La
2CuSnO
6, even though it contains CuO
2 layers, does not exhibit superconductivity. It might result from the in-plain Cu-O bond length being too long(about 2.0 Å, compared with 1.9 Å of La
2CuO
4). So, we replaced La with smaller atoms Pr, Nd, Sm, expecting that these might contract the CuO
2 layers and lead to superconductivity. For synthesis we used high pressure(6Gpa for Pr, Nd and 8Gpa for Sm). The result Is that, contrary to our wish, the CuO
2 layers buckled even more seriously and the Cu-O bond did not get shorter. In this paper, we focused on the magnetism of Ln
2CuSnO
6(Ln=La, Pr, Nd). In the temperature range of 150 to 350K, these compounds showed almost the same characteristics which have been explained assuming spin-canted weak ferromagnetism. However, Pr
2CuSnO
6and Nd
2CuSnO
6exhibited ferromagnetic behavior at lower temperature suggesting ordering of the Pr
3+(Nd
3+)moments. Antlferromagnetic coupling between the weak ferromagnetic CuO
2 layers and the ferromagnetic LnO layers has also been suggested.
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