R. Khasanov, V. Sazgari, T. J. Hicken, Igor Plokhikh, Marisa Medarde, Ekaterina Pomjakushina, L. Keller, Vladimir Pomjakushin, M. Bartkowiak, Szymon Królak, Michał J. Winiarski, Alexander Steppke, Jonas A. Krieger, H. Luetkens, Tomasz Klimczuk, Christof W. Schneider, Dariusz Jakub Gawryluk, Zurab Guguchia
Understanding the interplay between magnetism and superconductivity in nickelate systems is a key objective in condensed matter physics. Gaining microscopic insights into magnetism—particularly as it emerges near superconductivity—requires a synergistic approach that combines complementary experimental techniques with controlled tuning of external parameters. In this paper, we present a systematic investigation of the three-layer Ruddlesden-Popper (RP) nickelate La 4 Ni 3 O 10 using muon-spin rotation/relaxation ( μ SR ) and resistivity measurements. At ambient pressure, two incommensurate spin-density-wave (SDW) transitions are identified at T SDW ≃ 132 K and T * ≃ 80 – 90 K . Comparison of the observed internal magnetic fields with dipole-field calculations reveals a magnetic structure consistent with antiferromagnetically coupled SDW order on the outer two Ni-O layers, with smaller moments on the inner Ni-O layer. Above T * , the moments lie primarily in the a b plane, but below this temperature they undergo a subtle distortion and develop a c -axis component. The internal fields at the muon stopping sites appear abruptly at T SDW , suggesting a first-order-like nature of the SDW transition, which is closely linked to the charge-density wave (CDW) order occurring at the same temperature ( T SDW = T CDW ). Under applied pressure, all transition temperatures—including T SDW , T * , and T CDW —are suppressed at a nearly uniform rate of ≃ − 13 K/GPa. This behavior contrasts with that of the two-layer RP nickelate La 3 Ni 2 O 7 , where pressure enhances the separation between the SDW and CDW transitions. The oxygen-isotope substitution ( O 16 → O 18 ) reveals that the CDW transition temperature shifts to higher values in the O 18 -substituted samples. The isotope effect on T SDW and T * differs significantly. Specifically, when the CDW and SDW orders are intertwined, a notable isotope effect is observed on T SDW , leading to equal transition temperatures and nearly identical isotope shifts for both T CDW and T SDW . In contrast, at T * , where the SDW transition occurs independently of th