Magnetic ordering of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">Nd</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>in single-crystal<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">NdBa</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><

We performed scanning tunneling spectroscopic experiments on hole-doped NdBa2Cu3O 7−δ . The dI/dV curves obtained at 4.2 K are asymmetric with clear peak-dip and hump structures. Energy derivatives of these curves show peaks at energies beyond the dip features. Highly precise full potential bandstructure calculations confirm a featureless electronic density of states in that energy region. Our results indicate that tunneling electrons couple to a collective mode in the CuO2 plane.PACS numbers: 74.20.Mn, 74.25.Jb, 74.50+r, 74.72.Bk The identification of the microscopic mechanism for pair formation in the unconventional superconductors is still a challenge. In conventional superconductors, apart from the isotope effect, tunneling experiments provided the most direct evidence of electron-phonon interaction mediating the Cooper-pair formation [1,2]. In case of high-T c superconductors (HTSC), inelastic neutron scattering (INS) experiments and high resolution angle-resolved photo emission (ARPES) experiments were useful to find collective modes in the range of 30-70 meV [3,4,5,6,7,8,9]. Collective spin excitations have been suggested as the bosonic mode which interacts with electrons to produce a resonance peak at a wavevector (π, π) in INS spectra and a kink along the (π,0) direction of the Brillouin zone in ARPES spectra [3,4,5,6,10]. On the other hand, several ARPES results also show evidence of phonons as the collective modes [7,8,9]. Thus the assignment of the boson-mediating Cooper pair formation in HTSC is far from being settled.Due to the microscopic electronic inhomogeneity in these superconductors [11], tunneling experiments using scanning tunneling microscopy (STM) are expected to play an important role in resolving such issues being related to pairing. While tunneling, electrons can excite a collective mode of a certain energy if the energy of the electrons is equal to that of the collective mode. Due to the inelastic interaction of the electrons with the mode, a new scattering channel is induced which results in a step-like feature in the dI/dV curves [12]. Ideally, these step-like features can be observed more easily in the form of a delta function in the energy derivative of the dI/dV curves. In experiments, the peak heights and widths are dependent on the energy resolution, temperature and the modulation voltage [12]. For the superconducting state of d-wave superconductors, Balatsky et al. predicted that features due to inelastic scattering of tunneling electrons would be observed in the d 2 I/dV 2 curves as satellite peaks at ∆ + Ω in addition to a very weak peak at Ω, where ∆ is the energy gap and Ω is * Electronic address: Pintu.Das@cpfs.mpg.de

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“…They have isostructural unit cells. The ionic size of Nd 3+ ions, which are paramagnetic at 4.2 K [18], is bigger than that of Y 3+ .…”

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confidence: 89%

“…The details of the growth process are according to those mentioned in Ref. [18]. After the growth, the crystal was properly oxidized to achieve a T c onset of 93.5 K. The transition width of ∆T c ∼ 3.5 K was determined from ac-susceptibility measurements.…”

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confidence: 99%

Excitation of a bosonic mode by electron tunneling into a cuprate superconductorNdBa2Cu3O7−δ

et al. 2008

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“…In a recent work by Rotter and Boothroyd, 69 it has been shown that accounting for the anisotropic form-factor effects in NdBa 2 Cu 3 O 6+x , considering the 4f crystal field of the Nd ion, allowed for the correction of the previously accepted magnetic structure in that compound: A slight tilting of the Nd magnetic moments away from the c axis has been proven to be an artifact of the isotropic magnetic form-factor approximation used in the past. 70 Calculation of the magnetic form factor of Fe(II) using the McPhase program 71 revealed that the modeling of the magnetic structure can be considerably different when using the dipole approximation or the full approximation. The modeled magnetic intensity varies between the two approximations: The difference (I full − I dip )/I dip is less than 5% for low angles (2θ < 60 • ) but becomes larger for higher angles [(I full − I dip )/I dip > 20%].…”

Section: A End-member Ilmenite Fetiomentioning

confidence: 99%

Large spontaneous magnetostriction in FeTiO3and adjustable magnetic configuration in Fe(III)-doped FeTiO3

et al. 2012

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We present neutron diffraction data and magnetic susceptibility measurements of FeTiO 3 ilmenite and Fe(III)doped ilmenites (with 10 and 20 mol. % Fe 2 O 3) at temperatures of 1.9 K < T < 300 K. The magnetic moments of the Fe cations in FeTiO 3 lie predominantly along the c axis, with a weak component in the lateral layers. With increasing Fe(III) doping the component in the lateral layers grows and the magnetic moments are tilted inside the layers. The lattice dimensions decrease with decreasing temperature, but upon the onset of magnetic long-range order they grow strongly and FeTiO 3 exhibits large spontaneous magnetostriction in the per-mille range along the c axis at T = 1.9 K. In the Fe(III)-doped ilmenites the spontaneous magnetostriction is negligible, but application of an external field at low temperature causes a strong reduction in the unit cell dimensions as the magnetic layer configuration is changed. This is also seen in the macroscopic magnetic moment, which increases by two orders of magnitude if cooled with a magnetic field, whereas the field-cooled state exhibits a self-reversal upon heating.

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“…In the calculation with the dipole form factor the best fit is achieved with the Nd 3+ moment tilted 12°away from the c axis, as found in Ref. 22. However, when the anisotropic form factor is employed the best-fit model has the moments parallel to the c axis.…”

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Going beyond the dipole approximation to improve the refinement of magnetic structures by neutron diffraction

Rotter

Boothroyd

2009

Phys. Rev. B

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We have made an analysis of neutron-diffraction data for a number of rare-earth compounds to assess the use of the dipole approximation in magnetic structure refinements. We present two examples. In the case of CePd 2 Si 2 , our analysis confirms the published magnetic structure, but we find that use of the "exact" magnetic form factor of Ce 3+ gives a significantly improved description of the data. For NdBa 2 Cu 3 O 6+x , however, we find that incorrect conclusions have previously been drawn about the magnetic structure through the use of the dipole approximation. We have extended the magnetic modeling suite MCPHASE to enable a straightforward calculation of the higher-order anisotropic terms in the form factor of rare-earth-based systems.Neutron diffraction is the standard method for determining magnetic structures. Magnetic neutron diffraction arises from the interaction between the magnetic moment of the neutron and magnetic fields in the sample associated with orbital currents and intrinsic spin of unpaired electrons. The distribution of scattered neutrons is modulated by a form factor, which for elastic scattering is the Fourier transform of the magnetization. Most state-of-the-art magnetic structure refinement procedures employ the dipole approximation for the form factor, which assumes that the spatial distribution of magnetization in an atom or ion is isotropic. This approximation is strictly valid only in the limit of small scattering vectors, although for many problems it is accurate enough to enable the magnetic structure to be solved. However, with the best neutron-diffraction instrumentation it is possible to measure diffraction intensities with sufficient precision that the dipole approximation is not always satisfactory. For example, in recent studies on Ce-based compounds it has been shown that the modeling of diffraction data can be improved by including higher-order corrections to the dipole approximation. [1][2][3] The purpose of this Rapid Communication is twofold. First, we wish to demonstrate the importance of going beyond the dipole approximation in the analysis of magnetic neutron-diffraction data. The focus here is on rare-earth ions, but corrections to the dipole approximation are expected to be even larger for transition metals. 4,5 Second, we report the incorporation of the exact form factor into the MCPHASE modeling suite 6-10 so that rare-earth magnetic structure calculations similar to those presented here can be performed for other compounds.In the standard formalism 11 the elastic magnetic neutronscattering cross section ͑d / d⍀͒ mag is proportional to the square of the magnetic structure factor F M ,whereThe summation is over the ions indexed by d in the magnetic unit cell, with displacements R d from the origin. The scattering vector is denoted by Q, with Q = ͉Q͉, M d ͑Q͒ is the Fourier transform of the magnetization operator and exp͑−W d ͒ is the Debye-Waller factor. In the dipole approximation, ͗M d ͑Q͒͘ may be separated into a product of a magnetic form factor f dip ͑Q͒, whi...

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Magnetic ordering ofNd3+in single-crystalNdBa2<

Cited by 5 publications

References 39 publications

Excitation of a bosonic mode by electron tunneling into a cuprate superconductorNdBa2Cu3O7−δ

Excitation of a bosonic mode by electron tunneling into a cuprate superconductorNdBa2Cu3O7−δ

Large spontaneous magnetostriction in FeTiO3and adjustable magnetic configuration in Fe(III)-doped FeTiO3

Going beyond the dipole approximation to improve the refinement of magnetic structures by neutron diffraction

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