Multiple Magnetic Transitions in a Frustrated Heavy-Fermion Antiferromagnet YbAgGe under Magnetic Field and Pressure

概要

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The magnetization $M$ and magnetoresistance of a heavy-fermion antiferromagnet YbAgGe have been measured under pressures $P$ up to 2.7 GPa and magnetic fields $B$ up to 9.5 T. This compound crystallizing in the hexagonal ZrNiAl-type structure with a quasi-kagome lattice of Yb ions has two magnetically ordered phases, namely, phase I ($T\leq T_{\text{M2}} = 0.65$ K) and phase II ($T_{\text{M2}}\leq T\leq T_{\text{M1}} = 0.8$ K). With increasing pressure to 2.2 GPa, $M$ ($B_{\| a} = 9.5$ T) at 0.3 K increases from 1.5 $\mu_{\text{B}}$/Yb to 1.8 $\mu_{\text{B}}$/Yb, while $M$ ($B_{\| c} = 9.5$ T) hardly changes. The metamagnetic transition field in $M$ ($B_{\| a}$) decreases from 4.6 T for $P = 0$ to 3.3 T for $P = 2.2$ GPa. As the pressure exceeds $P^{*} = 1.6$ GPa, both $T_{\text{M}}$ and the initial slope of $M$ ($B_{\| a}$) steeply increase and the area of phase I for $B_{\| a}$ expands. These observations suggest that the magnetic frustration of the Yb quasi-kagome lattice is partially suppressed by the application of pressure above 1.6 GPa or magnetic field $B_{\| a}$ above 4.5 T. Detailed $B$–$T$ phase diagrams under pressures up to 2.7 GPa are discussed with respect to the magnetic frustration in YbAgGe.
Physical Society of Japanの論文
2010-06-15