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We report precision c-axis magnetic measurements on a high-quality single crystal of the heavy fermion metamagnet UCoAl. The metamagnetic transition at H M changes from 1st order at low temperature to a crossover at high temperature. H M is nearly linearly increasing with increasing temperature up to a critical temperature T 0 . The critical temperature T 0 is determined from both the field and the temperature dependences of magnetization to be ∼ 11 K. The field dependence of the Sommerfeld coefficient γ is estimated from M(T) by using a Maxwell relation. γ(H) shows a step-like decrease at H M . This behavior is consistent with the previous reports of specific heat and resistivity measurements at low temperatures. © 2013 The Korean Physical Society.

We have performed NMR measurements under pressure in UCoAl with a quantum critical endpoint of the metamagnetic transition from the paramagnetic phase to the ferromagnetic (FM) phase. 59 Co-NMR sensitively detects the evolution of the internal field caused by applying the external field. The metamagnetic field H m increases with increasing pressure consistently with other experimental methods, accompanied by the suppression of the magnetization in the field-induced FM phase and the magnetization jump at H m . The loss of the NMR signal on approaching the QCEP indicates the development of the spin fluctuations. © 2013 The Korean Physical Society.

We have studied the high-pressure magnetic property in UGe 2 where ferromagnetic superconductivity appears under high pressure. In this study, we focus on the magnetic property at pressures above the ferromagnetic critical pressure P c =1.6 GPa. The temperature and magnetic field dependences of the dc-magnetization have been measured under high pressures up to 5.1 GPa by using a ceramic anvil high pressure cell. At pressures above P c , the magnetic susceptibility x shows a broad maximum around T χmax and the magnetization at 2.0 K shows an abrupt increase (metamagnetic transition) at H c . With increasing pressure, the peak structure in x becomes broader, and the peak position T χmax moves to the higher temperature region. The metamagnetic field H c increases rapidly with increasing pressure. At pressures above 4.1 GPa, x shows a simple temperature dependence, and the magnetization increases linearly with increasing field. These phenomena in UGe 2 resemble to those in the intermetallic compounds of 3d transition metals such as Co(S 1-x Se x ) and YCo 2 . We discuss the experimental results by using the phenomenological spin-fluctuation theory. © 2013 The Korean Physical Society.