Strong longitudinal magnetic fluctuations near critical end point in UCoAl; A Co-NMR study

Nohara, Hiroki*; Kotegawa, Hisashi*; To, Hideki*; Matsuda, Tatsuma; Yamamoto, Etsuji  ; Haga, Yoshinori   ; Fisk, Z.; Onuki, Yoshichika; Aoki, Dai*; Flouquet, J.*

We report Co-NMR measurements in UCoAl where metamagnetism occurs owing to the enhancement of ferromagnetism by a magnetic field. The metamagnetic transition from a paramagnetic (PM) state to a ferromagnetic state is a first-order transition at low temperatures, but it changes to a crossover at high temperatures on crossing the critical end point (CEP) at 12K. The contrasting behavior between the relaxation rates and suggests that the longitudinal magnetic fluctuation of the U moments is strongly enhanced, especially near the CEP.