Effect of a magnetic field on the long-range magnetic order in insulatingNd2CuO4and nonsuperconducting and superconducting

Masato Matsuura

¹

,

Pengcheng Dai

²

,

Hye Jung Kang

³

et al.

Abstract

We have measured the effect of a c-axis-aligned magnetic field on the long-range magnetic order of insulating Nd 2 CuO 4 , as-grown nonsuperconducting and superconducting Nd 1.85 Ce 0.15 CuO 4 . On cooling from room temperature, Nd 2 CuO 4 goes through a series of antiferromagnetic ͑AF͒ phase transitions with different noncollinear spin structures. In all phases of Nd 2 CuO 4 , we find that the applied c-axis field induces a canting of the AF order but does not alter the basic zero-field noncollinear spin structures. A similar behavior is also found in as-grown nonsuperconducting Nd 1.85 Ce 0.15 CuO 4 . These results contrast dramatically with those of superconducting Nd 1.85 Ce 0.15 CuO 4 , where the c-axis-aligned magnetic field induces a static, anomalously conducting, long-range ordered AF state. We confirm that the annealing process necessary to make superconducting Nd 1.85 Ce 0.15 CuO 4 also induces epitaxial, three-dimensional long-range-ordered cubic (Nd,Ce) 2 O 3 as a small impurity phase. In addition, the annealing process makes a series of quasi-two-dimensional superlattice reflections associated with lattice distortions of Nd 1.85 Ce 0.15 CuO 4 in the CuO 2 plane. While the application of a magnetic field will induce a net moment in the impurity phase, we determine its magnitude and eliminate this as a possibility for the observed magnetic-field-induced effect in superconducting Nd 1.85 Ce 0.15 CuO 4 . This is confirmed by measurements of the ͑1/2,1/2,3͒ peak, which is not lattice matched to the impurity phase.

Superconductivity in bulk T′-(La,Sm)2CuO4 prepared via a molten alkaline hydroxide route

“…In T' superconductors, the superconducting (SC) region is adjacent to the antiferromagnetic (AF) region, and the superconductivity suddenly appears at the SC-AF boundary with maximum T c [3], suggesting competition between AF and SC orders. In the "optimally" doped Pr 1.85 Ce 0.15 CuO 4 or Nd 1.85 Ce 0.15 CuO 4 , the AF correlations exist in as-grown non-superconducting samples, but they essentially disappear in reduced superconducting samples [4,5]. This implies that more complete removal of apical oxygen would weaken the AF correlations and thereby expand the superconducting region.…”

Microscopic annealing process and its impact on superconductivity in T′-structure electron-doped copper oxides

“…To test this possibility, single crystals of PLCCO (space group I4/mmm, a = 3.98 Å, c = 12.3 Å) were grown using the traveling-solvent floating-zone technique. These included four samples prepared from the same as-grown batch: as-grown nonsuperconducting (ag-NSC), reduced superconducting (r-SC), oxygenated nonsuperconducting (o-NSC), and re-reduced superconducting (r2-SC) crystals.As shown in previous work [18][19][20][21] , annealing necessary to produce superconductivity also induces epitaxial intergrowths of the cubic R 2 O 3 impurity phase.The R 2 O 3 has a cubic structure with space group Ia3 and lattice parameter a c = 2√2a ~ c/1.1, where the "c" subscript indicates "cubic". The Miller indices of the T' and impurity phases are related as ( , , ) [ To test the reversibility of the impurity phase, we carried out x-ray powder diffraction measurements on portions of the ag-NSC, r-SC, and o-NSC single crystal samples of PLCCO that were crushed into fine powders.…”

“…), electron-doping alone is insufficient, and annealing the as-grown sample in a low oxygen environment to remove a tiny amount of oxygen is necessary to induce superconductivity 2,3 . Previous work [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] suggests that oxygen reduction may influence mobile carrier concentrations 7 , decrease disorder/impurity scattering 8,10,11,23 , or suppress the long-range AF order 16,17,22 . However, the microscopic process of oxygen reduction, its effect on the large electron-hole phase diagram asymmetry and mechanism of superconductivity 2,3 are still unknown.…”

“…5%) entirely suppress AF order and superconductivity appears over a wide range of hole concentrations (from 6% to 30%). In the case of T' structured electron-doped superconductors, doping alone by substituting the trivalent ions R 3+ in R 2 CuO 4 with tetravalent Ce 4+ is insufficient to induce superconductivity and the as-grown materials such as Nd 2-x Ce x CuO 4±δ (NCCO), Pr 2-x Ce x CuO 4±δ (PCCO), and Pr 0.88 LaCe 0.12 CuO 4 (PLCCO) are semiconducting with static long-range AF order [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] .In these materials, superconductivity (maximum T c ~25 K) is achieved only when the samples within a relatively narrow dopant range (0.1≤x≤0.18) are annealed in a reducing atmosphere . The reduction process suppresses the AF order most severely at higher Ce-doping levels above x≥0.1 (ref.…”

Neutron Scattering Studies of Antiferromagnetic Correlations in Cuprates

“…An initial study [257] on Nd 2−x Ce x CuO 4 with x = 0.14 and T c ∼ 25 K found that applying a field as large as 10 T had no effect on the intensity of an antiferromagnetic Bragg peak for temperatures down to 15 K. Shortly after that came a report [258] of large field-induced enhancements of antiferromagnetic Bragg intensities, as well as new field-induced peaks of the type ( 1 2 , 0, 0), in a crystal of Nd 2−x Ce x CuO 4 with x = 0.15 and T c = 25 K. It was soon pointed out that the new ( 1 2 , 0, 0) peaks, as well as most of the effects at antiferromagnetic reflections, could be explained by the magnetic response of the (Nd,Ce) 2 O 3 impurity phase [251,252]. There now seems to be a consensus that this is the proper explanation [259,260]; however, a modest field-induced intensity enhancement has been seen at ( 1 2 , 1 2 , 3) that is not explained by the impurity-phase model [259].…”