The Search for the Spontaneous Ferromagnetic Transition in UCoAl under the c-axis Uniaxial Pressure Studied by Nuclear-Quadrupole-Resonance Measurement

We have performed nuclear-quadrupole-resonance (NQR) measurements under the c-axis uniaxial pressure on UCoAl in order to search for the spontaneous ferromagnetic (SFM) transition in zero magnetic field and to investigate the static and dynamic properties around the transition. For this purpose, we developed an uniaxial pressure cell for nuclear-magnetic-resonance (NMR) and NQR measurements. We observed a slight shift of paramagnetic (PM) spectra above 26 MPa, but, the nuclear spin-lattice relaxation rate 1/T1 and nuclear spin-spin relaxation rate 1/T2 were not changed up to 31.7 MPa. We conclude that a clear SFM transition was not observed up to 31.7 MPa in our NQR measurements and the slight shift of the PM spectra is due to the change of electric field gradient induced by uniaxial pressure.