We report magnetic properties of the antiferromagnet YMn 2 as functions of pressure and temperature ͑T͒ obtained from the 55 Mn spin-lattice relaxation rate and the Knight shift. An energy-band narrowing due to electron correlation is indicated by the Knight shift measurement and the application of pressure is found to enhance the conduction electron bandwidth. In the pressure-induced paramagnetic state, the system undergoes a crossover from an itinerant spin fluctuation ͑SF͒ regime at low T to a local SF regime at high T. It is pointed out that this magnetic crossover of SF resembles that of high-temperature superconductors.

We report the NQR study on the pressure-induced paramagnetic state in the antiferromagnetic (AF) intermetallic compound YMn 2 with the Néel temperature T N =100 K at ambient pressure. From the T variation of the nuclear spin-lattice relaxation rate, 55 (1/T 1 ) of 55 Mn above the critical pressure of 4 kbar, the spin fluctuation feature is found to change below a temperature T sf . At higher temperature than T sf , the nuclear relaxation behavior is well described in terms of the self-consistent renomalized (SCR) spin fluctuation theory for nearly AF metals, whereas below T sf a deviation is significant and 1/T 1 T exhibits a weak T variation. It is pointed out that T sf coincides with the temperature below which a T 2 law in electrical resistivity is valid as expected for a Fermi liquid ground state. We proposed that these features are understood from the standpoint that the development of AF spin fluctuation remains in short-range associated with the singlet formation among Mn spins in each tetrahedron as suggested by the inelastic neutron experiments on Y 1−x Sc x Mn 2 .

From our NMR measurements, we compare the spin fluctuations spectrum in high-T c cuprates and the pressure-induced paramagnetic state of YMn 2. It is pointed out that the latter has a shorter magnetic correlation length and the bandwidth is smaller by one order in magnitude than the former.

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