to tune the ferromagnetism. Using Li-doped ZnO as an example, we found that while Li itself is nonmagnetic, it generates holes in ZnO, and its presence reduces the formation energy of Zn vacancy, and thereby stabilizes the zinc vacancy. Room temperature ferromagnetism with p type conduction was observed in pulsed laser deposited ZnO:Li films with certain doping concentration and oxygen partial pressure.

Atom-Probe Tomographic Studies of Thin Films and Multilayers

AbstractThis article reviews investigations of the growth and reactions within thin metal and oxide films using atom-probe tomography. Included in this review are (1) studies of interfacial and growth reactions in magnetoresistive metallic, metal/oxide, and magnetic magnetostrictive multilayers; (2) comparison of selected portions of these results to simulated film growth using molecular dynamics; and (3) study of the origin of room-temperature ferromagnetism in dilute magnetic semiconductors. Information of this type is useful in order to understand the formation and thermal evolution of thin films (and to compare to theory and modeling) and, ultimately, to permit further optimization of devices based on thin films.

ChemInform Abstract: Origin and Control of Ferromagnetism in Dilute Magnetic Semiconductors and Oxides

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.