Two-dimensional spin freezing in Y1−z Ca z Ba2Cu3−x Fe x O7

Frequency Spectra of Quantum Beats in Nuclear Forward Scattering of 57Fe: The Mössbauer Spectroscopy with Superior Energy Resolution

“…Therefore, in the datapoints of the first peak at ω > 0 (ω ≈ 0) the intensity is doubled. However, additionally, in the fully enriched α-57 Fe 2 O 3 , the zero-field peak is enhanced by 66%, equivalently to the 33%-enhancement of the corresponding term in Equations (18), (23) or (28). In these equations, the relative weight of the zero-frequency peak is 14/72.…”

“…Comparison of the Fourier spectra in Figures 6(d) and 7(d) shows that all the features, except the zero-frequency line, coincide. Note, in the experimental QBFS, obtained via fast Fourier transform, the zero-frequency peak is twice more intense compared to the relative spectral weight given by the coefficients in Equations (18), (23) or (28). This enhancement results from the absence of negative frequencies.…”

“…Here we reinvestigated the sample with the greatest pairbreaking population in the Cu(2) site. The minor population of the dopants (21%) residing in the Cu(1)-site was found previously to be composed of two distinct species having tetrahedral (4%) and pyramidal (17%) coordinations [27,28]. In Mössbauer spectra, these two environments were characterized by quadrupole splittings of 1.98 mm/s and 1.2 mm/s, with isomer shifts of 0.07 mm/s and −0.06 mm/s, respectively [27,28].…”

“…The minor population of the dopants (21%) residing in the Cu(1)-site was found previously to be composed of two distinct species having tetrahedral (4%) and pyramidal (17%) coordinations [27,28]. In Mössbauer spectra, these two environments were characterized by quadrupole splittings of 1.98 mm/s and 1.2 mm/s, with isomer shifts of 0.07 mm/s and −0.06 mm/s, respectively [27,28]. In the QBFS, the signature of minor sites appears as the small peak around 17 MHz (1.5 mm/s), however, this feature does not correspond to a site quadrupolar splitting but arises from intersite interference.…”

“…Shown in Figure 2 are the NFS data obtained from Y 0.76 Ca 0.24 Ba 2 Cu 2.91 Fe 0.09 -O 7−δ and ZnFe 2 O 4 studied previously with conventional Mössbauer spectroscopy [27][28][29]. The first compound is the high-temperature superconductor with T c of 49 K, in which 79% of the Fe atoms were driven into Cu(2)-planar sites with eQV zz /2 = 0.62 mm/s.…”