Presence Of Magnetic Ions Research Articles

Multifaceted investigations of co-precipitated Ni-doped ZnO nanoparticles: Systematic study on structural integrity, optical interplay and photocatalytic performances

The present study demonstrates the successful synthesis of ZnO and nickel doped ZnO NPs by co-precipitation method. XRD analysis, confirms hexagonal wurtzite structure. The crystallite size increased from 31 to 45 nm with increasing Ni ions and a reduction in the unit cell volume, owing to the smaller ionic radius of Ni2+ compared to Zn2+. PL spectra were observed for pristine ZnO, associated with near band edge emission band, arising from the recombination of free excitons. Due to the splitting of orbitals caused by the presence of magnetic ions, the optical bandgap is found to be decreasing whereas an increase in the occupancy of 3d electrons. The absorption band observed corresponds to the stretching mode below 450 cm−1. A distinctive peak at around 436 cm−1 was identified in the Raman spectra, indicating the high-frequency branch E2 mode in ZnO. Ni-doped (Zn0·91Ni0·09O) NPs achieve about 80 % photodegradation of MEG dye.

Spin polarization of exciton-polariton condensate in a photonic synthetic effective magnetic field

The authors investigate here the spin polarization of localized exciton-polariton condensates in CdTe-based microcavities doped with magnetic ions. They demonstrate that an effective magnetic field originating from the photonic potential landscape leads to the formation of elliptically polarized condensate. The degree of spin polarization of the condensate depends on the excitation power and polarization of the laser. Based on the magnetic field behavior of the condensate in the presence of magnetic ions, they estimate the polariton-polariton interaction strength in a CdTe system.

Muon Spectroscopy for Investigating Diffusion in Energy Storage Materials

We review recent applications of positive muon spin relaxation (μSR) spectroscopy as an active probe of ion diffusion in energy storage materials. μSR spectroscopy allows the study of ionic diffusion in solid-state materials on a time scale between 10−5 and 10−8 s where most long-range and consecutive short-range jumps of ions between interstitial sites occur. μSR also allows one to probe and model ionic diffusion in materials that contain magnetic ions, since both electronic and nuclear contributions to the muon depolarization can be separated, making μSR an excellent technique for the microscopic study of the ionic motions in crystalline materials. We highlight a series of battery materials for which μSR has provided insight into intrinsic ionic conduction and magnetic properties without interference of external factors, such as the presence of magnetic ions, macroscopic particle morphologies, or elaborate measurement setups.

Charge Transfer, Band‐Like Transport, and Magnetic Ions at F16CoPc/Rubrene Interfaces

Organic semiconductors offer an unprecedented flexibility to control the electronic state of interfacial electronic systems. Here we present a first step in realizing organic charge transfer interfaces that combine both a large electrical conductivity and the presence of magnetic ions. We have performed a detailed investigation of F16CoPc/rubrene interface by means of temperature dependent charge transport measurements, Hall effect, scanning Kelvin probe microscopy and photoelectron spectroscopy. Our finding is that the charge transfer leads to significantly enhanced electrical conductivity and the band-like transport. We have determined the density, mobility and nature of charge carriers in the system (holes in rubrene). We have also found that the amount of charge transfer in F16CoPc/rubrene is high enough to cause the band-like transport in rubrene crystals at the interface. Finally, our XPS and UPS measurements have shown that the charge transfer in F16CoPc/rubrene involves electronic orbitals centered on the magnetic Co ions of the phthalocyanine molecules causing a change in their spin. Thus, F16CoPc/rubrene is the first organic interface where the charge transfer responsible for the interfacial conductivity fully involves the metal Co core of the phthalocyanine molecules, providing a link between charge transport and magnetic properties.

Study of the structural, electric and magnetic properties of Mn-doped Bi2Te3 single crystals

Breaking the time reversal symmetry of a topological insulator, for example by the presence of magnetic ions, is a prerequisite for spin-based electronic applications in the future. In this regard Mn-doped Bi2Te3 is a prototypical example that merits a systematic investigation of its magnetic properties. Unfortunately, Mn doping is challenging in many host materials—resulting in structural or chemical inhomogeneities affecting the magnetic properties. Here, we present a systematic study of the structural, magnetic and magnetotransport properties of Mn-doped Bi2Te3 single crystals using complimentary experimental techniques. These materials exhibit a ferromagnetic phase that is very sensitive to the structural details, with TC varying between 9 and 13 K (bulk values) and a saturation moment that reaches 4.4(5) μB per Mn in the ordered phase. Muon spin rotation suggests that the magnetism is homogeneous throughout the sample. Furthermore, torque measurements in fields up to 33 T reveal an easy axis magnetic anisotropy perpendicular to the ab-plane. The electrical transport data show an anomaly around TC that is easily suppressed by an applied magnetic field, and also anisotropic behavior due to the spin-dependent scattering in relation to the alignment of the Mn magnetic moment. Hall measurements on different crystals established that these systems are n-doped with carrier concentrations of ∼ 0.5–3.0 × 1020 cm−3. X-ray magnetic circular dichroism (XMCD) at the Mn L2,3 edge at 1.8 K reveals a large spin magnetic moment of 4.3(3) μB/Mn, and a small orbital magnetic moment of 0.18(2) μB/Mn. The results also indicate a ground state of mixed d4–d5–d6 character of a localized electronic nature, similar to the diluted ferromagnetic semiconductor Ga1−xMnxAs. XMCD measurements in a field of 6 T give a transition point at T ≈ 16 K, which is ascribed to short range magnetic order induced by the magnetic field. In the ferromagnetic state the easy direction of magnetization is along the c-axis, in agreement with bulk magnetization measurements. This could lead to gap opening at the Dirac point, providing a means to control the surface electric transport, which is of great importance for applications.

Dirac-fermion-mediated ferromagnetism in a topological insulator

Topological insulators are a newly discovered class of materials in which helical conducting modes exist on the surface of a bulk insulator1,2,3,4,5,6. Recently, theoretical works have shown that breaking gauge symmetry7 or time-reversal symmetry8 in these materials produces exotic states that, if realized, represent substantial steps towards realizing new magnetoelectric effects9,10 and tools useful for quantum computing11. Here we demonstrate the latter symmetry breaking in the form of ferromagnetism arising from the interaction between magnetic impurities and the Dirac fermions12,13. Using devices based on cleaved single crystals of Mn-doped Bi2Te3−ySey, the application of both solid-dielectric and ionic-liquid gating allows us to measure the transport response of the surface states within the bulk bandgap in the presence of magnetic ions. By tracking the anomalous Hall effect we find that the surface modes support robust ferromagnetism as well as magnetoconductance that is consistent with enhanced one-dimensional edge-state transport on the magnetic domain wall. Observation of this evidence for quantum transport phenomena demonstrates the accessibility of these exotics states in devices and may serve to focus the wide range of proposed methods for experimentally realizing the quantum anomalous Hall effect8,10 and states required for quantum computing14,15.

Structure, transport and magnetic properties in La2xSr2−2xCo2xRu2−2xO6

The perovskite solid solutions of the type La2xSr2−2xCo2xRu2−2xO6 with 0.25≤x≤0.75 have been investigated for their structural, magnetic and transport properties. All the compounds crystallize in double perovskite structure. The magnetization measurements indicate a complex magnetic ground state with strong competition between ferromagnetic and antiferromagnetic interactions. Resistivity of the compounds is in confirmation with hopping conduction behaviour though differences are noted especially for x=0.4 and 0.6. Most importantly, low field (50Oe) magnetization measurements display negative magnetization during the zero field cooled cycle. X-ray photoelectron spectroscopy measurements indicate the presence of Co2+/Co3+ and Ru4+/Ru5+ redox couples in all compositions except x=0.5. Presence of magnetic ions like Ru4+ and Co3+ gives rise to additional ferromagnetic (Ru-rich) and antiferromagnetic sublattices and also explains the observed negative magnetization.

Magnetic resonance imaging of brain iron

The development of effective staining and other tissue analysis techniques has long provided pathologists with a means of studying [1–4] and quantifying [5] the regional distribution of the non-heme iron stored in the brain. However, the nature of these techniques precluded premortem studies. Soon after the introduction of magnetic resonance (MR) imaging in the 1980s, it was recognized that some of the MR contrast present in brain images correlated closely with the previously established patterns of brain iron deposition [6]. The initial studies were performed using 1.5 tesla (T) magnets but it was quickly noted that this contrast increased rapidly with the use of higher field strength magnets [7–9]. In the early 1990s, only a handful of whole-body magnets operating at field strengths above 1.5 T were in use, and these were confined to research applications. However, fully featured clinical scanners operating at 3 T are now coming into widespread use, and whole-body research systems operating at 7 and 8 T are available at some research centers. As a result, the study of iron-dependent contrast at high magnetic field strengths is now much more feasible than was previously the case. The MR signal arises from mobile protons in the tissues. In brain, these protons are almost entirely present in the solvent water molecules as H2O. The image contrast arises from variations among brain regions of the density of solvent water and the longitudinal (T1) and transverse (T2) relaxation times of the associated protons [10]. Generally, regions with short values of T1 appear bright on T1-weighted images and regions of short T2 appear dark on T2-weighted images. The presence of magnetic ions can alter T1 and T2 and thereby the tissue contrast [11]. Many metallic ions essential to brain function (sodium, potassium, calcium, magnesium, and zinc) are nonmagnetic and have no impact on MR images. However, ions of the transition group (e.g., iron, manganese, and copper), and of the rare earth group (e.g., gadolinium and dysprosium) exhibit nonzero magnetic moments in many compounds and do have the potential of affecting MR contrast.

Excitonic dephasing in semimagnetic semiconductors

The presence of magnetic ions in a dilute semiconductor quantum well is shown to decrease dramatically the low-temperature excitonic dephasing time measured by transient four-wave mixing. The decrease is associated with the magnetic nature of the material. Surprisingly, the application of a magnetic field does not significantly change the dephasing time, which indicates that there must exist a fast dephasing mechanism in addition to the spin–spin interactions responsible for magnetic polaron formation.