Minority Gap Research Articles

Enhancement of electric polarization in ultrathin half-metallic [BaFeO3]m/[BaTiO3]n superlattices : an ab initio study

This theoretical study investigated ultrathin [BaFeO3]m/[BaTiO3]n superlattices with varying periodicities m/n from 1 to 4. At structural level, important relaxations occur, resulting in Ti-O, Fe-O, and Ba-O ferroelectric displacements. The Ti-O displacements in our superlattices reached an amplitude of 32.8 % which is larger than its bulk value in BaTiO3 of 0.125 Å. In addition, Fe-O displacements in the range of [0.043, 0.122] Å appeared in the BaFeO3 layers of m/n superlattices. The electronic structure analysis revealed a half-metallic character in all m/n systems. A clear dependence between the minority gap and m/n periodicities was observed in the DOS plots. Two categories of superlattices were distinguished from the electric polarization calculations. The first includes 1/1, 2/3, 3/2, and 4/1 with a polarization comparable to the bulk value of BaTiO3. The second category includes the 2/1, 1/2, 1/3, 3/1, and 1/4 systems with polarization amplitudes of 30% larger than the BaTiO3 bulk value. All m/n superlattices remained ferromagnetic. These findings paved the way to new promising applications of those ultrathin superlattices with tunable electronic properties.

Gender and Race Demographics of Fellowships After General Surgery Training in the United States: A Five-Year Analysis in Applicant and Resident Trends.

The gender and minority gap in general surgery residency is narrowing; however, literature lacks comprehensive data regarding the demographics of fellowship programs following general surgery training. Data from 2017 to 2021 for gender, ethnicity, and surgical subspecialty are publicly available from the ERAS database and ACGME yearly data reports. Cochran-Armitage trend tests were used to determine statistical significance in trends for female and minority applicants and trainees. The overall trend of female applicants to surgical specialties remained stagnant. However, female applicants to vascular surgery increased significantly from 25% to 35% (P = .045). There was no significant increase in female trainees in any surgical specialties evaluated. Furthermore, the overall trend of minority applicants to surgical specialties also remained stagnant, except for pediatric surgery, which showed significantly fewer minority applicants. Despite pediatric surgery having fewer applicants, minority trainees in this specialty increased significantly from 8% to 19% (P = .008). Several current initiatives, such as intentional mentorship, are being reported to promote diverse and equal representation among female and minority applicants and trainees. However, the current overall margin of increase in diversity among surgical specialty applicants and trainees is minimal, indicating that continued efforts are needed to diversify surgical specialty training programs.

Enhanced Magnetic Properties of Electrodeposited Co2FeSn Film with High Structural Order

Near stoichiometric Co2FeSn Heusler alloy films with a highly ordered L2 1 structure and mean grain size of 23 ± 1 nm have been prepared on a polycrystalline copper substrate for the first time by electrodeposition route. Deposition potential −4.0 V yielded the stoichiometric alloy composition in the potentiostatic mode. The highly disordered as-deposited alloy film crystallized into the ordered stable Heusler alloy structure upon heat treatment under vacuum. The heat-treated film exhibited the highest magnetic moment (5.18 ± 0.04 μ B/f.u. at 5 K) and Curie temperature (1123 K) ever achieved in this alloy in any form. The very high value of K eff (∼106 erg c.c.−1) obtained for this alloy makes this alloy promising for high-density magnetic recording application. Ab initio studies using GGA + U approach provide information on the minority gap near the Fermi level and its tunability as a function of the electron correlation factor represented by the Hubbard parameter U.

Racial Diversity, Majority–Minority Gap, and Confidence in the Criminal Justice System

Racial status, that is, majority/minority identity, affects an individual’s confidence in the criminal justice system, and this effect could vary across social contexts. We analyzed people’s confidence in the criminal justice system comparatively in 88 societies using the World Values Survey (1981–2020). Results from the hierarchical linear models showed the following patterns: (1) Racial majority members display higher confidence in the criminal justice system than minority members; (2) the majority advantage in confidence is greater when racial diversity increases; (3) the majority advantage is most salient in societies with Black or Arabic majorities. The results suggest that majority members’ higher trust in order institutions is associated with perceived advantages and social comparison with minority members. Our findings reveal the profound interactive effects of racial status and context on confidence in the criminal justice system, shed light on racial diversity, and contribute new knowledge to public opinion studies.

The Role of Credit Attributes in Explaining the Homeownership Gap Between Whites and Minorities Since the Financial Crisis, 2012–2018

ABSTRACT Homeownership rates have been slow to recover since the financial crisis. Minority groups such as Blacks and Hispanics have been particularly slow to transition to homeownership. Using uniquely constructed anonymized household panel data obtained from a credit bureau, we find that Blacks and Hispanics were, respectively, one half and two thirds as likely as Whites to transition to mortgage ownership between 2012 and 2018. We analyze the role of credit attributes, among other factors, in explaining the racial/ethnic gap in transition to mortgage ownership by 2018 for a sample of individuals who were nonmortgage holders in 2012. Using the Blinder–Oaxaca decomposition technique for nonlinear equations, we find that racial/ethnic differences in credit attributes explain a large portion of the White–minority gap in the transition rates. However, there are key differences in experience across the two minority groups. Whereas racial/ethnic differences in geographic location contribute substantially to the White–Hispanic gap in the mortgage transition rate, racial/ethnic differences in household composition and income growth matter more in explaining the White–Black gap in the mortgage transition rate. Lastly, we find there is considerable heterogeneity across states in the contribution of credit attributes and geography to the White–minority gap in the transition rate.

The racial/ethnic gap in financial literacy in the population and by income

AbstractWe investigate the determinants of the racial/ethnic gap in financial literacy in the general population and within income classes, with a focus on childhood family circumstances and neighborhood socioeconomic characteristics. Our model explains 48% and 57% of the observed gap for Blacks and Hispanics, respectively. For both groups, differences in individual characteristics and neighborhood socioeconomic status contribute the most to the explained gap. The White–Minority gap narrows when moving from low‐ to high‐income classes, but the ability of the model to explain it decreases monotonically. Identifying which additional barriers put minorities at a disadvantage is key to improve financial literacy.

Vietnam: country report on children's environmental health.

As a developing country, Vietnam is facing many problems such as environmental pollution caused by industrialization, urbanization and the ethnic minority gap. Besides, Vietnam is one of the 10 countries most vulnerable to the effects of climate change and natural disasters. Vietnam has more than 26.3 million children under 16 years of age, with the ratio being 114 boys/100 girls. Children are especially vulnerable to environmental risks. This review includes much data collected during 2010-2018 on children's environmental health in Vietnam.

Creation and Confidence: BME students as academic partners….but where were the staff?

This Case Study documents the REACT project 'Creation and Confidence' based at Sheffield Hallam University, which has a larger-than-expected Black Minority and Ethnic (BME) attainment gap; hence, this student group has been constructed as 'hard to reach'. The project team consisted of a range of academic and professional services staff alongside three dedicated student researchers. The project set out to achieve: gaining evidence-based insights into the use of co-design and peer-learning as conduits of confidence-building for and belonging of BME students; developing a scalable approach to building confidence for and fostering belonging of all students; raising awareness of the need to think differently about explanations for BME underachievement. In reality, the team found that staff engagement constituted the biggest barrier, as - no matter how much incontrovertible evidence was presented - other facets of institutional provision were always identified as having priority, which resulted in inertia. This study documents the emotional labour of trying to effect change within a resistant culture. Whilst some of the aims remain unachieved – and, arguably, were always going to be unachievable - there have been some very positive developments and enlightening lessons.

Effect of low-valent atom substitution on electronic structure and magnetic properties of Fe 1.5M 0.5CoSi (M=V, Cr, Mn, Fe) Heusler alloys

Quaternary Heusler alloys Fe 1.5M 0.5CoSi with M=V, Cr, Mn and Fe have been investigated theoretically and experimentally. All of these samples crystallize in the ordered Heusler-type structure. The calculated electronic structure shows a pseudogap around E F in the minority spin states of Fe 2CoSi. With the substitution of low-valent atoms for Fe, the majority antibonding peak is shifted to higher energy and a minority gap around the Fermi level is opened. High spin polarization ratio is obtained in Fe 1.5M 0.5CoSi (M=V, Cr, Mn) alloys. The calculated total spin moments decrease with decreasing number of valence electrons and follow the Slater–Pauling curve, which agree with the experimental results well. The Curie temperature decreases as M atom varies from Fe to V, but is always higher than 650 K, which is suitable for technical applications.

Hall effect and electronic structure of [formula omitted] films

Tunneling experiments have shown that in order to retain half-metallicity at room temperature not only a large gap is required but also a Fermi energy considerably distant from the minority band edges. We correlate the position of the Fermi energy in the spin minority gap obtained from band structure calculations to Hall effect experiments. As a model system we chose Co 2 Fe x Mn 1 - x Si , where the Fermi energy was calculated to move from the valence band edge of the minority states to the conduction band edge with increasing x. On high quality laser ablated epitaxial films we observe a sign change of both the normal and the anomalous Hall effect with doping. The experimental data agree with band structure calculations done in the LSDA + DMFT scheme.

Effects of post-growth annealing on structural and compositional properties of the Co2Cr0.6Fe0.4Al surface and its relevance for the surface electron spin polarization

In this study we investigate the influence of post-growth annealing on different Co2Cr0.6Fe0.4Al samples. We find strong changes in the geometric surface structure as well as in the element specific concentrations during the annealing process. These irreversible changes go in hand with characteristic changes in the electron spin polarization (ESP) at the surface: as observed in Cinchetti et al (2007 J. Phys. D: Appl. Phys. 40 1544), the iron buffered sample shows the largest spin polarization at the Fermi level. The latter remains positive as a consequence of the reduced density of states for the minority carriers due to the predicted minority gap, which can be clearly seen for all samples above the proposed minimum annealing temperature of 400 °C. Above this temperature we observe a characteristic dip in the ESP as a sign of increasing structure quality. It appears at 0.6 eV binding energy and is consistent with a peak in the minority electron density of states seen in both experiment and theory.

Chapter 9 - Half-Metallic Systems: Complete Asymmetry in Spin Transport

There are systems with metallic spin-up and spin-down electrons, that is, both spins contribute to the Fermi level density of state (and transport). For highly spin polarized systems, it can be envisioned having a situation where one spin channel shows metallicity while the other spins are insulating. Such materials, where tunneling currents show 100% spin polarization when used in tunneling devices, have been found and are called half-metals. Half-metals have unusual electronic properties. For one type of spin, the half-metal looks metallic with a well defined Fermi surface. For the opposite spin, there is a gap in the state density. In half-metals, there is a clear gap in the density of states corresponding to one type of spin. These half-metals do conduct electricity but do not show a high field magnetic susceptibility. All half-metals contain more than one element with most of them being oxides or Heusler type alloys. In real half-metals, conduction is carried out almost entirely by one spin channel. There is no clear experimental signal to identify half-metals. If the minority (or majority) gap is a true gap (with zero total density of states) then it is possible to conclude that the majority and minority counts of spin have to be integers per unit cell. The band gap for one spin type is the defining feature of these materials, therefore, the chapter are the three different categories of gaps—covalent band gaps, charge-transfer gaps, and d-d band gaps. Half-metals in different categories listed above respond differently to external parameters such as pressure because of different electronic structures that give rise to half-metallicity in these three categories. The chapter discusses half Heusler alloys: NiMnSb and PtMnSb, full Heusler alloys: Co 2 MnSi, Co 2 MnGe, Co 2 Cr 1-x Fe x Al, chromium dioxide, perovskites and double-perovskites, and multilayers of zincblende half-metals with semiconductors.

Calculated electronic and magnetic properties of the half-metallic, transition metal based Heusler compounds

In this paper, results of ab initio band structure calculations for A2BC Heusler compounds that have A and B sites occupied by transition metals and C by a main group element are presented. This class of materials includes some interesting half-metallic and ferromagnetic properties. The calculations have been performed in order to understand the properties of the minority band gap, the peculiar transport properties and magnetic behaviour found in these materials. Among the interesting aspects of the electronic structure of the materials are the contributions from both A and B atoms to the total magnetic moment. The magnitude of the total magnetic moment shows a trend consistent with the Slater–Pauling type behaviour in several classes of these compounds. The total magnetic moment also depends on the kind of C atoms although they do not directly contribute to it. In Co2 compounds, a change of the C element changes the contribution of the t2g states to the moment at the Co sites. The localized moment in these magnetic compounds resides at the B site. Other than in the classical Cu2-based Heusler compounds, the A atoms in Co2, Fe2 and Mn2-based compounds may contribute significantly to the total magnetic moment. It is shown that the inclusion of electron–electron correlation in the form of LDA + U calculations helps to understand the magnetic properties of those compounds that already exhibit a minority gap in calculations where it is neglected. Besides the large group of Co2 compounds, half-metallic ferromagnetism was here found only in such compounds that contain Mn.

Ab initio electronic and magnetic structure inLa0.66Sr0.33MnO3: strain and correlation effects

The effects of tetragonal strain on the electronic and magnetic properties of strontium-doped lanthanummanganite, La2/3Sr1/3MnO3 (LSMO), are investigated by means of density-functional methods. As far as the structuralproperties are concerned, the comparison between theory and experiments forLSMO strained on the most commonly used substrates shows an overall goodagreement: the slight overestimate (at most of 1–1.5%) for the equilibriumout-of-plane lattice constants points to possible defects in real samples. The inclusionof a Hubbard-like contribution on the Mn d states, according to the so-called‘LSDA+U’ approach, is rather ineffective from the structural point of view, but much more importantfrom the electronic and magnetic point of view. In particular, full half-metallicity,which is missed within a bare density-functional approach, is recovered withinLSDA+U, in agreement with experiments. Moreover, the half-metallic behaviour, particularlyrelevant for spin-injection purposes, is independent of the chosen substrate and is achievedfor all the considered in-plane lattice constants. More generally, strain effectsare not seen to crucially affect the electronic structure: within the consideredtetragonalization range, the minority gap is only slightly (i.e. by about 0.1–0.2 eV) affectedby a tensile or compressive strain. Nevertheless, we show that the growth on asmaller in-plane lattice constant can stabilize the out-of-plane versus in-planeeg orbital and significantly change their relative occupancy. Sinceeg orbitals are key quantities for the double-exchange mechanism, strain effects are confirmedto be crucial for the resulting magnetic coupling.

Stability and half-metallicity of transition metal pnictides in tetrahedrally bonded structures

Using a full potential linearized muffin-tin approach and the spin polarized density functional method, we studied the magnetism and the electronic structure for transition metal pnictides in the zinc blende sZBd and the wurtzite sWZd structures under volume expansion and compression. It was found that for many compounds the WZ structure has lower total energy than the ZB structure. The energy difference between the two tetrahedrally bonded structures are only a few meV, which indicates that the system may form other polytypes with stacking intermediate between ZB and WZ. Both ZB and WZ structure are half-metallic. There are only slight differences between ZB and WZ structures in the resulting band gaps of the minority spin and the density of states sDOSd at the Fermi level for the majority spin. This indicates that these properties are only determined by the local bonding. The minority gap and the DOS at the Fermi level are found to be strongly dependent on the volume expansion.

Understanding the electronic structure, optical, and vibrational properties of theFe8Br8single-molecule magnet

We present the results of our all-electron density functional calculation on the electronic structure and optical properties of ${[{\mathrm{Fe}}_{8}{\mathrm{O}}_{2}{(\mathrm{O}\mathrm{H})}_{12}{({\mathrm{C}}_{6}{\mathrm{H}}_{15}{\mathrm{N}}_{3})}_{6}{\mathrm{Br}}_{6}]}^{2+}$, the functional building block of the $[{({\mathrm{C}}_{6}{\mathrm{H}}_{15}{\mathrm{N}}_{3})}_{6}{\mathrm{Fe}}_{8}{({\ensuremath{\mu}}_{3}\ensuremath{-}\mathrm{O})}_{2}{({\ensuremath{\mu}}_{2}\ensuremath{-}\mathrm{O}\mathrm{H})}_{12}]{\mathrm{Br}}_{7}({\mathrm{H}}_{2}\mathrm{O})\mathrm{Br}.8{\mathrm{H}}_{2}\mathrm{O}$ single-molecule magnet. The calculated results are compared with the experimentally measured optical spectrum, and the primary features of the excitations are assigned. Excellent agreement is obtained. The calculated spin minority gap is $0.23\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, the spin majority gap is $0.54\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, and the spin majority to minority gap is $0.15\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Notably, the low-energy spin minority gap is not a dipole-allowed excitation. Experimentally, we find that $[{({\mathrm{C}}_{6}{\mathrm{H}}_{15}{\mathrm{N}}_{3})}_{6}{\mathrm{Fe}}_{8}{({\ensuremath{\mu}}_{3}\ensuremath{-}\mathrm{O})}_{2}{({\ensuremath{\mu}}_{2}\ensuremath{-}\mathrm{O}\mathrm{H})}_{12}]{\mathrm{Br}}_{7}({\mathrm{H}}_{2}\mathrm{O})\mathrm{Br}.8{\mathrm{H}}_{2}\mathrm{O}$ is a semiconductor, with a dipole-allowed optical gap of approximately $0.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ (peak position at $\ensuremath{\sim}0.9\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$) and an additional optically observable electronic excitation centered at $0.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The latter feature is weak and broad, with superimposed ($\mathrm{C}\mathrm{H}$, $\mathrm{N}\mathrm{H}$, and $\mathrm{O}\mathrm{H}$) vibrational structure. We suggest that the $0.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ peak in the optical conductivity may be attributable to the spin majority highest occupied molecular orbital to spin minority lowest unoccupied molecular orbital excitation, activated by inclusion of spin-orbit coupling, which mixes states of different symmetry and spin. Overall, we find that the low-energy excitations are dominated by $\mathrm{Fe}\phantom{\rule{0.3em}{0ex}}d\ensuremath{\rightarrow}\mathrm{Fe}\phantom{\rule{0.3em}{0ex}}d$ interionic excitations and that the dipole-allowed excitations involve antiferromagnetically coupled pairs of Fe ions. At higher energy, the features are primarily due to $\mathrm{O}\phantom{\rule{0.3em}{0ex}}p\ensuremath{\rightarrow}\mathrm{Fe}\phantom{\rule{0.3em}{0ex}}d$ charge transfer transitions. A discussion of the vibrational properties is also included along with an analysis of how the electronic structure results support reduced moments on the minority spin Fe ions.

Electronic and magnetic properties of the (1 1 1) surfaces of NiMnSb

Using an ab initio electronic structure method, I study the (1 1 1) surfaces of the half-metallic NiMnSb alloy. In all cases there is a very pronounced surface state within the minority gap which destroys the half-metallicity. This state survives for several atomic layers below the surface contrary to the (0 0 1) surfaces where surface states were located only at the surface layer. The lower dimensionality of the surface leads in general to large enhancements of the surface spin moments.

Analyzing the Minority Gap in Achievement Scores: Issues for States and Federal Government

The No Child Left Behind Act of 2001 requires that states demonstrate a reduction in the test score minority gap over time but does not specify what methodology states must use to demonstrate this. The Act also requires that a measure of Adequate Yearly Progress be established by each state expressed in terms of the percent of students who achieve a level of “proficiency” on the state examination. While the most common methods used by states for analyzing the minority gap in test scores over time are percent achieving a performance standard, mean scale scores, and effect sizes, the default method for analyzing the minority gap will likely be the percent achieving proficiency. This article considers some of the practical issues involved in using the percent achieving a performance standard, mean scale scores, and effect sizes to analyze the minority gap using Texas student performance on their in‐state assessment, National Assessment of Educational Progress (NAEP), and SAT. The intent of the article is to increase the understanding of policymakers and others on the issues of using the various statistics to analyze the minority gap.