Compositional tuning of ferromagnetism in Ga1-xMnxP

ManuscriptWe report the magnetic and transport properties of Ga1-xMnxP synthesized via ion implantation followed by pulsed laser melting over a range of x, namely 0.018 to 0.042. Like Ga1-xMnxAs, Ga1-xMnxP displays a monotonic increase of the ferromagnetic Curie temperature with x associated with the hole-mediated ferromagnetic phase while thermal annealing above 300 ºC leads to a quenching of ferromagnetism that is accompanied by a reduction of the substitutional fraction of Mn. However, contrary to observations in Ga1- xMnxAs, Ga1-xMnxP is non-metallic over the entire composition range. At the lower temperatures over which the films are ferromagnetic, hole transport occurs via hopping conduction in a Mn-derived band; at higher temperatures it arises from holes in the valence band which are thermally excited across an energy gap that shrinks with x

Electrical transport and ferromagnetism in Ga1−xMnxAs synthesized by ion implantation and pulsed-laser melting

Journal ArticleWe present a detailed investigation of the magnetic and magnetotransport properties of thin films of ferromagnetic Ga1−xMnxAs synthesized using ion implantation and pulsed-laser melting (II-PLM). The field and temperature-dependent magnetization, magnetic anisotropy, temperature-dependent resistivity, magnetoresistance, and Hall effect of II-PLM Ga1−xMnxAs films have all of the characteristic signatures of the strong p-d interaction of holes and Mn ions observed in the dilute hole-mediated ferromagnetic phase. The ferromagnetic and electrical transport properties of II-PLM films correspond to the peak substitutional Mn concentration meaning that the nonuniform Mn depth distribution is unimportant in determining the film properties. Good quantitative agreement is found with films grown by low temperature molecular beam epitaxy and having the similar substitutional MnGa composition. Additionally, we demonstrate that II-PLM Ga1−xMnxAs films are free from interstitial MnI because of the high-temperature processing. At high Mn implantation doses, the kinetics of solute redistribution during solidification alone determine the maximum resulting MnGa concentration. Uniaxial anisotropy between in-plane [1¯10] and [110] directions is present in II-PLM Ga1−xMnxAs giving evidence for this being an intrinsic property of the carrier-mediated ferromagnetic phase

Hydrogen patterning of Ga1-xMnxAs for planar spintronics

We demonstrate two patterning techniques based on hydrogen passivation of Ga1-xMnxAs to produce isolated ferromagnetically active regions embedded uniformly in a paramagnetic, insulating host. The first method consists of selective hydrogenation of Ga1-xMnxAs by lithographic masking. Magnetotransport measurements of Hall-bars made in this manner display the characteristic properties of the hole-mediated ferromagnetic phase, which result from good pattern isolation. Arrays of Ga1-xMnxAs dots as small as 250 nm across have been realized by this process. The second process consists of blanket hydrogenation of Ga1-xMnxAs followed by local reactivation using confined low-power pulsed-laser annealing. Conductance imaging reveals local electrical reactivation of micrometer-sized regions that accompanies the restoration of ferromagnetism. The spatial resolution achievable with this method can potentially reach <100 nm by employing near-field laser processing. The high spatial resolution attainable by hydrogenation patterning enables the development of systems with novel functionalities such as lateral spin-injection as well as the exploration of magnetization dynamics in individual and coupled structures made from this novel class of semiconductors.Comment: ICDS-24, July 2007. 8 pages with 4 figure

Electrical transport and ferromagnetism in Ga1-xMnxAs synthesized by ion implantation and pulsed-laser melting

We present a detailed investigation of the magnetic and magnetotransport properties of thin films of ferromagnetic Ga1-xMnxAs synthesized using ion implantation and pulsed-laser melting (II-PLM). The field and temperature-dependent magnetization, magnetic anisotropy, temperature-dependent resistivity, magnetoresistance, and Hall effect of II-PLM Ga1-xMnxAs films have all of the characteristic signatures of the strong p-d interaction of holes and Mn ions observed in the dilute hole-mediated ferromagnetic phase. The ferromagnetic and electrical transport properties of II-PLM films correspond to the peak substitutional Mn concentration meaning that the non-uniform Mn depth distribution is unimportant in determining the film properties. Good quantitative agreement is found with films grown by low temperature molecular beam epitaxy (LT-MBE) and having the similar substitutional Mn_Ga composition. Additionally, we demonstrate that II-PLM Ga1-xMnxAs films are free from interstitial Mn_I because of the high temperature processing. At high Mn implantation doses the kinetics of solute redistribution during solidification alone determine the maximum resulting Mn_Ga concentration. Uniaxial anisotropy between in-plane [-110]and [110] directions is present in II-PLM Ga1-xMnxAs giving evidence for this being an intrinsic property of the carrier-mediated ferromagnetic phase

Beneficial effect of high energy intake at lunch rather than dinner on weight loss in healthy obese women in a weight-loss program: a randomized clinical trial

ABSTRACT Background: The association between the time of nutrient intake and health has been described in a few studies. To our knowledge, no study has evaluated the relation between high energy intakes at lunch compared with at dinner on weight loss in overweight and obese subjects. Objective: We compared the effect of high energy intake at lunch with that at dinner on weight loss and cardiometabolic risk factors in women during a weight-loss program. Design: Overweight and obese women [n = 80; body mass index (BMI; in kg/m2): 27–35; age: 18–45 y] were asked to eat either a main meal at lunch (LM) or a main meal at dinner (DM) for 12 wk while in a weight-loss program. Results: A total of 80 participants were randomly assigned to one of 2 intervention groups. Sixty-nine subjects (86%) completed the trial (34 subjects in the DM group, and 35 subjects in the LM group). Baseline variables were not significantly different between groups. A significant reduction in anthropometric measurements and significant improvements in cardiometabolic risk characteristics were observed over 12 wk in both groups. Compared with the DM group, the LM group had greater mean 6 SD reductions in weight (LM: 25.85 6 1.96 kg; DM: 24.35 6 1.98 kg; P = 0.003), BMI (LM: 2.276 0.76; DM: 1.68 6 0.76; P = 0.003), homeostasis model assessment of insulin resistance (LM: 20.66 6 0.33; DM: 20.46 6 0.24; P = 0.001), and fasting insulin (LM: 22.01 6 1.10 mIU/mL; DM: 21.16 6 0.72 mIU/mL; P , 0.001) after 12 wk. However, there were no significant differences for fasting plasma glucose and lipid profiles within both groups after 12 wk. Conclusions: The consumption of higher energy intake at lunch compared with at dinner may result in favorable changes in weight loss in overweight and obese women after a weight-loss program of 12 wk. The consumption may also offer clinical benefits to improve insulin resistance. This trial was registered at clinicaltrials.gov as NCT02399280. Am J Clin Nutr doi: 10.3945/ajcn.116.134163

Effect of a long bout versus short bouts of walking on weight loss during a weight loss diet: a randomized trial

Objective: To evaluate the effect of different daily physical activity (PA) frequencies while maintaining the same daily volume of PA on weight loss, carbohydrate and lipid metabolism, in women with overweight/obesity throughout a 24- week intervention.Methods: 65 women [BMI = 27- 35 kg/m²; age= 18-40 y] who had a sedentary lifestyle were randomly allocated to include either a longer-bout of PA (LBP), 50 min/d moderate-intensity PA, or two shorter-bouts of PA (SBP), two 25 min/d moderate intensity PA, 6 d/week during their weight loss plan. Anthropometric and blood measurements were taken at baseline and 24 weeks.Results: Compared with the LBP group, the SBP group had a greater decrease in weight (SBP: -8.08 ± 2.20 kg; LBP: -6.39 ± 2.28 kg; P = 0.019), BMI (SBP: -3.11 ± 0.87 kg/m²; LBP: -2.47 ± 0.86 kg/m², P=0.027) and waist circumference (SBP: -8.78 ± 2.62 cm; LBP: -5.76 ± 2.03 cm; P = 0.026). No significant differences were seen in carbohydrate and lipid metabolism characteristics after the 24 weeks.Conclusion: PA undertaken in 2 shorter-bouts per day could be more effective for weight loss than when undertaken in a daily long-bout in adult women on a 24 wk weight loss program

Assessment of resistance and non-resistance fractions of heavy metals concentration (Fe, Mn, Cr, Ni) in surface sediments from the southern of Caspian Sea of two stations (Tonekabon and Amirabad)

This study was conducted to determine some heavy metals (Fe, Mg, Cr, Ni) of surface sediment in the southern Caspian Sea during two seasons (Summer and Winter) in 2014-2015. 36 surface sediments samples (with triplicate) were collected at two stations (Tonekabon and Bandar Amirabad). All samples were analyzed using sequential extraction to indicate natural and anthropogenic sources. The results indicated that the percentage of non-resistance fraction in Tonekabon area were measured 3.5,45.0, 22.1 and 6.0 for Fe, Mg, Cr, Ni, respectively and in Amirabad area were 23.0,2.6,1.8 and 4.0, respectively. On the other hand, the percentage of resistance fraction values were obtained 96.5, 55.0, 77.9 and 94.0 in Tonekabon, and 77.0, 97.4, 98.2, and 96.0 in Amirabad region. The chemical speciation of Fe, Mg, Cr, Ni in most sampling stations were in the order of residual> oxidisableorganic > acid-reducible >exchangeable. The order of total concentration, non-resistance and resistance fraction were observed Fe>Mn>Ni>Cr, Mn>Fe>Ni>Cr and Fe>Mn>Ni>Cr, respectively. As a conclusion, results of total concentration, resistnace and non-resistance of Fe, Mn, Ni and Cr were lower than standard and earth shell (Igeo) in this area. This is shown that surface sediments of this area were not polluted with these heavy metals and bio available fraction provides little indication of potential interactions with the biotic components present in this environment

Defect-mediated metastability and carrier lifetimes in polycrystalline (Ag,Cu)(In,Ga)Se-2 absorber materials

Using a combination of optical and electrical measurements, we develop a model for metastable defects in Ag-alloyed Cu(In,Ga)Se-2, one of the leading thin film photovoltaic materials. By controlling the pre-selenization conditions of the back contact prior to the growth of polycrystalline (Ag,Cu)(In,Ga)Se-2 absorbers and subsequently exposing them to various stresses (light soaking and dark-heat), we explore the nature and role of metastable defects on the electro-optical and photovoltaic performance of high-efficiency solar cell materials and devices. Positron annihilation spectroscopy indicates that dark-heat exposure results in an increase in the concentration of the selenium-copper divacancy complex (V-Se-V-Cu), attributed to depassivation of donor defects. Deep-level optical spectroscopy finds a corresponding increase of a defect at E-v+0.98eV, and deep-level transient spectroscopy suggests that this increase is accompanied by a decrease in the concentration of mid-bandgap recombination centers. Time-resolved photoluminescence excitation spectroscopy data are consistent with the presence of the V-Se-V-Cu divacancy complex, which may act as a shallow trap for the minority carriers. Light-soaking experiments are consistent with the V-Se-V-Cu optical cycle proposed by Lany and Zunger, resulting in the conversion of shallow traps into recombination states that limit the effective minority carrier recombination time (and the associated carrier diffusion length) and an increase in the doping density that limits carrier extraction in photovoltaic devices.Peer reviewe