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We have grown several single crystals of the highly frustrated $S$ = 1 spinel MgV${}_{2}$O${}_{4}$ using different starting compositions and growth conditions. From our study of their physical properties by magnetic susceptibility, heat capacity, and single-crystal neutron and powder-diffraction measurements, we observe that a minute amount of disorder suppresses the structural and magnetic phase transitions. As little as 3$%$ disorder in the octahedral site introduced random strain, which was enough to completely suppress the transitions and induce a spin-glass phase at low temperatures. We believe that the reason is spin-exchange disorder rather than disorder in the weakly diluted magnetic lattice. Our results also show that the MgO-V${}_{2}$O${}_{3}$ system is a solid solution that melts slightly incongruently, and we demonstrate that by using an optimized solvent in the traveling-solvent floating-zone configuration a large single crystal ($l$ = 25 mm, $d$ = 6 mm) with a homogeneous composition, free of site disorders can be grown.

The temperature dependence of the hyperfine parameters of thulium iron garnet (Tm3Fe5O12) powder was studied from 90 to 550 K using169Tm and57Fe Mossbauer spectroscopy (MB). The spectra were analyzed by least mean square fits to the transmission function. The temperature dependence of the magnetic fields of the thulium nuclei is well described by the mean field model. The coupling constants between the magnetic lattice occupied by the thulium atoms and the magnetic lattices occupied by the iron atoms were derived.

The anisotropic triangular lattice of the crednerite system Cu(Mn$$_{1-x}$$Cu$$_{x}$$)O$$_{2}$$ is used as a basic model for studying the influence of spin disorder on the ground state properties of a two-dimensional frustrated antiferromagnet. Neutron diffraction measurements show that the undoped phase (x=0) undergoes a transition to antiferromagnetic long-range order that is stabilized by a frustration-relieving structural distortion. Small deviation from the stoichiometric composition alters the magnetoelastic characteristics and reduces the effective dimensionality of the magnetic lattice. Upon increasing the doping level, the interlayer coupling changes from antiferromagnetic to ferromagnetic, while the structural distortion is fully suppressed. Concomitantly, the long-range magnetic order is gradually transformed into a two-dimensional order.

Using Monte Carlo simulations and finite-size scaling, we investigate the critical behavior of two-dimensional magnetic lattice gas at densities rho = 0.90, 0.95, 1.0. There is a ferromagnetic phase transition at each density. As expected, the critical temperature T-c depends on system density rho. Unexpectedly, there is a density dependence of the critical exponent of correlation length v. For densities rho = 0.90, 0.95, 1.0, we obtain the inverse of critical exponent 1/v = 0.835(5), 0.905(5), 1.00(1) respectively. It is found that the ratios of critical exponent beta/v and gamma/v of magnetization and susceptibility are independent of density.

Following the advent of laser cooling and trapping techniques in the 1980s, a new exciting area of research, ‘atom chips’, has emerged in which sophisticated micronscale structures on planar substrates are produced utilizing the latest technological developments in lithography and nanofabrication. These complex microstructures produce tiny magnetic field configurations which can trap, cool, and manipulate ensembles of ultra-cold atoms in the vicinity of a surface. Scaling down the dimensions of atom trapping geometry offers extended possibilities for the production and control of Bose–Einstein condensates (BECs). Enormous progress on the generation of BECs and quantum degenerate Fermi gases, on-chip matter–wave interferometers, and integrated detectors has been made in the last few years. In the second section of this article we trace the historical evolution of this new field, from the first surface-based atom optical elements –magneticmirrors – to the present-day micro-fabricated structures on a substrate – atom chips. In Section 1.3 we present the basic principles of magnetic mirrors for cold atoms and describe different types of magnetic mirror. Section 1.4 describes the production of a BEC on a permanent magnetic film atom chip; the application of this atom chip to probe the topology of magnetic fields using RF spectroscopy and to study the adiabatic splitting of a BEC in a double well for sensing asymmetric potentials; and investigations of the spatially dependent relative phase evolution of a two-component BEC. Finally, in Section 1.5 we describe a permanent magnetic lattice on an atom chip for trapping and manipulating multiple arrays of ultra-cold atoms and quantum degenerate gases.

Double perovskites of the form A_2BB'O_6 usually involve a transition metal ion, B, with a large magnetic moment, and a non magnetic ion B'. While many double perovskites are ferromagnetic, studies on the underlying model reveal the possibility of antiferromagnetic phases as well driven by electron delocalisation. In this paper we present a comprehensive study of the magnetic ground state and T_c scales of the minimal double perovskite model in three dimensions using a combination of spin-fermion Monte Carlo and variational calculations. In contrast to two dimensions, where the effective magnetic lattice is bipartite, three dimensions involves a geometrically frustrated face centered cubic (FCC) lattice. This promotes non-collinear spiral states and `flux' like phases in addition to collinear anti-ferromagnetic order. We map out the possible magnetic phases for varying electron density, `level separation' epsilon_B - epsilon_B', and the crucial B'-B' (next neighbour) hopping t'., Comment: 15 pages pdflatex + 19 figs, revision: removed redundant comments

The paper describes the transport of the elastically and diffractively scattered protons in the proton-proton interactions at the LHC for the high beta* runs. A parametrisation of the attered proton transport through the LHC magnetic lattice is presented. The accuracy of the unfolding of the kinematic variables of the scattered protons is discussed., Comment: 12 pages, 15 figures

Following the discovery of organic ferromagnetism in p-NPNN, we report the observation of ferromagnetic ordering in a second nitronyl nitroxide radical system, 3-quinoyl nitroxide (3-QNNN), using the muon spin rotation (MUSR) technique. The onset of ferromagnetic order is indicated in the MUSR experiment by the appearance of a rotation signal in zero applied field for temperatures below ∼0.2 K. This signal corresponds to the precession of the muon spin in the internal field of the ferromagnetic state. We have measured the muon spin rotation and relaxation signals as a function of temperature, giving a measure of the magnetization and spin dynamical properties. The temperature dependence of the internal field is consistent with the S = 12 Weiss molecular field model with a Curie temperature of 0.21 K and a saturation internal field of 60 G. We also report additional studies of the magnetic properties of 3-QNNN and p-NPNN using EPR and a.c. susceptibility techniques. We find evidence for a canted ferromagnetic spin structure in 3-QNNN and a simpler uniform magnetic lattice in p-NPNN.

A magnetic gap soliton theory for the intrinsic self-localized magnon modes in one-dimensional Heisenberg antiferromagnets is developed in this paper. It is shown that these solitons have zero group velocity in the magnetic lattice and that the frequency of carrier wave is within the gap of magnon band. Different from the results obtained recently by lattice Green's function, our approach demonstrates that only the antisymmetric two-spin bound state can exist. We also show that the system can produce a new type of intrinsic self-localized magnon mode, a nonpropagating kink, whose oscillatory frequency is just below the upper cut-off of the magnon band.

Typical molecular-based magnets, decamethylferrocenium tetracyanoethenide ([DMeFc][TCNE]) and decamethylferrocenium tetracyanoquinodimethanide ([DMeFc][TCNQ]), have been studied by means of adiabatic calorimetry. The Curie temperature of [DMeFc][TCNE] was determined to be Tc - 4.74 K. The excess entropy derived from the observed heat-capacity anomaly was very close to the expected magnetic entropy, 2 R In 2. Detailed analysis of the heat-capacity anomaly revealed that [DMeFc][TCNE] is a good one-dimensional (ID) Ising magnet. Two structural phase transitions were found for the first time at 248.7 and 281.8 K, and attributed to the orientational order-disorder character of the TCNE anion. For [DMeFc][TCNQ] an antiferromagnetic phase transition was observed at TN = 2.54 K. The magnetic lattice anisotropy of the TCNQ salt is smaller than that of the TCNE salt.

A model for real space singlet pairs (RSP), hopping on the quasi 2D antiferromagnetic background of localized spins, is presented. It is found that the “gas parameter” of the RSP's reaches unity at low enough temperatures, however small the concentration of RSP's. This happens due to the local coupling of the RSP to the growing antiferromagnetic fluctuations in the 2D magnetic layers. The low temperature increase of the magnetic correlation length ξ is suppressed significantly by the low energy density fluctuations in the quasi 2D RSP system, which develop already far above the Bose condensation temperature T c . The effective “magnetic mass” of the RSP is found to be proportional to (In ξ/ a ) 2 , where a is the magnetic lattice spacing. Both the magnetic energy shift and the size of the “magnetic cloud” of the RSP are calculated. The results are applied to the explanation of the NMR behavior observed in the high- T c cuprates.

An atom moving in a spatially periodic field experiences a temporary periodic perturbation and undergoes a resonance transition between atomic internal states when the transition frequency is equal to the atomic velocity divided by the field period. We demonstrated that spin nutation was induced by this resonant transition in a polarized rubidium (Rb) atomic beam passing through a magnetic lattice. The lattice was produced by current flowing through an array of parallel wires crossing the beam. This array structure, reminiscent of a multiwire chamber for particle detection, allowed the Rb beam to pass through the lattice at a variety of incident angles. The dephasing of spin nutation was reduced by varying the incident angle., Comment: 11 pages, 4 figures, submitted to Phys. Rev. A

For ${\text{Sm}}^{3+}$ ions in a vast majority of metallic systems, the following interesting scenario has been conjured up for long, namely, a magnetic lattice of tiny self- (spin-orbital) compensated $4f$-moments exchange coupled (and phase reversed) to the polarization in the conduction band. We report here the identification of a self-compensation behavior in a variety of ferromagnetic Sm intermetallics via the fingerprint of a shift in the magnetic hysteresis $(M\text{\ensuremath{-}}H)$ loop from the origin. Such an attribute, designated as exchange bias in the context of ferromagnetic/antiferromagnetic multilayers, accords these compounds a potential for niche applications in spintronics. We also present results on magnetic compensation behavior on small Gd doping $(2.5\text{ }\text{at}\text{.}\text{ }\mathrm{%})$ in one of the Sm ferromagnets (viz., ${\text{SmCu}}_{4}\text{Pd}$). The doped system responds like a pseudoferrimagnet and it displays a characteristic left-shifted linear $M\text{\ensuremath{-}}H$ plot for an antiferromagnet.

A survey of the crystal structures of materials that are currently being studied in the context of geometric magnetic frustration in triangular lattices is presented, based on a purely geometrical picture of their magnetic lattices. Two-dimensional materials are first described, followed by three dimensional materials of increasing structural complexity. When known, both transition metal and rare earth based examples within a lattice type are noted. The ideal cases are described, as well as the geometries that are found in some materials for which ideal triangular symmetry is broken in different ways. A brief description of materials preparation and crystal growth is also presented.

To shed light on the role of magnetism on the superconducting mechanism of the oxygen-free FeAs pnictides, we investigate the effect of magnetic ordering on phonon dynamics in the low-temperature orthorhombic parent compounds, which present a spin density wave. The study covers both the 122 (AFe(2)As(2); A = Ca, Sr, Ba) and 1111 (AFeAsF; A = Ca, Sr) phases. We extend our recent work on the Ca (122 and 1111) and Ba (122) cases by treating, computationally and experimentally, the 122 and 1111 Sr compounds. The effect of magnetic ordering is investigated through detailed non-magnetic and magnetic lattice dynamical calculations. The comparison of the experimental and calculated phonon spectra shows that the magnetic interactions/ordering have to be included in order to reproduce well the measured density of states. This highlights a spin-correlated phonon behavior which is more pronounced than the apparently weak electron-phonon coupling estimated in these materials. Furthermore, there is no noticeable difference between phonon spectra of the 122 Ba and Sr, whereas there are substantial differences when comparing these to CaFe(2)As(2) originating from different aspects of structure and bonding.

Three CeNi x Sn 2 compounds of different nominal Ni concentrations ( x = 0.65, 0.75, 0.85) were studied by high resolution neutron diffraction. The refinement of the nuclear structure shows that these compounds are single phase and that the actual compositions are close to the nominal ones. Low temperature neutron data of the CeNi 0.85 Sn 2 compound [refined to x = 0.864(2)] confirm the mictomagnetic behaviour already observed in a previous sample ( I ) refined to x = 0.840(4): coexistence of domains of two distinct magnetic phases in equal amounts. The relative amount of the two domains depends on x . One of these phases is ferromagnetic, q 1 = 0 with T C = 3 K. The other phase is a modulated antiferromagnet (antiphase domain type with two amplitudes) with T N = 4.0 K . Its magnetic ordering can be described by two propagation vectors q 2 = (010) ( C p magnetic lattice) and q 3 = 1 3 b ∗ . The ordered magnetic moment valueat 1.5 K in both phases is 2.0 μ B /Ce atom and the moments point into the same direction, along c. In sample ( I ) the two phases were present in equal amounts while in the present sample the amount of the ferromagnetic phase is strongly reduced to approximately 16%. The magnetic properties of these compounds and of compounds with higher and lower nominal Ni concentrations have been studied by us in more detail by means of measurements of specific heat, the magnetisation, the AC and DC susceptibility. In several cases two magnetic phase transitions were observed. The nature of these transitions is discussed in the light of the low-temperature neutron diffraction results obtained for the more Ni-rich samples.

The crystal and magnetic structures of the S=3/2 antiferromagnet β-CaCr2O4 have been investigated by means of specific heat, magnetization, muon relaxation, and neutron powder diffraction between 300 and 1.5 K. In this compound, in which the unusual topology of the Cr3+ magnetic lattice can be described as a network of triangular “zigzag” ladders with legs parallel to c, a complex antiferromagnetic ordering with an incommensurate propagation vector k=(0,0,q) (q∼0.477 at 1.5 K) is evidenced below TN=21 K. This complex magnetic ordering can be described as a honeycomblike arrangement of cycloids, running along c, and presenting a unique pattern of staggered chirality. To understand the experimental observation of this staggered chirality, we propose to use antisymmetric Dzyaloshinskii-Moriya terms in the exchange Hamiltonian.

Spin-frustrated systems are one avenue for inducing macroscopic quantum states in materials. However, experimental realization of this goal has been difficult because of the lack of simple materials and, if available, the separation of the unusual magnetic properties arising from exotic magnetic states from behavior associated with chemical disorder, such as site mixing. Here we report the synthesis and magnetic properties of a new series of magnetically frustrated materials, MgxCu4-x(OH)6Cl2. Because of the substantially different ligand-field chemistry of Mg2+ and Cu2+, site disorder within the kagom\'e layers is minimized, as directly measured by X-ray diffraction. Our results reveal that many of the properties of these materials and related systems are not due to disorder of the magnetic lattice but rather reflect an unusual ground state., Comment: Accepted for publication in J. Am. Chem. Soc.

We present neutron-scattering results on the magnetic excitations in the spinel compounds Lix[Mn1.96Li0.04]O4 (x=0.2,0.6,0.8,1.0). We show that the dominant excitations below T?70?K are determined by Mn ions located in clusters, and that these excitations mimic the dynamic scaling found in quantum critical systems that also harbor magnetic clusters, such as CeRu0.5Fe1.5Ge2. We argue that our results for this classical spinel compound suggest that the unusual response at low temperatures as observed in quantum critical systems that have been driven to criticality through substantial chemical doping is (at least) partially the result of the fragmentation of the magnetic lattice into smaller units.

We propose a new method to create an asymmetric two-dimensional magnetic lattice which exhibits magnetic band gap structure similar to semiconductor devices. The quantum device is assumed to host bound states of collective excitations formed in a magnetically trapped quantum degenerate gas of ultracold atoms such as a Bose-Einstein condensate (BEC) or a degenerate Fermi gas. A theoretical framework is established to describe possible realization of the exciton-Mott to discharging Josephson states oscillations in which the adiabatically controlled oscillations induce ac and dc Josephson atomic currents where this effect can be used to transfer n Josephson qubits across the asymmetric two-dimensional magnetic lattice. We consider second-quantized Hamiltonians to describe the Mott insulator state and the coherence of multiple tunneling between adjacent magnetic lattice sites where we derive the self consistent non-linear Schrodinger equation with a proper field operator to describe the exciton Mott quantum phase transition via the induced Josephson atomic current across the n magnetic bands.

Within a Kondo lattice, the strong hybridization between electrons localized in real space (r-space) and those delocalized in momentum-space (k-space) generates exotic electronic states called 'heavy fermions'. In URu2Si2 these effects begin at temperatures around 55K but they are suddenly altered by an unidentified electronic phase transition at To = 17.5 K. Whether this is conventional ordering of the k-space states, or a change in the hybridization of the r-space states at each U atom, is unknown. Here we use spectroscopic imaging scanning tunnelling microscopy (SI-STM) to image the evolution of URuSi2 electronic structure simultaneously in r-space and k-space. Above To, the 'Fano lattice' electronic structure predicted for Kondo screening of a magnetic lattice is revealed. Below To, a partial energy gap without any associated density-wave signatures emerges from this Fano lattice. Heavy-quasiparticle interference imaging within this gap reveals its cause as the rapid splitting below To of a light k-space band into two new heavy fermion bands. Thus, the URu2Si2 'hidden order' state emerges directly from the Fano lattice electronic structure and exhibits characteristics, not of a conventional density wave, but of sudden alterations in both the hybridization at each U atom and the associated heavy fermion states., Comment: Main Article + Supplementary Information

A method is presented for polarizing neutrons. It involves controlling both the total length and the ratio of the field strengths in a finite Fibonacci magnetic lattice compared with an infinite periodic magnetic lattice. Complete polarization is achieved if the lattice is sufficiently long which results in a finite operating window for the incident neutron energies. For a certain range of values of the controlling parameters in the Fibonacci magnetic lattice, both components of the dipole can be localized, thereby, constructing a neutron trap in this case.

The disordered magnetic lattice gas (DMLG) as a unifying description of many simpler random spin systems has been investigated in an attempt to devise a mean field theory which goes beyond the infinitely-long-ranged model by incorporating short-range order (SRO). The authors have shown rigorously that the local thermodynamic properties of the DMLG on a Cayley tree of finite coordination number z are identical to the thermodynamic properties of the DMLG in a pair approximation obtained by using the method of the distribution function. Further, a modified pair approximation for the DMLG is presented which is exactly solvable. It is formulated for general random bond distribution functions, and is then examined for the special case of Gaussian distributions.

CERN is preparing for the construction of the Large Hadron Collider (LHC) to be installed in the Large Electron Positron Collider (LEP) tunnel. The magnetic lattice of the LHC will consist of a ring of twin-aperture dipoles and quadrupoles, connected electrically in series. To adjust the working point of the machine, tuning quadrupoles will be installed in pairs in each regular cell, next to the main quadrupoles. Also, to correct multipolar field errors in the LHC, an octupole correction winding is required near each lattice quadrupole. A nested construction of these two magnets is foreseen. The design of a prototype tuning quadrupole and octupole corrector is described. Details of magnetic and mechanical calculations are given, including results from existing and specially developed computer codes, and model work. Further, the construction procedures are described, including the facilities and tooling developed by ACICA for this work. >

Three series of YBaCuOF powdered samples have been derived from the characteristic compositions O6 , O6.7 and O7 by a soft fluorination. The fluorine atoms occupy at first the O vacancies in the chains, then the bridging sites between the chains. 19 F NMR shows 4 types of lines corresponding respectively to a classical AF state, a very peculiar paramagnetic state in a large temperature range around TN with a very high local AF correlation. This structure is seen again in the superconducting samples and reveals an equilibrium between two magnetic structures at TC with slow magnetic fluctuations and lineshift. When put in the bridges, the F atoms seem to harden the magnetic lattice and push the sample out of the SC domain.

We propose a new method to realize a two-dimensional magnetic lattice, having two different configurations of asymmetric magnetic lattice, which exhibits magnetic band gap structure, and a symmetric magnetic lattice. We also describe the tunneling mechanisms of magnetically trapped ultracold atoms, prepared in a degenerate quantum gas such as Bose-Einstein Condensate (BEC). A coherent quantum tunneling of ultracold atoms between the sites of the asymmetrical magnetic lattice can be realized which induces the adiabatically controlled dc Josephson current. At critical phase transitions, namely at certain values of site phase difference and population fraction, a plasma oscillation can be observed in which it forms a discharging Josephson state to be used as coherently coupled n quantum bits.

An array of square current-carrying wires is proposed to construct a two-dimensional (2D) array of surface magneto-optical traps and Ioffe magnetic ones for realizing a 2D lattice of Bose-Einstein condensations (BECs) on an atom chip. Our study shows that when a vertical homogeneous bias magnetic field is only used, the wires will form a 2D array of quadrupole magnetic traps, which can be used to construct 2D lattice of surface magneto-optical micro-traps. While another horizontal homogeneous bias field is added simultaneously, the above 2D array of quadrupole micro-traps will be changed as an array of surface Ioffe micro-traps, which can be used to form a 2D magnetic lattice and then realize a 2D array of BECs. The dynamic loading process of cold (87)Rb atoms from each micro-MOT into Ioffe micro-trap is studied by using Monte-Carlo simulations, and our results show that the scheme can be used to realize a natural and effective loading of cold atoms from 2D array of micro-MOTs into 2D array of Ioffe micro-traps, and the loading efficiency can be reach ~ 65%. Moreover, the positions of each BEC (or MOT) in 2D array of magnetic micro-traps can be controlled by adjusting the currents in the wires or by changing the additional vertical bias field.

We report a $\ensuremath{\mu}\text{SR}$ study of ${\text{LiCrO}}_{2}$, which has a magnetic lattice made up of a stacking of triangular Heisenberg antiferromagnetic (${\text{Cr}}^{3+}$, $S=3/2$) layers. A static magnetically ordered state is observed below the transition temperature ${T}_{N}=62\text{ }\text{K}$, while the expected peak of the relaxation rate is slightly shifted downward by a few kelvins below ${T}_{N}$. We draw a comparison with the isostructural compound ${\text{NaCrO}}_{2}$, where an exotic broad fluctuating regime has been observed [A. Olariu, P. Mendels, F. Bert, B. G. Ueland, P. Schiffer, R. F. Berger, and R. J. Cava, Phys. Rev. Lett. 97, 167203 (2006)] and was suggested to originate from topological excitations of the triangular lattice. Replacing Na by Li strongly narrows the exotic fluctuating regime formerly observed in ${\text{NaCrO}}_{2}$, which we attribute to a more pronounced interplane coupling in ${\text{LiCrO}}_{2}$.

We report on an experimental study of the dynamics of the reflection of ultracold atoms from a periodic one-dimensional magnetic lattice potential. The magnetic lattice potential of period 10 {mu}m is generated by applying a uniform bias magnetic field to a microfabricated periodic structure on a silicon wafer coated with a multilayered TbGdFeCo/Cr magneto-optical film. The effective thickness of the magnetic film is about 960 nm. A detailed study of the profile of the reflected atoms as a function of externally induced periodic corrugation in the potential is described. The effect of angle of incidence is investigated in detail. The experimental observations are supported by numerical simulations.

We have formulated a relaxation mechanism for ferrites and ferromagnets (insulators and metals) whereby the coupling between the magnetic motion and lattice is based purely on continuum arguments concerning magnetostriction. This theoretical approach contrasts with previous mechanisms based on microscopic formulations of spin-phonon interactions employing a discrete lattice. Our model explains the scaling of the intrinsic ferromagnetic resonance linewidth with frequency, with temperature ${\ensuremath{\propto}1/{M}_{s}(T)}$ and the anisotropic nature of magnetic relaxation in ordered magnetic materials. Here, ${M}_{s}(T)$ is the thermal saturation magnetization. Without introducing adjustable parameters, our model is in reasonable quantitative agreement with experimental measurements of the intrinsic magnetic resonance linewidths of important class of ordered magnetic materials including both insulators and metals.

High resolution optical absoprtion spectra of the ion Er3+ (intrinsic or introduced as a probe) have been measured in cuprates R2Cu2O5 (R = Er, Lu, Y, Tb, Tm) related to high-Tc superconductors RBa2Cu3O7−x. Er3+ ground doublet splittings, magnetic transition temperatures, energies of crystal field levels for the ground multiplet of R have been determined. Splittings of spectral lines remain also at T >TN due to short-range order indicating the low-dimensional character of the copper magnetic lattice.

The MII and MIII magnetic ions in the extended molecular network P(C6D5)4MnFe(C2O4)3 form a two-dimensional honeycomb magnetic lattice. The Mn2+ and Fe3+ ions alternate in the extended network which is formed by the oxalate (C2O4) ligands. These hexagonal layers are separated and charge compensated by large [P(C6D5)4]+ ions, positioned in between the honeycomb layers. P(C6D5)4MnFe(C2O4)3 orders magnetically at TN=27(1) K. A full neutron spin polarization study of the neutron scattering cross section has been carried out which allows the unambigious separation of the magnetic cross section from the total diffraction process. The magnetic structure can be described with the magnetic Shubnikov group R3c. The magnetic moments are antiferromagnetically aligned along the c axis while the Mn2+ and Fe3+ ions form an antiferromagnetic alignment on the honeycomb lattice.

We introduce a diffusion model for energetically inhomogeneous systems. A random walker moves on a spin-S Ising configuration, which generates the energy landscape on the lattice through the nearest-neighbors interaction. The underlying energetic environment is also made dynamic by properly coupling the walker with the spin lattice. In fact, while the walker hops across nearest-neighbor sites, it can flip the pertaining spins, realizing a diffusive dynamics for the Ising system. As a result, the walk is biased towards high energy regions, namely the boundaries between clusters. Besides, the coupling introduced involves, with respect the ordinary diffusion laws, interesting corrections depending on either the temperature and the spin magnitude. In particular, they provide a further signature of the phase-transition occurring on the magnetic lattice.

We report on the loading and trapping of ultracold atoms in a one dimensional permanent magnetic lattice of period 10 micron produced on an atom chip. The grooved structure which generates the magnetic lattice potential is fabricated on a silicon substrate and coated with a perpendicularly magnetized multilayered TbGdFeCo/Cr film of effective thickness 960 nm. Ultracold atoms are evaporatively cooled in a Z-wire magnetic trap and then adiabatically transferred to the magnetic lattice potential by applying an appropriate bias field. Under our experimental conditions trap frequencies of up to 90 kHz in the magnetic lattice are measured and the atoms are trapped at a distance of less than 5 micron from the surface with a measured lifetime of about 450 ms. These results are important in the context of studies of quantum coherence of neutral atoms in periodic magnetic potentials on an atom chip., Comment: 10 Pages, 6 Figures

We summarize some mathematical methods used in the description of magnetic lattices for hadrons, based on the discrete formalism of symplectic maps. We first generalize the perturbative approach of normal forms to the resonant case; then we analyze the structure of the singularities of the conjugating function in the nonresonant case, making an analytic continuation of the perturbative series using Pade approximants. A nonperturbative method, which computes the invariants of the motion from the iterates of the map using a variational principle, is outlined. Two applications of the nonresonant normal forms to the physics of hadron accelerators are shortly discussed: the analysis of the dynamic aperture experiment carried out at the SPS in 1988 and the correction of the nonlinearities due to errors in the superconducting magnets in the LHC.

Co0.5Zn0.5FeCrO4 is typical of concentrated magnetic oxides which show characteristics of the spin glass phenomena in macroscopic measurements. AC susceptibility shows a broad peak at 147 K, spread over the temperature range from 90 to 170 K. Using Mossbauer spectroscopy, we show that the peak in the AC susceptibility is due to gradual conversion of the magnetic lattice into superparamagnetic clusters as the temperature increases, and spin arrangement at 4.2 K is of Yafet Kittel type.

A 1.2-GeV synchrotron light source is being constructed at the Center for Advanced Microstructures and Devices (CAMD) at Louisiana State University. The expressed purpose of the center, which has been funded by a grant from the US Department of Energy, is to develop X-ray lithography techniques for manufacturing microcircuits, although basic science programs are also being established. The storage ring will be optimized for the soft-X-ray region and will be the first commercially manufactured electron storage ring in the United States. The magnetic lattice is based on a design developed by Chasman and Green and will allow up to three insertion devices to be installed for higher-energy and higher-intensity radiation. In addition to the lithography effort, experimental programs are being established in physics, chemistry, and related areas.

We have realized a two dimensional permanent magnetic lattice of Ioffe-Pritchard microtraps for ultracold atoms. The lattice is formed by a single 300 nm magnetized layer of FePt, patterned using optical lithography. Our magnetic lattice consists of more than 15000 tightly confining microtraps with a density of 1250 traps/mm$^2$. Simple analytical approximations for the magnetic fields produced by the lattice are used to derive relevant trap parameters. We load ultracold atoms into at least 30 lattice sites at a distance of approximately 10 $\mu$m from the film surface. The present result is an important first step towards quantum information processing with neutral atoms in magnetic lattice potentials., Comment: 7 pages, 7 figures

The magnetic lattice of mixed-valence Mn ions in La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ is selectively diluted by partial substitution of Al or Ti for Mn. The ferromagnetic transition temperature $T_\mathrm{c}$ and the saturation magnetization $M_\mathrm{s}$ both decrease with substitution. By presenting the data in terms of selective dilution, $T_\mathrm{c}$ in the low-doping region is found to follow the relation $T_\mathrm{c}=T_\mathrm{c0}(1-n_\mathrm{p})$, where $T_\mathrm{c0}$ refers to the undiluted system and $n_\mathrm{p}$ is the dilution concentration defined as $n_\mathrm{p}=x/0.7$ or $n_\mathrm{p}=x/0.3$ for $M^\prime=$ Al or Ti, respectively. The scaling behavior of $T_\mathrm{c}(n_\mathrm{p})$ can be analyzed in the framework of the molecular-field theory and still valid when Mn is substituted by both Al and Ti. The results are discussed with respect to the contributions from ferromagnetic double exchange and other possible antiferromagnetic superexchange interactions coexisting in the material., Revtex4, 4 pages, 4 figures, 2006 Halong Conference Report

Unprecedented [Mn(II)(3)(micro(3)-F)(micro-N-N)(3)] triangular clusters with tetrazole ligands are linked by Mn(II) ions to generate a novel spin-frustrated 2D lattice exhibiting antiferromagnetic ordering.

We report the loading of a 1D permanent magnetic lattice with ultracold atoms on an atom chip. Our magnetic lattice is produced by a perpendicularly magnetised film of Gd10Tb6Fe80Co4deposited on a 10 ?m period grooved structure. A BEC is created in a Z-wire trap about 300 ?m from the surface of the chip. An atom cloud at about 5 ?K is moved adiabatically towards the lattice by an appropriate bias field. We estimate that about one hundred lattice sites are loaded with atoms about 7 ?m from the chip surface at a temperature of about 10 ?K.

We investigate experimentally and theoretically the superconducting properties of an Al thin film covering a periodic array of $\mathrm{Co}∕\mathrm{Pt}$ magnetic disks with out-of-plane magnetization for different radii of the magnetic disks and constant period of the magnetic lattice. The presence of the arrays of magnetic dots leads to a quantized displacement of the normal/superconducting phase boundary along the magnetic field axis, with each step corresponding to a flux-quantum per unit cell of the magnetic lattice. We demonstrate that this so-called field-induced superconductivity is strongly dependent not only on the chosen magnetic material and its magnetization $M$ but also on the radius $R$ of the constructed magnetic disks. Since field-induced superconductivity is directly linked to the nucleation of vortex-antivortex (V-AV) pairs, a theoretical $M\text{\ensuremath{-}}R$ equilibrium phase boundary is presented, delimiting regions of different numbers of induced V-AV pairs per magnet. A good qualitative and quantitative agreement is found between theory and experiment.

We report on a class of configurations of permanent magnets on an atom chip for producing 1D and 2D periodic arrays of magnetic microtraps with non-zero potential minima and variable barrier height for trapping and manipulating ultracold atoms and quantum degenerate gases. We present analytical expressions for the relevant physical quantities and compare them with our numerical results and with some previous numerical calculations. In one of the configurations of permanent magnets, we show how it is possible by changing the angle between the crossed periodic arrays of magnets to go from a 1D array of 2D microtraps to a 2D array of 3D microtraps and thus to continuously vary the barrier heights between the microtraps. This suggests the possibility of performing a type of `mechanical' BEC to Mott insulator quantum phase transition in a magnetic lattice. We also discuss a configuration of magnets which could realize a two-qubit quantum gate in a magnetic lattice., 18 pages

In several past studies, model independent analysis, in conjunction with a virtual accelerator model, has been successful in improving PEP-II linear geometric optics. In many cases, optics improvement yielded an increase in machine luminosity. In this study, an updated characterization of linear optics is presented. With the PEP-II beam position monitor (BPM) system, four independent beam centroid orbits were extracted and used to determine phase advances and linear Green's functions among BPM locations. A magnetic lattice model was then constructed with a singular value decomposition-enhanced least-square fitting of phase advances and Green's functions, which are functions of quadrupole strengths, sextupole feed-downs, as well as BPM errors, to the corresponding measured quantities. The fitting process yielded a machine model that matched the measured linear optics of the real machine and was therefore deemed the virtual accelerator. High beta beat, as well as linear coupling, was observed in both LER and HER of the virtual accelerator. Since there was higher beta beating in LER, focus was shifted to the improvement of this ring. By adjusting select quadrupoles of the virtual LER and fitting the resulting beta functions and phase advances to those of the desired lattice, the average beta beat of themore » virtual machine was effectively reduced. The new magnet configuration was dialed into LER on August 10, 2006, and beta beat was reduced by a factor of three. After fine tuning HER to match the improved LER for optimal collision, a record peak luminosity of 12.069 x 10{sup 33} cm{sup -2} s{sup -1} was attained on August 16, 2006.« less

The magnetic lattice of mixed-valence Mn ions in ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ is selectively diluted by the partial substitution of Mn by Al or Ti. The ferromagnetic-paramagnetic transition temperature ${T}_{\mathrm{c}}$ and the saturation moment ${M}_{\mathrm{s}}$ decreases with substitution in both series. The volume fraction of the nonferromagnetic phases evolves nonlinearly with the substitution concentration and faster than theoretically expected. By presenting the data in terms of selective dilution, the reduction of ${T}_{\mathrm{c}}$ is found to be scaled by the relative ionic concentration and is consistent with a prediction derived from molecular-field theory.

The analogy between geometric optics and Hamiltonian mechanics is used to propose an experiment that simulates the beam propagation in a focusing magnetic lattice of a particle accelerator. A laser beam is reflected several times by a parabolic mirror and the resulting pattern is registered by a photo camera. This experiment allows to illustrate some aspects of nonlinear beam transport in presence of nonlinearities and stochastic perturbations. The experimental results are discussed and compared with computer simulations.

Magnetic trapping potentials for atoms on atom chips are determined by the current flow in the chip wires. By modifying the shape of the conductor we can realize specialized current flow patterns and therefore micro-design the trapping potentials. We have demonstrated this by nano-machining an atom chip using the focused ion beam technique. We built a trap, a barrier and using a BEC as a probe we showed that by polishing the conductor edge the potential roughness on the selected wire can be reduced. Furthermore we give different other designs and discuss the creation of a 1D magnetic lattice on an atom chip., Comment: 6 pages, 8 figures