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We describe some antiferromagnetic systems which exhibit spin gaps. We also discuss the effect of doping one such system, namely, the spin-ladders, with holes. Some model antiferromagnetic systems with spin gap are reviewed for which exact results are available. Exact results for a doped spin-ladder model are also mentioned.

Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. ...

The study of impurities in low dimensional antiferromagnets has been a very active field in magnetism ever since the discovery of high temperature superconductivity. One of the most dramatic effects is the appearance of large Knight shifts in a long range around non-magnetic impurities in an antiferromagnetic background. The dependence of the Knight shifts on distance and temperature visualizes...

The role of various types of defects in establishing the magnetic properties of the C60-based polymers and the single-wall carbon nanotubes is investigated. Comparing the role of carbon vacancies, and that of substitutional impurity atoms X X=N, B, O, Si, P, and S in establishing a magnetic ground state it is found that the impurity X atoms promote the spin density delocalization, whereas its l...

The resistivity and magnetization of layered perovskite La222xCa112xMn2O7 have been studied systematically using bulk samples with a wide doping concentration range 0<x<0.5 and epitaxial thin film samples with x50.3. The system becomes a metallic ferromagnet for doping concentrations 0.22<x<0.5. In this doping region, results for bulk samples as well as for thin films have clearly shown that th...

Here V is electrostatic potential, u, v are Slotboom concentrations of electrons and holes, λ = 10−3 − 10−6, δ = ni (intrinsic density of electrons), C ∈ L∞(Ω) is doping profile, Q is recombination-regeneration rate, q is elementary charge, μn, μp are mobilities of electrons and holes, and Vbi, U are equilibrium and applied potentials. We consider Ω = (0, 1) × (−h, 0) in R (h is some positive n...