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The Li–Mg–N–H system has been identified as a promising hydrogen storage material due to its moderate operation conditions as well as the high capacity and reversibility. Recently Rijssenbeek et al. [J. Alloys Compd. 454, 233 (2008)] reported that Li2Mg(NH)2 has disordered cation and vacancy arrangements at room temperature and above. We present our first-principles calculations to investigate a series of ordered low-energy configurations for this compound. Specific local orderings are found in the cation-vacancy arrangement, shedding light on the experimental disordered structure models. A possible ordered phase at low temperature is proposed based on these local orderings. Reaction energetics and phase stability are further discussed. [ABSTRACT FROM AUTHOR]

The Li–Mg–N–H system has been identified as a promising hydrogen storage material due to its moderate operation conditions as well as the high capacity and reversibility. Recently Rijssenbeek et al. [J. Alloys Compd. 454, 233 (2008)] reported that Li2Mg(NH)2 has disordered cation and vacancy arrangements at room temperature and above. We present our first-principles calculations to investigate a series of ordered low-energy configurations for this compound. Specific local orderings are found in the cation-vacancy arrangement, shedding light on the experimental disordered structure models. A possible ordered phase at low temperature is proposed based on these local orderings. Reaction energetics and phase stability are further discussed. [ABSTRACT FROM AUTHOR]

The electronic and magnetic properties of Co-doped ZnO are investigated based on the B3LYP hybrid spin-density functional method. The calculated electronic structures obtained from B3LYP agree well with the experimental results. B3LYP predicts that antiferromagnetic (AFM) ordering between the Co ions is favored over ferromagnetic (FM) ordering in intrinsic Co-doped ZnO, and reveals that the FM ordering can be induced by electron doping when the doping level reaches 1 electron per Co ion. These results agree well with the FM ordering observed in highly conductive n-type Zn1-xCoxO films. Charge transfer to the minority-spin d states of Co atoms and the consequent double-exchange interaction are the primary origins of FM ordering. Since Ni has one more electron than Co, we also investigate the electronic and magnetic properties of intrinsic Ni-doped ZnO. Qualitatively different from the local-density-approximation results, B3LYP predicts that Ni-doped ZnO is an insulator and favors AFM ordering. [ABSTRACT FROM AUTHOR]

We investigate the formation of compositional modulation and atomic ordering in InGaP films. Such bulk properties—as well as surface morphologies—present a strong dependence on growth parameters, mainly the V/III ratio. Our results indicate the importance of surface diffusion and, particularly, surface reconstruction for these processes. Most importantly from the application point of view, we show that the compositional modulation is not necessarily coupled to the surface instabilities, so that smooth InGaP films with periodic compositional variation could be obtained. This opens a new route for the generation of templates for quantum dot positioning and three-dimensional arrays of nanostructures. [ABSTRACT FROM AUTHOR]

We report the microstructural evolution during irradiation of FePt and FePt 25 at. % thin films sputter deposited onto electron transparent silicon monoxide substrates. The films were studied in situ for 500 keV Kr+ irradiation up to a fluence of 1015 ions/cm2 or 4 displacements/atom (dpa). Upon irradiation to approximately 1 dpa, the initial disconnected granular morphology became continuous. In particular, for FePt, accelerated grain growth was observed once the continuous morphology was achieved during ambient temperature irradiation. No atomistic (chemical) ordering from the as-deposited A1 phase into either the L10 FePt or L12 Fe3Pt phases was observed during ambient temperature irradiation. After irradiation, the specimens were then in situ annealed. The intermetallic ordering temperature, compared to that of an unirradiated film, was lowered by ≈200 °C for FePt 25 at. %. No decrease in the ordering temperature was observed for irradiated FePt. The rate of FePt grain growth during annealing was very similar for both irradiated and unirradiated films over the 25–650 °C temperature range investigated. [ABSTRACT FROM AUTHOR]

Fe-Ga alloys with compositions near 27.5 at. % Ga (26-29 at. %) can be heat treated to obtain ordered phases based on &alpah;″ (ordered bcc), D0[SUB19] (ordered hexagonal), and L1[SUB2] (ordered fcc) structures. This work presents an evaluation of how the different ordering treatments influence the magnetostriction in cast polycrystalline Fe-27.5 at. % Ga alloy. Alloy samples were annealed first in the disordered bcc (A2) phase region to obtain a disordered bcc solid solution, followed by ordering-heat treatment in the appropriate temperature region of stability of each of the ordered phases. X-ray diffraction was used to characterize the phases present prior to and after heat treatments. Magnetostriction measurements were carried out at different prestress levels in the range of 0-50 MPa. Magnetic properties were measured using a vibrating sample magnetometer. Annealed Fe-27.5 at. % Ga sample with a disordered bcc (A2) structure and a weak [110] texture showed a magnetostriction value of 115 × 10[SUP-6]. The α″ ordering treatment resulted in a small decrease of saturation magnetostriction. Magnetostriction decreased to negligible or small negative levels after D0[SUB19] and L1[SUB2] ordering treatments. [ABSTRACT FROM AUTHOR]

The optical properties of the ordered defect compound CuIn[sub 5]Se[sub 8], which crystallizes in a hexagonal structure, have been studied by the absorption technique. The analysis of the data shows that the band gap energy E[sub G] varies from 1.23 to 1.13 eV between 10 and 300 K. It is found that the variation of E[sub G] with temperature is due to the contribution of both acoustic and optical phonons with a characteristic phonon energy of about 14 meV. The optical absorption coefficient just below the absorption edge varies exponentially with photon energy indicating the presence of Urbach’s tail. The phonon energy hν[sub p] associated with Urbach’s tail, which is found to be 53 meV, is higher than the highest optical phonon mode reported for this compound, which is about 29 meV. The origin of the additional energy is attributed to the contribution of localized modes produced by structural disorder of low energy formation. An empirical relation, also used earlier in the case of 1:1:2 and other ordered defect compounds of the 1:3:5 phases, explains very well the variation of Urbach’s energy with temperature. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which examined the ordering and stability of lead[sub 1-x]europium[sub x]tellerium alloys. Use of transmission electron microscopy; Experimental details; Results and discussion.

Presents a study which examined the consequences for magnetism of icosahedral site symmetry and of long-range icosahedral ordering as found in quasicrystals. Factors that were predicted for long-range icosahedrally ordered magnets; Description of icosahedral quasicrystals; Reason for using the term quasicrystals; Examples of crystal structures that exist with local icosahedral structural units.

Examines γ-Fe[sub2]-O[sub3] particles by convergent beam electron diffraction to determine the crystal symmetry. Commercial samples obtained; Occurrence of order-disorder transition.

Reports on the effect of order-disorder transition on magnetic properties of high silicon-iron single crystals. Method used to make high-silicon single crystals; Way that can change the saturation magnetization, the magnetocrystalline anisotropy constant and the saturation magnetostriction constants in such crystals; Factor to which the phenomena is attributable.

Investigates the effects of growth rate on the step structure and ordering in gallium-indium-potassium (GaInP) epitaxial layers. Formation of copper-platinum (CuPt) ordering during epitaxial growth; Atomic-scale physical processes occurring on the surface; Correlation between step structure and ordering.

Presents information on a study which used surface photoabsorption measurements to clarify the copper-platinum ordering mechanism in Ga[sub0.5]In[sub0.5]P layers grown by organometallic vapor phase epitaxy. Methodology of the study; Results and discussion on the study; Conclusions.

Presents a study that investigated the effect of growth rate on step structure and ordering in gallium indium phosphide. Method of the study; Results and discussion; Conclusion.

We extend to a new antiferromagnetic alloy, IrMn, point-contact based studies of the effect of a large current density on the exchange bias at antiferromagnet/ferromagnet (AFM/F) interfaces. Similarly to the case of AFM=CoFe, a negative current density ∼1012 A/m2 injected through the F=CoFe into an IrMn/CoFe interface was found to increase the exchange bias, while a positive current decreased it. The model used to describe the data for FeMn/CoFe, based on predicted current-induced torques on AFM, can explain the new data. [ABSTRACT FROM AUTHOR]

In this paper we examine the elastic (c′ and c44) and magnetostrictive (λ100 and λ111) behaviors of Fe100-xGex for 4

Planar patterned media using CrPt3 ordered alloy films were fabricated by Ar+ or Kr+ ion irradiation through nanoimprinted or electron beam lithography made masks. CrPt3 ordered alloy film on fused quartz substrate exhibits a large perpendicular anisotropy of 5×106 erg/cc and a large coercivity of 12 kOe, and we found that its magnetic order (magnetization) was completely suppressed by a quite low Ar+ or Kr+ ion dose of about 1–2×1014 ions/cm2. Magnetic force microscope image of the ion-beam patterned CrPt3 with a bit size of 90×90 nm showed clear magnetic contrast in nonirradiated regions, while no magnetic contrast in irradiated regions. The read-back waveform taken from an ion-beam patterned CrPt3 disk with 600 nm patterning pitch showed sharp signal transition between irradiated and nonirradiated regions, which indicates the possibility of high-density planar patterned media using CrPt3 ordered alloy. [ABSTRACT FROM AUTHOR]

The order-disorder transition produced by ball milling in the intermetallic Fe[SUB70]Al[SUB30] has been systematically studied by x-ray diffraction, calorimetry, and Mössbauer experiments. These techniques show a monotonous transformation that ends after 6 h of milling. In the transition, the lattice parameter increase amounts to 0.7% and there is a large enhancement of the alloy's magnetism. [ABSTRACT FROM AUTHOR]

The combination of Mössbauer spectroscopy and magnetization measurements is demonstrated to be efficient in the determination of the phases responsible for the glassy magnetic dynamics of the highly disordered alloy Fe[sub 35]Al[sub 50]B[sub 15] produced by mechanical alloying. Its spin-glass behavior is apparent from the FC-ZFC magnetization irreversibility, the thermoremanent magnetization, and the slightly frequency-dependent peak in the temperature dependence of the ac susceptibility. Furthermore, the maximum at T[sub p] ≈ 22 K in the real component of the ac susceptibility is accompanied by a sudden onset of the imaginary component. The fit of the frequency dependence of T[sub p] to the critical slowing down law yielded a critical exponent z v = 8 ± 1. However, Mössbauer spectroscopy uncovered the existence of two different Fe environments, of which only the minor one freezes at low temperatures into a distribution of magnetic sextets. This result, combined with the superparamagnetic behavior detected at moderate fields, allowed us to ascribe the spin glass behavior to the presence of interacting, very fine, ferromagnetic clusters (estimated size ∼ 1 nm). The origin of this nanoscale compositional heterogeneity is argued to be related to regions of partially unalloyed Fe. The conclusions are contrasted with other mechanically alloyed systems with reported spin glass behavior or compositional inhomogeneity. [ABSTRACT FROM AUTHOR]

Magnetization vs temperature behavior of RuSr[sub 2]GdCu[sub 2]O[sub 8-δ] (Ru-1212) measured in an field of 5 Oe, shows a clear branching of zero-field-cooled (ZFC) and field-cooled (FC) curves around 140 K, a cusp at 135 K, and a diamagnetic transition around 20 K (in the ZFC branch). The cusp at 135 K is due to the antiferromagnetic ordering of the Ru moments. The magnetization-field isotherms, below 50 K, show a nonlinear contribution from a ferromagnetic component. The resistance vs temperature behavior of the compound, in applied fields of 0, 3, and 7 T, confirms that the sample is superconducting at around 20 K. The superconducting transition exhibits field broadening of a type different than that known for conventional high T[sub c] superconductors. The magnetoresistance (MR) is negative above the Ru magnetic ordering temperature of 135 K, while below this temperature, MR displays a positive peak in low fields and becomes negative in higher fields. A maximum of 2% is observed for the negative MR value at the Ru magnetic ordering temperature. An electron diffraction pattern obtained for this Ru-1212 sample shows two types of superstructure; one with a weak spot at the center of the a-b rectangle and the other only along the b direction. It is possible that either Ru/Cu or Ru[sup 4+] / Ru[sup 5+] ordering of 2b periodicity takes place along the b direction. [ABSTRACT FROM AUTHOR]

Atomic ordering, nanostructure and the magnetic properties of polycrystalline FePdPt thin films deposited with MgO underlayers have been investigated. The film thickness was fixed at 5 nm in all films, a thickness where perpendicular anisotropy is dominant. Films deposited at ambient temperature were postannealed at various temperatures to study the kinetics of atomic ordering. The Pd additions to FePt were effective in reducing the temperature needed for atomic ordering. The mean grain size determined by transmission electron microscopy is about 10 nm in annealed films. Within the limits of our observations, FePdPt films do not show phase separation into more than one phase of the L 10 structure. The maximum coercivity (H[sub c]) for annealed FePdPt films is about ∼3000-4000 Oe. In situ ordered FePdPt films at 530 °C show no indication of a lower temperature for atomic ordering. [ABSTRACT FROM AUTHOR]

The influences of random disorder in the barrier on tunnel conductance (TC) and magnetoresistance (TMR) in ferromagnet (FM)/insulator (semiconductor) (I(S))/FM junctions are investigated theoretically taking into account spin-orbit (SO) interaction. The TMR decreases significantly due to the spin-flip scattering (SF) caused by the SO interaction. We have found that the SF scattering is much stronger for anti-parallel configuration of magnetization and the TMR can even be inverted when the SF scattering is beyond some critical value. The numerical calculations are performed within the single-orbital tight-binding model using the recursive Green's function method based on the extended Landauer-Bfittiker formula. [ABSTRACT FROM AUTHOR]

Current–voltage (I–V) characteristics of Pr[sub 0.5]Sr[sub 0.3]Ca[sub 0.2]MnO[sub 3] are measured at different temperatures and different fields. Our data of I–V curves show a crossover from linear to nonlinear behavior at the temperature lower than the charge ordering temperature. New findings in this work include (i) abrupt jumps/drops of voltage in each I–V curve below 100 K and (ii) an enhancement of magnetoresistance (MR) ratio from 15% to 20% which is associated with the unusual voltage jumps/drops in I–V curves. The enhancement of MR ratio evidences the existence of an intermediate state between the charge ordering state and the charge ordering breakdown state. Most importantly, the existence of such intermediate state provides a new route to achieve a low field colossal magnetoresistance for future applications of spintronics. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Single crystals of R[sub 1/3]Sr[sub 2/3]FeO[sub 3] (R=Pr, Nd, and Sm) were synthesized by the floating zone method and their magnetic properties and charge ordering (CO) transition related to lattice dynamics were systematically investigated. Mo¨ssbauer spectra of R[sub 1/3]Sr[sub 2/3]FeO[sub 3] were taken at various temperatures ranging from 12 K to room temperature. The charge disproportionation in Pr[sub 1/3]Sr[sub 2/3]FeO[sub 3] was detected below 190 K, in which two kinds of iron with valence states Fe[sup 3+] and Fe[sup 5+] were found with ratio of 2:1. The iron with valence state Fe[sup 4+] in Pr[sub 1/3]Sr[sub 2/3]FeO[sub 3] coexists at and above 150 K, and its ratio increased from 13% to 66% as the temperature rose. The (Nd[sub 1-y]Sm[sub y])[sub 1/3]Sr[sub 2/3]FeO[sub 3] (y=0.0, 0.2, 0.4, 0.6, and 0.8) with least lattice distortion underwent a CO phase transition at and below T[sub CO]=163 K and accompanying the charge disproportionation into nominally Fe[sup 3+] and Fe[sup 5+] sites as well as a canted antiferromagnetic spin ordering. In this charge ordering state, a sequence of Fe[sup +3]Fe[sup +3]Fe[sup +5]Fe[sup +3]Fe[sup +3]Fe[sup +5] exists aligned along the [111] direction of the pseudocubic perovskite structure. In this study, the CO at x=2/3 disappeared in the case of R=Sm. Indeed, disappearance of the CO transition was detected by systematic decrease of a spontaneous magnetization with increase of y in the system of (Nd[sub 1-y]Sm[sub y])[sub 1/3]Sr[sub 2/3]FeO[sub 3]. This result shows that the charge ordering state was realized with strong hybridization between the Fe and O atoms. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The magnetic ordering in the series of transition metal alloys (Fe[sub 1-x]T[sub x])[sub 3]Ga[sub 4] with T=Ni and Ti having values of x in the range 0.05≤x≤0.20 has been investigated at high fields and low temperatures. Magnetization measurements revealed that in contrast to other T substitutions, Ni and Ti induce completely different types of effects on the magnetic properties. In the case of Ni substitution a ferrimagnetic-like type of magnetic order is induced at low compositions and low temperatures and Ti produces a ferromagnetic ground state. For Ti alloys with low composition as the temperature is increased a field induced transition starts to appear at about 50 K which persists up to room temperature suggesting a phase transition from a ferromagnetic to an antiferromagnetic state. The phase diagrams of the Ni and Ti system are explainable in terms of the Moriya-Usami and Isoda theories. Preliminary neutron diffraction measurements on the Ni alloys carried out at ILL suggest the existence of short-range order over a certain temperature range. The behavior observed so far on the various substituted systems leads us to believe that there is a clear relation between the magnetic properties and the relative position of the substitution element with respect to Fe in the Periodic Table. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Rapidly solidified Sm[sub 11]Fe[sub 89] was observed to form partially ordered Sm[sub 2]Fe[sub 17]. The ordering increased systematically with annealing temperature, reaching an order parameter of 0.8 after annealing at 950 °C for 15 min. The coercivity of the corresponding interstitial compound Sm[sub 2]Fe[sub 17]N[sub x] varied with annealing temperature and thus order parameter. The coercivity reached a maximum for an order parameter of 0.45–5, then dramatically decreased as the order increased. This behavior is characteristic of demagnetization controlled by domain wall pinning by antiphase boundaries. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on a study that examined the behaviors of ordering and disordering in binary iron-aluminum thin films. Manner of examining Fe[sub3]Al films; Composition of the films.

Presents a study which examined the oxygen dependence of the magnetic order of neodymium in neodymium barium[sub2]copper[sub3]oxygen[sub6+x]. Details of neutron scattering experiments; Discussion of specific heat measurements; Results.

Discusses a study which examined the short-ordering of frustrated magnet compound Tb[sub2]Mo[sub2]O[sub7]. Structure of the magnetic compound; Determination of the nature of magnetic ordering in the compound; Analysis of small-angle neutron scattering.

Presents a study which examined the quenching of ferrimagnetic-like ordering in strontium chromium[sub8]iron[sub4]oxygen[sub19] hexagonal ferrite. Experimental procedure; Results; discussion.

Presents a study which examined the magnetic states of disordered nickel-manganese alloys under hydrostatic pressure. Measurement of low-field alternating current susceptibility of disordered nickel-manganese alloys; Experimental procedure and data; Results and discussion.

Investigates the magnetic ordering in YGd alloys. Description of the low-field susceptibility; Confirmation of the existencde of a long-range ordering; Analysis of the antiferromagneticlike properties of the YGd alloys.

Presents an abstract of the paper `Magnetic Ordering and Magnetic Excitations in the Induced Moment Distorted Triangular Antiferromagnet TlFeCl3 Under Hydrostatic Pressure,' presented by A.R. Monteith, D. Pettigrand, et al, at the American Institute of Physics' 1997 Conference on Magnetism and Magnetic Materials.

Presents the abstract of the study by Visser about the neutron scattering examination of the magnetic ordering in triangular antiferromagnets.