Lowell E. Wenger

Fabrication and characterization of Co1−xFex alloy nanowires

Co1−xFex alloy nanowires with 40 nm diam and x=0–1.0 were fabricated by electrodeposition in nanopores of alumina templates. The crystalline structure of the nanowires is concentration dependent and shows a transition from the cobalt hexagonal-closed-packed structure (hcp) to a face-centered-cubic structure (fcc) in the concentration range 0<x<0.1. For an iron content greater than 15 at % the structure becomes body-centered-cubic (bcc). The nanowires with an aspect ratio of about 8 show a highly anisotropic magnetization with the easy axis along the length of the wire. The squareness of the hysteresis loops is between 72% and 93% for magnetic fields parallel to the wires while the squareness is less than 13% for fields perpendicular to the wires. The coercivity along the easy axis reaches a maximum of 2150 Oe for x=0.55 and is almost concentration independent for 0.5<x<0.6.

X-ray photoelectron spectroscopy (XPS) and magnetic susceptibility studies of vanadium phosphate glasses

Vanadium phosphate glasses with the nominal chemical composition [(V2O5)x(P2O5)1 x], where x = 0.30, 0.40, 0.50, and 0.60, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. Asymmetries found in the O 1s, P 2p, and V 2p core level spectra indicate the presence of primarily P–O–P, P–O–V, and V–O–V structural bonds, a spin–orbit splitting of the P 2p core level, and more than one valence state of V ions being present. The magnetic susceptibility data for these glasses follow a Curie–Weiss behavior which also indicates the presence of some V ions existing in a magnetic state, i.e., a valence state other than that of the non-magnetic V. From qualitative comparisons of the abundance of the bridging oxygen or P–O–P sites as determined from the areas under the various O 1s peaks with the abundances of differing phosphate structural groups associated with the presence of different valence states of the vanadium ions, a glass structure model consisting of a mixture of vanadate phosphate phases is proposed for these glass samples. These include V2O5, VOPO4, (VO)2P2O7, VO(PO3), and V(PO3)3 with the abundance of orthophosphate (PO4) 3 units increasing with increasing vanadium content. 2009 Elsevier B.V. All rights reserved.

X-ray Photoelectron Spectroscopy (XPS) and Magnetization Studies of Iron–Vanadium Phosphate Glasses

Abstract Iron–sodium borate glasses with the chemical composition [(B2O3)0.70−x(Na2O)0.3(Fe2O3)x], where 0.00⩽x⩽0.15, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. The core-level binding energies of O 1s, B 1s, and Fe 2p have been measured with both O 1s and B 1s peaks shifting by about 2 eV towards smaller binding energies in the Fe-containing borate glasses while the Fe 2p3/2 and 2p1/2 core levels for the glasses remain essentially unchanged from those of Fe2O3 powder. The O 1s spectrum is deconvoluted into two peaks and the variation in the ratio of the peak areas is discussed in terms of the local iron structure. We suggest that both X-ray photoelectron spectroscopy and magnetization measurements show that the Fe ions remain essentially in one oxidation state, probably Fe3+, for the Fe borate glasses. In addition, the appearance of a large hysteresis between the zero field-cooled and field-cooled magnetization data indicate that the Fe moments are clustered and that the predominant interaction is antiferromagnetic.

Temperature dependence of the magnetization reversal in Co(fcc)–BN–Co(poly hcp) structures

The magnetic properties of multilayer structures with two magnetic layers of the same metal (Co) but with different crystallographic structures separated by an insulating BN layer have been studied. These structures were prepared on Si (001) substrates by a combination of molecular beam epitaxy (metallic layers) and electron cyclotron resonance-assisted sputtering (BN layer). An fcc Co single-crystal layer (60 A) was first stabilized by growing it on a copper fcc buffer layer and subsequently a polycrystalline Co layer (70 A) with hcp structure was grown on top of the insulating BN layer. A CoO antiferromagnetic layer, formed adjacent to this hcp Co layer, significantly influenced the magnetic behavior of the polycrystalline hcp Co layer. The magnetic hysteresis loops for these structures were measured at temperatures ranging from 5 to 350 K with the magnetic field applied along the easy (110) in-plane axis of the fcc Co. A very sharp flipping of the magnetization was found for the fcc Co layer with a nea...

Rapid thermal annealing of YBaCuO films on Si and SiO2 substrates

A very rapid thermal annealing technique has been employed on sputter‐deposited YBaCuO films. After an O2 anneal (with or without a N2 preanneal) at temperatures as high as 920 °C for 8–12 s, films on (100)Si and on SiO2 /Si substrates exhibited superconductivity onsets above 95 K and zero resistance in the range 40–66 K.

Eating tasty food to cope. Longitudinal association with BMI.

The goals of this study were to determine if a change in certain motives to eat highly palatable food, as measured by the Palatable Eating Motives Scale (PEMS), could predict a change in body mass index (BMI) over time, to assess the temporal stability of these motive scores, and to test the reliability of previously reported associations between eating tasty foods to cope and BMI. BMI, demographics, and scores on the PEMS and the Binge Eating Scale were obtained from 192 college students. Test-retest analysis was performed on the PEMS motives in groups varying in three gap times between tests. Regression analyses determined what PEMS motives predicted a change in BMI over two years. The results replicated previous findings that eating palatable food for Coping motives (e.g., to forget about problems, reduce negative feelings) is associated with BMI. Test-retest correlations revealed that motive scores, while somewhat stable, can change over time. Importantly, among overweight participants, a change in Coping scores predicted a change in BMI over 2 years, such that a 1-point change in Coping predicted a 1.76 change in BMI (equivalent to a 10.5 lb. change in body weight) independent of age, sex, ethnicity, and initial binge-eating status (Cohens f(2) effect size = 1.44). The large range in change of Coping scores suggests it is possible to decrease frequency of eating to cope by more than 1 scale point to achieve weight losses greater than 10 lbs. in young overweight adults, a group already at risk for rapid weight gain. Hence, treatments aimed specifically at reducing palatable food intake for coping reasons vs. for social, reward, or conformity reasons, should help achieve a healthier body weight and prevent obesity if this motive-type is identified prior to significant weight gain.

Cooling rate effect upon the field‐cooled magnetization of an insulating spin‐glass

The field‐cooled magnetization (FCM) of two cobalt aluminosilicate spin‐glasses have been measured as a function of applied magnetic field and the rate of cooling through the spin‐glass freezing temperature, Tf. For the lowest fields, a difference of ∼5% in the magnitude of the FCM for T<Tf was observed between the fastest cooling rate of ≳200 mK/s and the slowest rate of 1 mK/s. The magnitude of the FCM at a constant T<Tf did not change over a period of 8×104 s; and as long as the warming rate was the same as the cooling rate, the FCM was essentially ‘‘reversible.’’ These cooling rate effects show striking similarity to a real liquid‐glass transition and suggest the FCM ‘‘plateau’’ may arise from the cooling rate being faster than the time necessary for the magnetic spins to relax to their true thermodynamic equilibrium.

Magnetic properties of nanosized iron oxide particles precipitated in alginate hydrogels

Nanoparticles of γ-Fe2O3 (size 2–3nm) were precipitated in alginate hydrogels by cross-linking sodium alginate with Fe ions in a methanol-water solution. The zero-field-cooled and field-cooled magnetization measurements between 5 and 350K and the hysteresis in the M vs H relation below the blocking temperature indicate superparamagnetic behavior. The temperature dependence of the coercive field is not consistent with the T1∕2 behavior predicted by Neel and Brown for the noninteracting particles. The average diameter of the nanoparticles determined from the magnetic data is consistently larger than the corresponding particle size determined by x-ray diffraction, perhaps due to interparticle magnetic interactions.

Real-time sampling of reasons for hedonic food consumption: further validation of the Palatable Eating Motives Scale

Highly palatable foods play a salient role in obesity and binge-eating, and if habitually eaten to deal with intrinsic and extrinsic factors unrelated to metabolic need, may compromise adaptive coping and interpersonal skills. This study used event sampling methodology (ESM) to examine whether individuals who report eating palatable foods primarily to cope, to enhance reward, to be social, or to conform, as measured by the Palatable Eating Motives Scale (PEMS), actually eat these foods primarily for the motive(s) they report on the PEMS. Secondly this study examined if the previously reported ability of the PEMS Coping motive to predict BMI would replicate if the real-time (ESM-reported) coping motive was used to predict BMI. A total of 1691 palatable eating events were collected from 169 college students over 4 days. Each event included the day, time, and types of tasty foods or drinks consumed followed by a survey that included an abbreviated version of the PEMS, hunger as an additional possible motive, and a question assessing general perceived stress during the eating event. Two-levels mixed modeling confirmed that ESM-reported motives correlated most strongly with their respective PEMS motives and that all were negatively associated with eating for hunger. While stress surrounding the eating event was strongly associated with the ESM-coping motive, its inclusion in the model as a predictor of this motive did not abolish the significant association between ESM and PEMS Coping scores. Regression models confirmed that scores on the ESM-coping motive predicted BMI. These findings provide ecological validity for the PEMS to identify true-to-life motives for consuming palatable foods. This further adds to the utility of the PEMS in individualizing, and hence improving, treatment strategies for obesity, binge-eating, dietary nutrition, coping, reward acquisition, and psychosocial skills.

Memory effects and magnetic interactions in a γ‐Fe2O3 nanoparticle system

The low-temperature dynamics of a magnetic nanoparticle system (γ‐Fe2O3—alginate nanocomposite with average particle size around 4nm) have been studied by superconducting quantum interference device measurements. Using different temperature and field protocols, memory phenomena in the dc magnetization and magnetic relaxation have been observed at temperatures below its blocking temperature TB=37K. However, aging experiments show an absence of any waiting time dependence in the magnetization relaxation. These observations indicate that the dynamics of this nanoparticle system are governed by a wide distribution of particle relaxation times which arise from the distribution of particle sizes and weak interparticle interactions.