We present a critical investigation on the structural, magnetic, and magnetotransport properties of two sets of polycrystalline SrRuO 3 samples with uniquely defined ferromagnetic transition temperatures. The ac magnetic susceptibility study exhibits the remarkable memory effect, a distinct characteristic of glassy behavior, at low temperatures. The transport study suggests a crossover from Fermi-liquid to non-Fermi-liquid behavior. Most strikingly, the temperature-dependent magnetoresistance exhibits two distinct dips (one around ferromagnetic ordering temperature and the other around 50 K), resembling a double-well potential in appearance. In addition, the temperature-dependent coercive field shows a plateau around 50 K. An attempt has been made to employ neutron diffraction to understand the genesis of such unusual low-temperature magnetic features. From the neutron-diffraction study, we find the evidence for changes in the unit-cell lattice parameters around 60 K and, thus, believe that the low-temperature anomalous magnetic response is closely intertwined to lattice-parameter change.
We report the results of a comprehensive study on dc magnetization, ac susceptibility, and the magnetotransport properties of the La(1 - x)Sr(x)CoO₃(0 ≤ x ≤ 0.5) system. At higher Sr doping (x ≥ 0.18), the system exhibits Brillouin-like field cooled magnetization (M(FC)). However, for x < 0.18, the system exhibits a kink in the M(FC), a peak at the intermediate field in the thermoremnant magnetization and a non-saturating tendency in the M-H plot that all point towards the characteristic of spin glass behavior. More interestingly, dc magnetization studies for x < 0.18 do not suggest the existence of ferromagnetic correlation that can give rise to an irreversible line in the spin glass regime. The ac susceptibility study for x > 0.2 exhibits apparently no frequency dependent peak shift around the ferromagnetic transition region. However, a feeble signature of glassiness is verified by studying the frequency dependent shoulder position in χ('')(T) and the memory effect below the Curie temperature. But, for x < 0.18, the ac susceptibility study exhibits a considerable frequency dependent peak shift, time dependent memory effect, and the characteristic spin relaxation time scale τ(o) approximately 10(- 13) s. The reciprocal susceptibility versus temperature plot adheres to Curie-Weiss behavior and does not provide any signature of preformed ferromagnetic clusters well above the Curie temperature. The magnetotransport study reveals a cross over from metallic to semiconducting-like behavior for x ≤ 0.18. On the semiconducting side, the system exhibits a large value of magnetoresistance (upto 75%) towards low temperature and it is strongly connected to the spin dependent part of the random potential distribution in the spin glass phase. Based on the above observations, we have reconstructed a new magnetic phase diagram and characterized each phase with associated properties.
The presence of both inversion (P ) and time-reversal (T ) symmetries in solids leads to well-known double degeneracy of electronic bands (Kramers degeneracy). When the degeneracy is lifted, spin textures can be directly observed in momentum space, as in topological insulators or in strong Rashba materials. The existence of spin textures with Kramers degeneracy, however, is very difficult to observe directly. Here, we use quantum interference measurements combined with first-principle band structure calculations to provide evidence for the existence of hidden entanglement between spin and momentum in antiperovskite-type 3D Dirac material Sr3SnO. We find robust weak antilocalization (WAL) independent of the position of EF, whereas clear signature of weak localization (WL) develops only when EF shifts away from the Dirac node by doping. The observed WAL signal at low doping is fitted using a single interference channel which implies that the different Dirac valleys are mixed by disorder. Notably, this mixing does not suppress WAL, suggesting contrasting interference physics compared to graphene. We identify scattering among axially spin-momentum locked states as a key process that leads to a spin orbital entanglement, giving rise to robust WAL. Our work sheds light on the subtle role of spin and pseudospin when both could contribute to the same quantum effect. arXiv:1806.08712v1 [cond-mat.mes-hall]
A series of anti-perovskites including Sr3PbO are recently predicted to be a three-dimensional Dirac material with a small mass gap, which may be a topological crystalline insulator. Here, we report the epitaxial growth of Sr3PbO thin films on LaAlO3 using molecular beam epitaxy. X-ray diffraction indicates (001) growth of Sr3PbO, where [110] of Sr3PbO matches [100] of LaAlO3. Measurements of the Sr3PbO films with parylene/Al capping layers reveal a metallic conduction with p-type carrier density of ∼1020 cm−3. The successful growth of high quality Sr3PbO film is an important step for the exploration of its unique topological properties.
We investigate by resonant inelastic x-ray scattering the magnetic excitations in thin films of tetragonal CuO. We identify a spin wave excitation, dispersing on two cupratelike antiferromagnetic sublattices. Its energy at the boundary of the Brillouin zone (220 meV), is significantly lower than typical values (E ∼ 300 meV) found in two-dimensional cuprates. A spin wave expansion starting from an extended Hubbard model suggests two possible scenarios for this energy lowering. DOI: 10.1103/PhysRevB.92.140404 PACS number(s): 74.72.Cj, 74.25.Jb, 75.30.Ds, 78.70.Ck Magnetism in the undoped, insulating quasi-twodimensional (2D) cuprates is determined by the 180• Cu-O-Cu bonds of their corner-sharing copper oxide layers [ Fig. 1(a) [3]. Phenomenologically, these systems can be described by extended spin-1/2 Heisenberg models with antiferromagnetic coupling on a square lattice [4,5], in agreement with secondorder superexchange theory. However, to make contact with other spectroscopies one needs to adopt a more microscopic description in terms of an extended Hubbard model. To be quantitative, it is necessary to go beyond second-order perturbation theory and to consider the effective spin model generated by the one-band Hubbard model up to fourth order in hopping. Such a procedure renormalizes the two-spin interactions and also leads to four-spin interactions. This approach yields more realistic values for the on-site Coulomb repulsion U , is consistent with higher-energy resonant inelastic x-ray scattering (RIXS) and angle-resolved photoemission spectroscopy (ARPES) data, and provides good fits to the experimentally observed spin excitation spectra [6,7].A recent exciting development was the discovery of a new tetragonal form of the simple binary oxide CuO, with an alternative structure to that of the cuprates. Tetragonal CuO (T-CuO) can be grown epitaxially on a SrTiO 3 (001) substrate up to a thickness of several unit cells [8][9][10]. In this material CuO 6 octahedra give rise to infinite CuO layers, consisting of edge-sharing CuO 4 plaquettes, stacked along the c axis. At variance with the CuO 2 cuprate layers, oxygen ions do not bridge nearest-neighbor (NN) but next-NN copper ions. Electronically, the edge-sharing structure is well described by two interpenetrating corner-sharing sublattices [ Fig. 1(b) • Cu-O-Cu bonds, the coupling could be either ferromagnetic or antiferromagnetic but, in any case, it introduces frustration. In the classical limit, the system would still develop independent AFM Heisenberg order on each sublattice. However, if quantum fluctuations are taken into account, J d is expected to lock the relative orientation of the two sublattices and to break the fourfold rotational C 4 symmetry, leading to an additional Ising order parameter [12][13][14].To examine these speculations, we have studied the magnetic excitation spectrum of T-CuO. Since inelastic neutron scattering is inadequate due to the limited film thickness, we employ RIXS at the Cu L 3 (Cu 2p 3/2 → 3d) edge [15]. We find a magnon...
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