Ferromagnetic Metallic Behavior Research Articles

The structural, electronic and magnetic properties of [formula omitted] anti-perovskite

A comprehensive exploration of the structural, electronic, and magnetic attributes of anti-perovskite Fe3ZnC carbides was carried out using Density Functional Theory (DFT) and Monte Carlo Simulation (MCS). These anti-perovskite materials possess a unique structure where cation and anion positions are interchanged within the perovskite framework. Our study involves a comparative analysis of the electronic band structures and density of states (DOS) for Fe3ZnC, considering prior theoretical and experimental research. Understanding these anti-perovskite materials' band structures and DOS is pivotal for their effective utilization in magnetic sensors and magnetic refrigeration applications. Our results indicate that Fe3ZnC displays ferromagnetic metallic behavior, particularly when applying the Generalized Gradient Approximation (GGA). Notably, there is a significant overlap between the valence (VB) and conduction (CB) bands. Furthermore, MCS predicts a second-order ferromagnetic-to-paramagnetic transition in the anti-perovskite Fe3ZnC compound, characterized by a notably high Curie temperature. These insights advance our understanding of these materials, paving the way for their effective utilization in magnetic technologies.

Study of the correlation between the magnetic and electrical properties of the La0.6Sr0.4MnO3 compound.

In this work, we investigated the relationship between the electrical and magnetic properties of the superparamagnetic (SPM) La0.6Sr0.4MnO3 (S1C0) compound prepared by the sol-gel method. The (S1C0) sample displayed a ferromagnetic metallic (FMM) behavior at low temperatures and a paramagnetic semiconductor (PMSC) behavior at high temperatures. The FMM behavior was described by the Zener Double Exchange (ZDE) polynomial law containing the contributions of the electron-electron (e-e) interactions and the electron-magnon (e-m) scattering. The PMSC behavior was described by the Mott Variable Range Hopping (Mott-VRH) transport model. The semiconductor/metallic transition temperature has been approximated at the blocking temperature. The Thermal Coefficient of Resistivity (TCR), which exhibits a linear variation around ambient temperature, can be used as a calibration curve for thermometry. Thus, our sample can be considered as a good candidate for the detection of infrared radiation used in night vision bolometer technologies.

Study of Magnetoresistance Effect and Magnetic Properties of La<sub>0.67</sub>Sr<sub>0.33</sub>Mn<sub>1-<i>x</i></sub>Ni<i><sub>x</sub></i>O<sub>3</sub> (x = 0 and 0.2) Material Prepared by Sol-Gel Method

Mixed valence manganite materials have been studied due to their interesting physical properties such as their magnetoresistance (MR) effect. The change of Mn3+/Mn4+ ratio affects the possible bonds between anion and cation and their spin structure that may occur in the samples. The aim of this research is to study the change of magnetoresistance effect and magnetic properties of La0.67Sr0.33MnO3 (LSMO) by doping the Mn site with Ni ion. La0.67Sr0.33Mn1-xNixO3 samples were synthesized by using sol-gel method and characterized by using X-ray diffractometer (XRD) and Energy Dispersive X-ray spectroscopy (EDX) to confirm whether Ni has been doped successfully to the parental compound or not. XRD results showed that the samples have a single phase and Ni peak has been detected in the EDX result of Ni-doped LSMO. Resistivity and magnetic measurement showed that LSMO material has ferromagnetic metallic behavior, while x = 0.20 Ni-doped LSMO sample showed paramagnetic insulator behavior. The absolute value of the MR for un-doped sample is higher than the doped sample when the low field is applied, while under the influence of the high magnetic field, it become smaller than the doped sample.

The consequences of growth modes on the magnetotransport properties of La0.4Pr0.3Ca0.3MnO3/LAO films

The impact of pulse repetition rate and film thickness on the magnetic, magnetoresistance (MR) and anisotropic magnetoresistance (AMR) has been investigated for La0.4Pr0.3Ca0.3MnO3 thin films grown on LaAlO3 (LAO) substrates by pulsed laser deposition technique. Change in repetition rate led to a difference in growth modes and altered the magnetic and electrical properties (MR and AMR) of thin films. The XRD results show that in the films with the thickness of 100 nm, by increasing the pulse repetition rate from 2 to 7 Hz the strain level doesn’t change, while strain significantly increased at the repetition rate of 10Hz. Analysis of transport and magnetization measurements show that at 2 and 5 Hz deposited films, the ferromagnetic metallic behavior is dominant, while in the film deposited at 10 Hz the antiferromagnetic (AFM) insulating phase increased. Moreover, with increasing strain in the thinner films (40 nm), deposited at 2 Hz, AFM phase is strengthened. Exchange bias confirms the existence of a dead layer in 100 nm film deposited at 10 Hz and 40 nm film deposited at 2 Hz. In addition, high strain in thinner films led to an enhanced Jahn-Teller coupling, so the angular momentum and spin-orbital/lattice interactions are significantly increased, which led to a lower magnetoresistance in thinner films. These results suggest that the pulse repetition rate provides an additional degree of freedom to tune magnetic and electrical properties of manganite thin films prepared by pulsed laser deposition technique.

Peculiar Magnetic Properties in Doped and Edge Functionalized Silicene Nanoribbons

Motivated by the exceptional properties of graphene, other two-dimensional (2D) nanomaterials beyond graphene such as silicene have emerged with growing interest. Silicene is attractive for its exceptional characteristics and compatibility with silicon based nanoelectronics. It is believed that silicene may challenge graphene due to a longer spin-diffusion time, a longer spin coherence length, and a much larger spin-orbit coupling gap. Half-metallic materials and spin-gapless semiconductors (SGS) are highly desirable for spintronics because they provide 100% spin-polarized currents around their Fermi level. Spin filters and spin field effect transistors (FETs) are one of the potential applications of these types of materials. Silicene nanoribbon (SiNR) as an approach to opening a band gap in a silicene sheet is a promising material for spintronics due to its unique magnetic properties. In this study, a first-principle method based on density functional theory (DFT) is used to investigate the stability, electronic, and magnetic properties of edge hydrogenated and fluorinated SiNRs. Edge functionalization of all possible types of SiNRs such as armchair, zigzag, Klein, reconstructed Klein, pentagon-heptagon, and the combination of the edges are studied. It is found that edge fluorinated structures are much more stable than that of edge hydrogenated. It is also discovered that tri-fluorinated Klein edge SiNR and di-hydrogenated armchair edge SiNR are the most stable structures when the edges are terminated with fluorine and hydrogen atoms, respectively. While, the symmetric edge functionalized zigzag SiNRs show antiferromagnetic semiconductor behaviour. Considering spin-polarization, the asymmetry in edge functionalization bring various and extraordinary magnetic states, such as SGS, ferromagnetic metals or semiconductors, and antiferromagnetic metals. In order to discover the effects of doping on the magnetic and electronic properties of edge functionalized SiNRs, N- or B-doped SiNRs are considered. It is revealed that the dopants energetically prefer to be substituted with Si atoms at the edge of SiNRs. Interestingly, the remarkable SGS and half-metal character, as well as ferromagnetic metallic behavior are observed in N- or B- doped armchair, zigzag, and Klein edge SiNRs which are highly advantageous for spintronics applications. These new findings encourage further experimental investigations in the development of SiNRs based nanoelectronics with spin tuning.

Electrical and magnetic properties of nanocrystalline Fe 100−xNi x alloys

The electrical and magnetic properties of nanocrystalline binary Fe 100− x Ni x alloys, where x ranges from 0 to 100, prepared by a combination of aqueous and solid-state reduction processes have been studied vis-à-vis their microstructure. The microstructural studies indicate the formation of near-equilibrium phases in the alloys with crystallite size in the range 20–40 nm. The crystallite size in the case of pure Fe and Ni, however, is in the range 40–80 nm. The electrical transport in the temperature range 20–300 K exhibits a typical ferromagnetic metallic behavior in all the cases and the absolute resistivity of nanocrystalline Fe 100− x Ni x alloys decreases monotonically with increasing Ni content. The saturation magnetization of the alloys on the other hand decreases progressively with Ni addition towards that of pure Ni value. The coercivity of alloys is found to be independent of temperature in the range 5–300 K except in the case of pure Ni wherein it increases from 30 Oe at 300 K to 65 Oe at 5 K. The electrical and magnetic properties of the nanocrystaline Fe–Ni alloys do not follow the predictions of simple itinerant band model for alloys. The temperature dependence of saturation magnetization in all the cases has a T 3/2 Bloch variation while the average atomic moment of the alloys has an effective medium composition dependence.

Magnetism and transport of CuCr 2Se 4 thin films

We report on the successful synthesis, magnetism and transport of highly spin-polarized chalcogenide thin films of CuCr 2Se 4, which are promising candidates for spin-based electronic applications. We also present electronic structure calculations for CuCr 2Se 4 that, together with magnetic and transport data, imply that the stoichiometric compound is a metallic ferromagnet with a relatively low density of hole-like carriers at the Fermi energy. These calculations also predict that a deficiency of Se will deplete the minority density of states at the Fermi energy perhaps leading to a half-metal. We have successfully grown thin films of CuCr 2Se 4 by pulsed laser deposition on isostructural MgAl 2O 4 substrates followed by an anneal in a Se-rich environment. X-ray diffraction confirms the structure of CuCr 2Se 4 on MgAl 2O 4 substrates as well as a secondary phase of Cr 2Se 3. X-ray absorption spectroscopy indicates that the chemical structure at the surface of the films is similar to that of bulk CuCr 2Se 4 single crystals. Magnetization measurements indicate that these films saturate with a magnetic moment close to 5 μ B/f.u. and a Curie temperature ( T c) above 400 K. X-ray magnetic circular dichroism measurements show that magnetic order persists to the surface of the film. Resistivity and Hall effect measurements are consistent with p-type ferromagnetic metallic behavior and with the electronic structure calculations.

High Curie temperature in B-site ordered Sr 2CrWO 6 epitaxial thin films

Epitaxial and c-axis oriented double perovskite Sr 2CrWO 6 thin films were prepared on SrTiO 3 (100) and LaAlO 3 (100) substrates by pulsed-laser deposition. Structural, magnetic and transport properties were found to be sensitive to the gas conditions employed during the deposition. A small amount of oxygen along with Ar during the deposition was found to be essential for B-site ordering; such films displayed lattice parameters close to the bulk value and display ferromagnetic metallic behavior. The Curie temperature observed above 500 K in these films is higher than bulk Sr 2CrWO 6 samples. Films grown without oxygen were observed to have long c-parameter and no B-site ordering; they were non-magnetic and semiconducting.

Effect of Pressure on Magnetic and Transport Properties of Pyrochlore Molybdates

The effect of pressure on magnetic and transport properties of pyrochlore molybdates has been studied using single-crystal specimens of (Sm 1- x Tb x ) 2 Mo 2 O 7 , which show ferromagnetic metallic behavior for x < x c (=0.7–0.8) at ambient pressure. It is found that a spin-glass-like metallic state is stabilized under hydrostatic pressure ( p ) through measurements for the specimens near x c for p <1.5 GPa. The application of pressure reveals that there is no correlation between ferromagnetism and metallic behavior in pyrochlore molybdates, in contrast to a double-exchange system.

Electronic phase transition and ferromagnetic ordering in LaMn 0.95− xRu xO 3 ( x≤0.4)

Ruthenium doped B-site deficient compound, LaMn 0.95− x Ru x O 3, where 0≤ x≤0.4 shows a ferromagnetic metal ( x<0.1) to insulator (for x>0.1) transition involving rhombohedral to orthorhombic symmetry change. The ferromagnetic metallic behavior is sustained by a double exchange mediated process, while for x>0.1 a superexchange ferromagnetic interaction is observed. The conduction mechanism in the paramagnetic state for all the compounds is dominated by the 3D-variable range hopping type. The charge carrier localization length, ξ decreases from 2.88 Å at x=0.0 to 1.64 Å for x=0.4. The unusual ferromagnetic interaction between Mn and Ru is explained based on the mixed valence effect.

Electric and magnetic properties of Cu-doped La–Sr manganites

Samples of La 0.89Sr 0.11Mn 1− y Cu y O 3+ δ ( y=0.00, 0.07) were prepared and characterized by magnetic and transport measurements and zero-field nuclear magnetic resonance. All samples displayed ferromagnetic metallic behavior below the ordering temperature, which decreased for the Cu-doped sample. 139La NMR spectra have been observed around 19 MHz for both samples, with remarkable broadening and splitting introduced by the Cu doping. An estimate of the magnetoresistivity and magnetocaloric properties was provided as well.

Oxygen Deficiency Effects upon Structural, Magnetic and Electrical Properties of Doped Manganite Oxides

The effects of the oxygen deficiency on structural, magnetic and electrical properties of La 0.7 Sr 0.3 MnO 3-δ □ δ manganites, where □ is a vacancy (0 ≤ δ < 0.15), have been investigated. The vacancy powder samples were synthesized using a new technique. A structural phase transition separating a rhombohedral phase and an orthorhombic phase was observed at a concentration of Mn 3+ around 85% to 90% per Mn atom in the unit formula. These compounds exhibit ferromagnetic metallic behavior for δ < 0.1 and antiferromagnetic insulator behavior for 0.125 < δ < 0.15. A charge ordering seems to appear below T = 115 K in the La 0.7 Sr 0.3 MnO 2.9 (δ = 0.1) specimen. The structural and magnetic transitions are very sensitive to the vacancy rate.

Charge-Ordering in Manganates

Ordering of Mn3+ and Mn4+ ions occurs in the rare earth manganates of the general composition Ln1-xAxMnO3 (Ln = rare earth, A = Ca, Sr). Such charge-ordering is associated with antiferromagnetic and insulating properties. This phenomenon is to be contrasted with the ferromagnetic metallic behavior that occurs when double-exchange between the Mn3+ and Mn4+ ions predominates. Two distinct types of charge-ordering can be delineated. In one, a ferromagnetic metallic (FMM) state transforms to the charge-ordered (CO) state on cooling. In the other scenario, the CO state is found in the paramagnetic ground state and there is no ferromagnetism down to the lowest temperatures. Magnetic fields transform the CO state to the FMM state, when the average radius of the A-site cations is sufficiently large (〈rA〉 > 1.17 Å). Chemical melting of the CO state by Cr3+ substitution in the Mn site is also found only when 〈rA〉 ≳ 1.17 Å. The effect of the size of the A-cations on the Mn−O−Mn angle is not enough to explain the observed variations of the charge-ordering temperature as well as the ferromagnetic Curie temperature Tc. An explanation based on a competition between the Mn and A-cation orbitals for σ-bonding with the oxygen ρσ orbitals is considered to account for the large changes in Tc and hence the true bandwidth, with 〈rA〉. Effects of radiation, electric field, and other factors on the CO state are discussed along with charge-ordering in other manganate systems. Complex phase transitions, accompanied by changes in electronic and magnetic properties, occur in manganates with critical values of 〈rA〉 or bandwidth. Charge-ordering is found in layered manganates, BixCa1-xMnO3 and CaMnO3-δ.

Epitaxial Growth Mechanism and Physical Properties of Ultra thin Films of La0.6Sr0.4MnO3

ABSTRACTThin films of La1-xSrxMnO3 (x=0.4) were fabricated using pulsed laser deposition (PLD) methods. The surface morphology of the films was sensitively affected by oxygen pressure during deposition. At high oxygen pressure (∑150 mTorr), randomly aligned grains were nucleated on the epitaxial film. When the pressure was reduced to 100 mTorr, the epitaxial film had very smooth surface. Under this condition, the thickness dependence of resistivity and magnetization were analyzed. Even 6 nm thick film showed ferromagnetic metallic behavior. The AFM images of ulta thin films deposited on wet-etched SrTiO3 showed atomically flat terraces and 0.4 nm steps. The film growth mode can be tuned to either layer by layer or step flow by the deposition temperature.