This work investigates the magnetic structure of Rb 2 CuCl 4 as a function of pressure and temperature using neutron diffraction. As in most A 2 CuCl 4 layered perovskites, there is a 2D ferromagnetic order within the layers. This behaviour is due to the Jahn-Teller (JT) antiferrodistortive structure of the CuCl 6 units. Rb 2 CuCl 4 undergoes a 3D magnetic transition at T N = 16 K, which mainly depends on the weak antiferromagnetic interlayer interaction. The pressure slightly increases T N , as ∂ T N /∂ P = 0.13 K kbar −1 . This behaviour is interpreted in terms of pressure-induced tilts and reduction of interlayer distance, both effects increasing the antiferromagnetic exchange coupling between layers. The results are compared with previous magnetic studies under chemical and hydrostatic pressure along layered perovskites series of [C n H 2n+1 NH 3 ] 2 CuCl 4 (n = 1-3) and BMnF 4 (B = Li, Na, K, Rb, Tl, Cs and NH 4 ) involving JT ions of Cu 2+ and Mn 3+ , respectively. We show that the ratio of the interlayer to intralayer coupling, and thus the nature of the magnetic order, can be tuned by chemical or hydrostatic pressure along the A 2 CuCl 4 series. The present findings stress the relevance of octahedral tilts on the magnetic behaviour of layered perovskites.

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The structural and magnetic properties of the TbPt1−xCux orthorhombic compounds are studied in two series of samples: prepared ‘as quenched’ and after an annealing treatment. An extended analysis of the influence of the annealing in the microstructure of the samples was performed by x-ray, neutron diffraction and scanning electron microscopy. This analysis allows us to understand the modifications in the magnetic properties of both series, as a consequence of the sample homogenization process. Changes from ferromagnetism to antiferromagnetism with increasing Cu concentration are found in both series despite the ionic distance invariance. x = 0.3 is the composition limit between both behaviours. This study strongly supports the importance of the conduction band state rather than ionic distances in the magnetic behaviour of these rare earth–d compounds.

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