A simple and efficient method for synthesizing a range of hybrid nanocomposites based on a core of silica nanospheres (160, 330, and 660 nm in diameter) covered by an outer shell of superparamagnetic nanoparticles, either iron oxide or heterodimeric FePt‐iron oxide nanocrystals, is presented. The magnetic and ultrasound characterization of the resulting nanocomposites shows that they have great potential as contrast agents for dual‐mode imaging purposes, combining magnetic resonance imaging (MRI) and ultrasonography (US).

31 P nuclear and muon spin-lattice relaxation rate measurements in SrZnVO(PO4)2, a S = 1/2 frustrated magnet on a square lattice, are presented. The temperature (T ) dependence of the inplane correlation length ξ is derived and it is shown that the overall behaviour is analogous to the one found for non-frustrated systems but with a reduced spin stiffness. The temperature dependence of ξ in SrZnVO(PO4)2 is compared to the one of other frustrated magnets on a square lattice with competing nearest neighbour (J1) and next-nearest neighbour (J2) exchange couplings and it is shown that ξ progressively decreases as the ratio J2/J1 approaches the critical value leading to the suppression of long-range magnetic order. In spite of the differences in the functional form of ξ(T ) found in different vanadates, it is pointed out that the characteristic energy scale describing spin correlations in all those compounds appears to scale as |2J2 + J1|.