Molecular self-diffusion in internal magnetic fields of porous medium investigated by NMR MGSE method

[Display omitted] •Theory of gradient spin echo methods in a very inhogeneous magnetic field was derived.•It explains CPMG measurement of water diffusion in impurity doped ceramics. Inhomogeneous magnetic fields generated in porous media due to differences in magnetic susceptibility at solid/liquid interfaces and due to intrinsic or artificially doped magnetic impurities can be used to gain insight into the molecular dynamics of fluid in the structure of a porous medium using the concept of NMR modulated gradient spin echo method. We extended the theory of this method to the case of an inhomogeneous magnetic field that cannot be approximated by an uniform gradient, in order to explain the CPMG measurements of self-diffusion in water soaked ceramics, which are doped with magnetic impurities of different contents. The new interpretation provides the spin relaxation times, the average pore size and their distribution, as well as the strength of the internal magnetic gradient fields in the doped ceramics.