Experimental studies of magnetism of trimer chains

Trimer chains with J1-J2-J2 and J1-J1-J2 interactions exist in Cu3(P2O6OH)2 and ANi3P4O14 (A=Ca, Sr, Ba, Pb), respectively, where J1 and J2 denote exchange interaction parameters in the first-shortest and second-shortest bonds, respectively. A 1/3 magnetization plateau was observed in the spin-12 compound Cu3(P2O6OH)2. Experimental results of magnetic susceptibility and magnetization agree well with quantum Monte Carlo results for the trimer chain with the antiferromagnetic (AF) interactions whose values are J1=95K and J2=28K. Cu3(P2O6OH)2 is the first model compound of trimer chains with only AF interactions showing a magnetization plateau. In the spin-1 compound ANi3P4O14, a magnetic phase transition occurs and a small spontaneous magnetization appears at low temperatures. Experimental results are explainable qualitatively by ferrimagnetic long-range order in chains with AF J1 and ferromagnetic J2 interactions and by imperfect cancellation of net magnetic moments of the chains. This is the first observation of ferrimagnetic long-range order whose origin is the periodicity of the exchange interactions in the chains