Yoshihiro Koike

Coupling between magnetic and superconducting order parameters and evidence for the spin excitation gap in the superconducting state of a heavy fermion superconductor UPd2Al3

Neutron scattering experiments have been carried out in order to study the interplay between magnetism and superconductivity in a heavy fermion superconductor, UPd 2 Al 3 . We have observed 1% suppression of the (0 0 0.5) magnetic peak intensity below the superconducting transition temperature T c . This is direct evidence for the coupling of the magnetic order parameter with the superconducting one. Furthermore, we have observed a spin excitation gap associated with superconductivity. The gap energy Δ E g increases continuously from Δ E g = 0 to 0.4 meV with decreasing temperature from T c to 0.4 K. This gap energy corresponds to 2 k B T c , which is smaller than the superconducting gap expected from the BCS theory (3.5 k B T c ). These results are indicative of the strong interplay between magnetism and superconductivity.

Interplay between magnetism and superconductivity in URu2Si2 studied by neutron scattering experiments

Neutron scattering experiments have been carried out for a heavy fermion superconductor URu 2 Si 2 . We found that the (1 0 0) magnetic Bragg peak intensity is reduced by 1–2% in magnitude below the superconducting transition temperature of 1.15 K. This is direct evidence of the interplay between magnetism and superconductivity in URu 2 Si 2 .

Long Range Antiferromagnetic Ordering Observed Below 20 mK in the Heavy Fermion Superconductor UPt3.

Ultralow-temperature neutron scattering experiments have been carried out in order to study the antiferromagnetic ordering in the heavy fermion superconductor UPt 3 . We observed the (0.5 0 1) antiferromagnetic peak below 5 K. We found a finite spin correlation length of about 300 A above 50 mK. The peak intensity increases linearly with decreasing temperature, and is suppressed below the superconducting transition temperature of about 0.56 K. The moment size of 0.04 µ B /U was estimated from the peak intensity. These behaviors are in full agreement with results of previous studies. Surprisingly, the antiferromagnetic peak exhibits considerable narrowing below 50 mK, and a resolution-limited peak is observed below 20 mK. This is direct evidence that the antiferromagnetic long-range ordering is realized in UPt 3 at ultralow temperatures.

Field-induced Ferromagnetic Correlation in the Metamagnetic Crossover in CeRu2Si2 as Studied by Neutron Scattering

Neutron inelastic scattering experiments have been performed on the paramagnetic heavy fermion compound CeRu 2 Si 2 in magnetic field along the crystal c -axis. Around the metamagnetic crossover field H m =7.7 T, the quasi-elastic excitation in the vicinity of the reciprocal lattice point (110) with an energy of 0.4 meV is significantly enhanced at T =0.4 K. The result indicates that the metamagnetic crossover in this compound is associated with a field-induced ferromagnetic correlation. The observation is consistent with the recent theoretical prediction by Satoh and Ohkawa based on quasi-particle band spectrum considerations.

Neutron Scattering Study on the Crystal Structure, Magnetic Ordering, and Crystalline Electric Field Excitations in an Uranium Metallic Compound U3Pd20Si6

Systematic neutron scattering experiments were carried out in order to reveal the crystal and magnetic structure as well as the localized character of the uranium 5 f electrons in a ternary metalli...

Specific heat of beryllium-copper alloy at very low temperature

Abstract The specific heat of beryllium-copper alloy has been measured between 0.5 mK and 20 mK. The data are well fitted by C(T) = 3.58 × 10−9T−1.64 J g−1 K−1 in the temperature range 0.5–5 mK.

Ferromagnetic nuclear spin order of scandium

Ferromagnetic nuclear spin ordering of Sc metal was observed by a magnetic susceptibility measurement following a demagnetization cooling from the initial magnetic field of about 2.5T and the initial temperature of 0.277mK. The magnetic susceptibilities measured just after demagnetized cooling from various starting conditions were plotted against the entropies of the starting conditions. The peak of the magnetic susceptibility corresponds to the half of the entropy of the nuclear ground state doublet, I = {+-} 7/2. Magnetic field effects on the magnetic susceptibility and also magnetization were observed.

Nuclear magnetism of PrIn3

The specific heat of Van Vleck paramagnet PrIn3 has been measured in the temperature range between 0.07 mK and 10 mK. The crystal structure is a cubic Cu3Au type. Praseodymium(Pr) site has a cubic symmetry but Indium(In) site has no cubic symmetry. The specific heat result shows two anomalies. One is a broad anomaly which can be well-explained by a Schottky specific heat of the nuclear quadrupole interaction of In. The obtained nuclear quadrupole coupling constant ishvq=+228 MHz and the sign is positive. The other is a sharp anomaly at 0.13mK. This anomaly indicates the magnetic ordering of Pr in the nuclear regime. This ordering temperature is the lowest among the transition temperatures of the Van Vleck paramagnets.

Nuclear spin order of Sc metal

Abstract Ferromagnetic nuclear spin ordering of Sc metal was observed by a magnetic susceptibility measurement following a demagnetization cooling from the initial magnetic field of about 2.5T and the initial temperature of 0.277mK. Spin glass-like phenomena due to 3 ppm Fe impurities was also observed at slightly higher temperature than the nuclear spin ordering temperature.

Magnetic susceptibility of Sc single crystal

The temperature dependencies of the magnetic susceptibility of Sc metal were measured between 0.1 mK and 10 mK parallel to the c-axis of single crystal in various small magnetic fields. From the magnetic field dependence of the magnetic susceptibility, the magnetic impurity effect on the magnetic property of Sc metal is discussed.