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Inelastic neutron scattering was used to study the effect of 5 and 40 mol% cholesterol on the lateral nanoscale dynamics of phospholipid membranes. By measuring the excitation spectrum at several lateral q (||) values (up to q (||) = 3 Å(-1)), complete dispersion curves were determined of gel, fluid and liquid-ordered phase bilayers. The inclusion of cholesterol had a distinct effect on the collective dynamics of the bilayer's hydrocarbon chains; specifically, we observed a pronounced stiffening of the membranes on the nanometer length scale in both gel and fluid bilayers, even though they were experiencing a higher degree of molecular disorder. Also, for the first time we determined the nanoscale dynamics in the high-cholesterol liquid-ordered phase of bilayers containing cholesterol. Namely, this phase appears to be "softer" than fluid bilayers, but better ordered than bilayers in the gel phase.

High-temperature (high-Tc) superconductivity in the copper oxides arises from electron or hole doping of their antiferromagnetic (AF) insulating parent compounds. The evolution of the AF phase with doping and its spatial coexistence with superconductivity are governed by the nature of charge and spin correlations and provide clues to the mechanism of high-Tc superconductivity. Here we use a combined neutron scattering and scanning tunneling spectroscopy (STS) to study the Tc evolution of electron-doped superconducting Pr0.88LaCe0.12CuO4-delta obtained through the oxygen annealing process. We find that spin excitations detected by neutron scattering have two distinct modes that evolve with Tc in a remarkably similar fashion to the electron tunneling modes in STS. These results demonstrate that antiferromagnetism and superconductivity compete locally and coexist spatially on nanometer length scales, and the dominant electron-boson coupling at low energies originates from the electron-spin excitations., Comment: 30 pages, 12 figures, supplementary information included

We review inelastic neutron scattering experiments performed on single crystal of the heavy fermion superconductor PrOs 4 Sb 12 . The low lying excitation spectrum consist of a singlet–triplet crystal field transition modulated by quadrupolar intersite interactions. The evolution of this so-called quadrupolar exciton on crossing the superconducting transition was studied both as a function of temperature and magnetic field. Our measurements point out the coupling between the quadrupolar fluctuations and the superconductivity.

As interest in low-temperature physics increases, whether for the study of frustrated magnets or for quantum effects, neutron spin-echo will become increasingly important, because of the high-energy resolution achievable. The behaviour of quasielastic scattering for low temperatures relative to the energy scale of interest is investigated. In addition, we note that momentum-transfer selective magnetic scattering may be susceptible to parasitic echoes in certain experimental configurations.

By comprehensive neutron diffraction measurements we have studied the magnetic structure of aegirine $({\mathrm{NaFeSi}}_{2}{\mathrm{O}}_{6})$ in and above its multiferroic phase. Natural aegirine exhibits two magnetic transitions into incommensurate magnetic order with a propagation vector of ${\stackrel{P\vec}{k}}_{\mathrm{inc}}=(0,\ensuremath{\sim}0.78,0)$. Between 9 and 6 K, we find a transverse spin-density wave with moments pointing near the $c$ direction. Below 6 K, magnetic order becomes helical and spins rotate in the $ac$ plane. The same irreducible representation is involved in the two successive transitions. In addition, the ferroelectric polarization $\stackrel{P\vec}{P}$ appearing along the $b$ direction cannot be described by the most common multiferroic mechanism but follows $\stackrel{P\vec}{P}\ensuremath{\propto}{\stackrel{P\vec}{S}}_{i}\ifmmode\times\else\texttimes\fi{}{\stackrel{P\vec}{S}}_{j}$. Synthetic ${\mathrm{NaFeSi}}_{2}{\mathrm{O}}_{6}$ does not exhibit the pure incommensurate helical order but shows coexistence of this order with a commensurate magnetic structure. By applying moderate pressure to natural aegirine, we find that the incommensurate magnetic ordering partially transforms to the commensurate one, underlining the nearly degenerate character of the two types of order in ${\mathrm{NaFeSi}}_{2}{\mathrm{O}}_{6}$.

This topical review presents results from neutron inelastic scattering experiments on single crystals of UPd2Al3. The focus is on the experimental situation, while the sequel paper advances theoretical perspectives. We present a detailed and complete characterization of the wavevector- and energy-dependent magnetization dynamics in UPd2Al3 as measured by neutron inelastic scattering primarily in the form of extensive surveys in energy–momentum space under a wide range of experimental conditions, and put our observations in context with data that has been published previously by two independent groups. In this way we emphasize the robustness of the results, which indicate the intricate nature of the dynamic magnetic susceptibility of this material. This study yields unique insight into the low-temperature ground state, which exhibits a microscopic coexistence of antiferromagnetism and superconductivity, making UPd2Al3 one of the most accessible heavy-fermion superconductors that can be fully characterized by neutron spectroscopy.

An asymmetric shift in the position of the magnetic Bragg peak with respect to the fiducial lattice has been observed by resonant x-ray scattering in a diverse series of antiferromagnetic compounds. A possible explanation is given in terms of a generalized Berry phase correction.

Neutronen sind elektrisch neutral und haben ein magnetisches Moment. Deshalb eignen sie sich besonders zur Aufklarung der Struktur und Bewegung der Atome und der magnetischen Momente im Festkorper. Forscher am Institut Laue-Langevin konnten mit der Neutronen-Flugzeitspektroskopie die Rolle der Gitterschwingungen im Supraleiter Magnesium-Diborid aufklaren. Diffraktion mit polarisierten Neutronen kann die raumliche Verteilung der Magnetisierungsdichte zum Beispiel in einem Nanomagneten sichtbar machen. Neutronen-Dreiachsspektroskopie und -Kleinwinkelstreuung offnen den Zugang zum Wechselspiel zwischen Magnetismus und Supraleitung in Hochtemperatur- und Schwere-Fermionen-Supraleitern.

Neutron spectroscopy investigations into the magnetic dynamical response of the heavy Fermion superconductor UPd2Al3 support the notion of an interplay between magnetism and superconductivity in strongly correlated f-electron systems. After introducing the scientific framework we review the neutron experiments performed over the last few years. These studies highlight the experimental challenges and allow us to identify the instrumental requirements for such investigations. We conclude our paper on the recent technical achievements as well as future developments for three-axis spectroscopy (TAS) at the ILL.

We here present inelastic neutron scattering results on the strongly correlated cubic superconductor UBe13 (T-c = 0.85 K) obtained on a large single crystal by high-resolution cold neutron three-axis spectroscopy. We observed spin dynamics at a unique momentum space position building up below T similar to 50 K and changing significantly on entering the superconducting state. The observed short-range longitudinal character of the correlations can be understood as a result of competing magnetic interactions. The energy dependence in the normal state reflects the energy scales determined from specific heat, whereas the low-temperature data suggest the opening of a superconducting gap. Our findings are consistent with a superconducting order parameter exhibiting s +/- or d-wave symmetry and placing pure UBe13 in the strong coupling regime. (Less)

The time dependence of switching multiferroic domains in ${\mathrm{MnWO}}_{4}$ has been studied by time-resolved polarized neutron diffraction. Inverting an external electric field inverts the chiral magnetic component within rise times ranging between a few and some tens of milliseconds in perfect agreement with macroscopic techniques. There is no evidence for any faster process in the inversion of the chiral magnetic structure. The time dependence is well described by a temperature-dependent rise time suggesting a well-defined process of domain reversion. As expected, the rise times decrease when heating towards the upper boundary of the ferroelectric phase. However, switching also becomes faster upon cooling towards the lower boundary, which is associated with a first-order phase transition.

High-resolution neutron inelastic scattering has been used to probe the magnetic response in the heavy-fermion superconductor ${\mathrm{UNi}}_{2}{\mathrm{Al}}_{3}.$ Quasielastic scattering has been observed both below and above ${T}_{c}$ in the vicinity of the incommensurate magnetic ordering vector ${\mathbf{Q}}_{0}=(0.39,0,0.5).$ Features in the response are similar to those reported recently for the isostructural compound ${\mathrm{UPd}}_{2}{\mathrm{Al}}_{3}.$ However, in contrast to the situation in ${\mathrm{UPd}}_{2}{\mathrm{Al}}_{3},$ no spectral gap has been observed in the dynamical susceptibility of ${\mathrm{UNi}}_{2}{\mathrm{Al}}_{3},$ even at the lowest temperature of 0.2 K.

Neutron scattering results on single crystals shed light on the static and dynamic properties of the superconductor (T sc = 18 K) PuCoGa 5 and its isostructural but antiferromagnetic (T N = 47 K) homologue NpCoGa 5 . By polarized neutron diffraction the magnetization density in the paramagnetic state of both compounds has been inferred. The microscopic magnetization of NpCoGa 5 is consistent with the orbital and spin components of a localized Np 3+ magnetic moment. In the case of PuCoGa 5 the microscopic magnetization is small, temperature-independent and cannot be described as a localized Pu 3+ magnetic moment. For NpCoGa 5 a dynamic magnetic signal has been observed by three-axis spectroscopy in the antiferromagnetically ordered state. The magnetic signal is strongest at the antiferromagnetic zone center and an energy transfer of about 5 meV. Magnetic fluctuations persist at this position in the paramagnetic state. The dynamic response is similar to the dynamic response observed in other actinide intermetallic compounds. This supports the possibility that magnetic fluctuations could also be present in the paramagnetic superconductor PuCoGa 5 .

The primary spectrometer of the ILL's thermal-beam three-axis spectrometer IN8 has recently been rebuilt to increase the instrument flexibility as well as the monochromatic flux at the sample position. Further improvement of the instrument is now envisaged and consists in the installation of a multianalyser detector system to multiplex the secondary spectrometer. This will enable one to obtain images of selected regions in (Q,ω) space. The design of such a multiplexed secondary spectrometer is based on analytical results reflecting the geometrical considerations and computer simulations performed using the neutron ray-tracing package McStas.

Resonant magnetic X-ray scattering was employed to investigate the magnetic state of epitaxial a* oriented thin films of the heavy fermion superconductor UNi2Al3. The observed incommensurate propagation vector as well as the Ne\(\acute{\rm e}\)l temperature correspond to those of bulk samples. The 1200 \({\rm \AA}\) film shows magnetic order with a correlation length >800 A parallel to the growth axis. Out of the three possible magnetic domains the one with the moment direction perpendicular to the film surface is not realized.

We report the results of inelastic neutron scattering experiments performed with triple-axis spectrometers to investigate the low-temperature collective dynamics in the ordered phase of uranium dioxide. The results are in very good agreement with the predictions of mean-field random phase approximation calculations, emphasizing the importance of multipolar superexchange interactions. By comparing neutron scattering intensities in different polarization channels and at equivalent points in different Brillouin zones, we show the mixed magnetovibrational-quadrupolar character of the observed excitations. The high-energy resolution afforded by the cold triple-axis spectrometer allowed us to study in detail the magnon-phonon interaction giving rise to avoided crossings along the $[00\ensuremath{\xi}]$ reciprocal space direction.

The control of ferroelastic, ferroelectric, and ferromagnetic domains through the corresponding fields has led to numerous applications taken for granted nowadays. Ferrotoroidal order on the other hand has been less explored due to its more complex character and due to the peculiar field needed to control it. LiFeSi${}_{2}$O${}_{6}$ exhibits a ferrotoroidal order that is particularly simple to analyze. By performing neutron-diffraction experiments with spherical polarization analysis we show that crossed electric and magnetic fields allow us to control ferrotoroidal moments.

The spin waves in the multi-k antiferromagnet, USb, soften and become quasielastic well below the AFM ordering temperature, T_N. This occurs without a magnetic or structural transition. It has been suggested that this change is in fact due to de-phasing of the different multi-k components: a switch from 3-k to 1-k behaviour. In this work, we use inelastic neutron scattering with tri-directional polarisation analysis to probe the quasielastic magnetic excitations and reveal that the 3-k structure does not de-phase. More surprisingly, the paramagnetic correlations also maintain the same clear phase correlations well above T_N (up to at least 1.4T_N). This precursor regime has not been observed before in a multi-k system.

Polarized inelastic neutron scattering under a magnetic field is used to get a microscopic insight into the spin resonance of the heavy fermion superconductor CeCoIn(5). The resonance line shape is found to depend on the neutron polarization: Some of the spectral weight is common to the two polarization channels while the remaining part is distributed equally between them. This is evidence for the spin resonance being a degenerate mode with three fluctuation channels: A Zeeman split contribution and an additional longitudinal mode.

Polarized and unpolarized neutron scattering experiments on the frustrated ferromagnetic spin-1/2 chain LiCuVO4 show that the phase transition at HQ of 8 Tesla is driven by quadrupolar fluctuations and that dipolar correlations are short-range with moments parallel to the applied magnetic field in the high-field phase. Heat-capacity measurements evidence a phase transition into this high-field phase, with an anomaly clearly different from that at low magnetic fields. Our experimental data are consistent with a picture where the ground state above HQ has a next-nearest neighbour bond-nematic order along the chains with a fluid-like coherence between weakly coupled chains., Comment: 5 pages, 4 figures. To appear in Phys. Rev. Lett

This paper provides an analysis of neutron inelastic scattering experiments on single crystals of UPd(2)Al(3). The emphasis is on establishing robust general inferences on the joint antiferromagnetic-superconducting state that characterizes UPd(2)Al(3) at low temperatures. A distinction is drawn between these conclusions and various theoretical perspectives of a more model-sensitive nature that have been raised in the literature.

The anisotropy of magnetic fluctuations propagating along the [1 1 0] direction in the ordered phase of uranium antimonide has been studied using polarized inelastic neutron scattering. The observed polarization behavior of the spin waves is a natural consequence of the longitudinal 3-k magnetic structure; together with recent results on the 3-k-transverse uranium dioxide, these findings establish this technique as an important tool to study complex magnetic arrangements. Selected details of the magnon excitation spectra of USb have also been reinvestigated, indicating the need to revise the currently accepted theoretical picture for this material.

Following a previous (multi-part) volume on Neutron Scattering within the same series (volume 23) published in the mid 1980s, several well-respected colleagues in our beloved field have contributed...

The heavy fermion superconductor UPd2Al3 exhibits the unusual combination of an antiferromagnetic phase transition, at T N =14.3 K , followed by a superconducting phase transition below 2 K without destruction of the ordered magnetic moment. In the superconducting phase the low-energy magnetic inelastic response is qualitatively of a different form from that above Tc. We review this low-energy response.

We report on inelastic neutron-scattering measurements that find itinerantlike incommensurate magnetic excitations in the normal state of superconducting ${\text{FeTe}}_{0.6}{\text{Se}}_{0.4}$ $({T}_{c}=14\text{ }\text{K})$ at wave vector ${\mathbf{Q}}_{inc}=(1/2\ifmmode\pm\else\textpm\fi{}ϵ,1/2\ensuremath{\mp}ϵ)$ with $ϵ=0.09(1)$. In the superconducting state only the lower energy part of the spectrum shows significant changes by the formation of a gap and a magnetic resonance that follows the dispersion of the normal-state excitations. We use a four band model to describe the Fermi-surface topology of this iron-based superconductors with the extended $s(\ifmmode\pm\else\textpm\fi{})$ symmetry and find that it qualitatively captures the salient features of these data.

We have studied the two-dimensional S=1/2 square-lattice antiferromagnet Cu(pz)_{2}(ClO4)_{2} (where pz denotes pyrazine), using neutron inelastic scattering and series expansion calculations. We show that the presence of antiferromagnetic next-nearest-neighbor interactions enhances quantum fluctuations associated with resonating valence bonds. Intermediate magnetic fields lead to a selective tuning of resonating valence bonds and a spectacular inversion of the zone-boundary dispersion, providing novel insight into 2D antiferromagnetism in the quantum limit.

Inelastic neutron-scattering experiments on the high-temperature superconductor La1.855Sr0.145CuO4 reveal a magnetic excitation gap Delta that decreases continuously upon application of a magnetic field perpendicular to the CuO2 planes. The gap vanishes at the critical field required to induce long-range incommensurate antiferromagnetic order, providing compelling evidence for a field-induced soft-mode driven quantum phase transition.

We have performed polarized inelastic neutron scattering experiments in the ordered phase of neptunium dioxide. The observation of magnetic scattering between 11 and 18 meV can be attributed to a transition between two states with the same expectation value of the electric quadrupole but opposite values of the magnetic triakontadipole. In contrast to resonant x-ray scattering, which detects the secondary order parameter (electric quadrupoles) associated with the 25 K phase transition, the results reported here are a manifestation of the primary (magnetic) order parameter. The experimental observations are discussed in relation to the current theoretical understanding of the low-energy magnetic dynamics of ${\text{NpO}}_{2}$.

We report on the structural instability of ${\text{Ni}}_{2}\text{MnAl}$ from calorimetry measurements and inelastic neutron scattering. The acoustic and optical phonon dispersions along the high-symmetry $[\ensuremath{\xi}00]$, $[\ensuremath{\xi}\ensuremath{\xi}0]$, and $[\ensuremath{\xi}\ensuremath{\xi}\ensuremath{\xi}]$ directions have been interpolated from the normal modes of vibration using the Born--von K\'arm\'an model. The tendency of ${\text{Ni}}_{2}\text{MnAl}$ to undergo a martensitic transformation shows up in the anomalous phonon softening of the particular ${\text{TA}}_{2}[\ensuremath{\xi}\ensuremath{\xi}0]$ phonons in the $\ensuremath{\xi}$ range 0.1--0.25 rlu of two different crystals. The phonon frequencies of this branch scale inversely with the valence electron concentration in good agreement with ab initio calculations. Contrary to the prediction of first-principles calculations in the Heusler $\text{L}{2}_{1}{\text{-Ni}}_{2}\text{MnAl}$, no anomaly is seen in the optical phonons measured in $\text{B}2{\text{-Ni}}_{2}\text{MnAl}$. The anomalous ${\text{TA}}_{2}[\ensuremath{\xi}\ensuremath{\xi}0]$ phonon softening is not enhanced below room temperature when ${\text{Ni}}_{2}\text{MnAl}$ orders in the antiferromagnetic state.

By using single crystals and polarized neutrons, we have measured the orbital and spin components of the microscopic magnetization in the paramagnetic state of NpCoGa(5) and PuCoGa(5). The microscopic magnetization of NpCoGa(5) agrees with that observed in bulk susceptibility measurements and the magnetic moment has spin and orbital contributions as expected for intermediate coupling. In contrast, for PuCoGa(5), which is a superconductor with a high transition temperature, the microscopic magnetization in the paramagnetic state is small, temperature-independent, and significantly below the value found with bulk techniques at low temperatures. The orbital moment dominates the magnetization.

We report the results of inelastic neutron scattering experiments on NpCoGa$_{5}$, an isostructural analogue of the PuCoGa$_{5}$ superconductor. Two energy scales characterize the magnetic response in the antiferromagnetic phase. One is related to a non-dispersive excitation between two crystal field levels. The other at lower energies corresponds to dispersive fluctuations emanating from the magnetic zone center. The fluctuations persist in the paramagnetic phase also, although weaker in intensity. This supports the possibility that magnetic fluctuations are present in PuCoGa$_{5}$, where unconventional d-wave superconductivity is achieved in the absence of magnetic order.

The magnetic excitations in multiferroic TbMnO3 have been studied by inelastic neutron scattering in the spiral and sinusoidally ordered phases. At the incommensurate magnetic zone center of the spiral phase, we find three low-lying magnons whose character has been fully determined using neutron-polarization analysis. The excitation at the lowest energy is the sliding mode of the spiral, and two modes at 1.1 and 2.5 meV correspond to rotations of the spiral rotation plane. These latter modes are expected to couple to the electric polarization. The 2.5 meV mode is in perfect agreement with recent infrared-spectroscopy data giving strong support to its interpretation as a hybridized phonon-magnon excitation.

We report on a single crystal neutron spin-echo investigation of the low-energy dynamic response in the heavy-fermion superconductor ${\mathrm{UPd}}_{2}{\mathrm{Al}}_{3}$ in the vicinity of the antiferromagnetic wave vector ${\mathbf{Q}}_{0}=(0\text{ }0\text{ }0.5)$. Well inside the superconducting phase, antiferromagnetic quasielastic scattering, which is present in the normal state, is absent for relaxation times up to 10 ns, equivalent to an energy resolution of $\ensuremath{\sim}1\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$. This places strong constraints on possible models for this magnetic superconductor.

Orbital current order of the d-density-wave type has been postulated to explain the pseudogap in high temperature superconductors. We have performed neutron scattering experiments to search for this order and show here the results obtained on an YBa2Cu3O6.45 sample using the best neutron spectrometers available. We argue that the data are consistent with a small, largely c-axis-directed moment, found below about 200 K.

Inelastic neutron scattering (INS) experiments and random phase approximation calculations have been used to investigate the low energy spin wave excitations in PrNi2Si2. The modulated magnitude of the ordered magnetic moments of Pr3+ ions implies that the associate, longitudinally polarized magnetic excitations are more intense and dispersive than the usual transverse spin waves. Within the random phase approximation the results are in good overall agreement with the predictions made by the model determined previously from the paramagnetic excitations. The most unusual observation is the well defined amplitude mode detected close to the magnetic Bragg point existing simultaneously with the phason mode. At low energies, an extra mode is observed to hybridize with the magnetic phasons in the neighborhood of the magnetic Brillouin zone center. A magnetoelastic interaction between the magnetic excitations and the longitudinal phonons is able to explain part of the disturbances, but it is concluded that the extra mode must be of some other, unknown origin. (Less)

Polarized and unpolarized neutron diffraction has been used to search for magnetic order in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x}$ superconductors. Most of the measurements were made on a high quality crystal of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.6}.$ It is shown that this crystal has highly ordered ortho-II chain order, and a sharp superconducting transition. Inelastic scattering measurements display a very clean spin-gap and pseudogap with any intensity at 10 meV being 50 times smaller than the resonance intensity. The crystal shows a complicated magnetic order that appears to have three components. A magnetic phase is found at high temperatures that seems to stem from an impurity with a moment that is in the $a\ensuremath{-}b$ plane, but disordered on the crystal lattice. A second ordering occurs near the pseudogap temperature that has a shorter correlation length than the high temperature phase and a moment direction that is at least partly along the c axis of the crystal. Its moment direction, temperature dependence, and Bragg intensities suggest that it may stem from orbital ordering of the d-density wave type. An additional intensity increase occurs below the superconducting transition. The magnetic intensity in these phases does not change noticeably in a 7 T magnetic field aligned approximately along the c axis. Searches for magnetic order in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ show no signal while a small magnetic intensity is found in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.45}$ that is consistent with the c axis directed magnetic order. The results are contrasted with other recent neutron measurements.

Inelastic neutron scattering experiments on the charge ordered state of Yb4As3 have been performed under magnetic field up to about 6 T. The observed dependence of the magnetic response from the one-dimensional Yb3+ chains on the applied magnetic field is well understood by the quantum sine-Gordon theory for the staggered field effect due to the existence of the Dzyalosinsky–Moriya interaction.

Spherical neutron polarimetry in the antiferromagnetic state of monocrystalline ${\mathrm{UNi}}_{2}{\mathrm{Al}}_{3}$ has established that the magnetic structure in zero field is an amplitude modulated magnetization density wave with moment axis along the ${\mathbf{a}}^{*}$ direction of the basal plane in the hexagonal structure. There is no observable change in the orientation of the magnetic moments when the material becomes superconducting below 1 K.

Neutron ray-tracing simulations have been done in order to study the interplay between an elliptically shaped guide end with two double focusing monochromators - pyrolytic graphite PG002 and bent Si111. The primary aim of these calculations has been the optimisation of the neutron optics of the new cold triple-axis spectrometer ThALES, the successor of the IN14 spectrometer at the Institut Laue-Langevin, Grenoble. The obtained results are, nevertheless, general and independent of the specific geometry of ThALES. The beam characteristics in terms of flux, real space and angular distribution and energy resolution at the sample position are presented for both cases.

We have investigated how a magnetic field applied perpendicular to the CuO2 planes of the near-optimally hole-doped high-temperature superconductor La1.855Sr0.145CuO4 (Tc ≈36 K) influences the low-energy magnetic excitation spectrum. Our detailed single-crystal neutron scattering experiments reveal that the gap to magnetic excitations falls off linearly with increasing field and reaches zero at the magnetic field µ0Hs=7±1 T required to induce long-range incommensurate magnetic order. A comparison with the electron-doped cuprate Nd1.85Ce0.15CuO4 is made and the possible link between field-induced magnetic order and Fermi surface reconstruction in cuprates is discussed.