2022 年 32 巻 1 号 p. 33-41
This article reviews our studies of unusual magnetic orderings in Yb intermetallic compounds YbNi3Ga9 and YbAgGe using high-pressure specific-heat measurements. Upon applying pressure above 9 GPa, YbNi3Ga9 with a chiral trigonal structure undergoes a magnetic order at 1.5 K. Application of magnetic field B⊥c induces another ordered phase in the B-T phase diagrams at P > 11 GPa. The origin of this induced phase is discussed in relation to the chiral soliton lattice. YbAgGe with a quasi-kagome lattice of Yb ions undergoes two magnetic transitions at 𝑇M1=0.8 K and 𝑇M2=0.65 K at ambient pressure. For 0.5 < P < P* = 1.7 GPa, the TM remains constant at 0.85 K, while the TM increases linearly with P > P*. The magnetic entropy at TM rises for P > P*, whereas the Kondo temperature TK does not change. These findings suggest that the sudden rise of TM(P) for P > P* is not due to the lowering of TK but the release of the magnetic frustration in the quasi-kagome lattice.
