Study of Nuclear Spin Ordering

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Among a large number of pure metals, only in Cu the nuclear spins have been cooled down below their spontaneous ordering temperature. Though great efforts have been devoted to achieve the nuclear spin order, the clear evidence of oraering has not yet been observed in other metals so far. We are interested in the nuclear spin ordering in Sc metal which is known as the highly exchange enhanced Pauli paramagnetic metals. In order to achieve the nuclear spin ordering in Sc metal, we constructed two stage demagnetiziaton cryostat. Before doing the two stage demagnetized cooling experiment, we measured a temperature dependance of the magnetic susceptibility of Sc metal above 0.25 mk by the one stage demagnetized cooling. Result can be understood by the spin glass phenomenon of iron impurity in Sc metal. Then we performed the two stage semagnetized experiment. By a first stage demagntization cooling, we cooled down the Sc metal to 0.25 mk. From this temperature and 7 T initial magnetic field, nuclear spins in Sc metal was cooled down below 50 nk by the demagnetization. The warming up behaviour of the ac magnetic susceptibility has been measured following demagnetization cooling of Sc specimen itself. Amtiferromagnetic-like maximum of the magnetic susceptibility was observed. Nuclear spins stayed in the ordered state about 45 minutes. This is the second observation of the nuclear spin ordering in metal elements. But we have not yet deter mined the ordering temperature T_N. We are going to make further experiment to clear the properties of the nuclear magnetism of Sc metal.