Takahiko Kamigaichi

Pressure-induced magnetic transition in EuSe

Abstract The weak field a.c. susceptibility of EuSe was measured as functions of temperature from 1.5 to 15 K and of hydrostatic pressure up to 15 kbar. The Neel temperature did not change with pressure, and a new pressure-induced ferromagnetic phase appeared in the region above 4.6 K and above 4.5 kbar (triple point).

Magnetic and NMR studies of EuSe1−xSx (x ⩽ 0.3)

Abstract The magnetic phases of EuSe1−xSx(x ⩽ 0.3) were investigated by measuring 153Eu NMR and ac susceptibilities. The antiferromagnetic NNSS and ferromagnetic phases exist for 0.01 ⩽ x ≲ 0.10 and for x ≳ 0.10, respectively. The phase changes are ascribed to a sensitive dependence of J1 on the lattice constant.

NMR Study of Hyperfine Field at 153Eu in EuSe1-xTex with x ≤0.1

The 153 Eu NMR in EuSe 1- x Te x with x ≤0.1 has been observed in the temperature range between 1.7 and 4.2 K. The results of NMR, together with those of differential magnetic susceptibilities, show that the Type II antiferromagnetic (NSNS) phase or EuSe is stabilized by substituting a small amount or Te. In the NSNS phase of EuSe 1- x Te x the 153 Eu NMR frequency extrapolated to 0 K is independent of x and is 121.8 MHz, corresponding to a field of 262.6 kOe. The 153 Eu hyperfine field transferred from six next nearest neighbors in EuSe is estimated as -(25 ±2) kOe, which is comparable to a value of -24 kOe in EuTe.

Dilatometric Measurement of the Thermal Expansion of Cobalt Single Crystal

The thermal expansion of an hexagonal cobalt single crystal has been measured in the temperature range between 77 and 900 K by using a comparative quartz dilatometer. The linear coefficients of the thermal expansions along the c and a axes are 17.8×10-6 and 12.5×10-6, respectively, at 300 K and increase with increasing temperature, their rates of increase being larger at low temperatures. The temperature variations of the volume expansion and the axial ratio c/a are also derived from those of the thermal expansions.

Transferred hyperfine fields at Eu nuclei in EuSe1−xTex and EuLiH3

Abstract NMR measurements were made on transferred 153Eu hyperfine (thf) fields in EuSe1−xTex with x ⩽ 0.06 and ferromagnetic EuLiH3. The thf field in the type II antiferromagnetic state of Euse is approximately equal to that in EuTe. NMR results in EuLiH3 suggest that large positive and negative thf contributions nearly cancel in EuO.

Pressure dependences of hyperfine fields at magnetic impurities in Fe, Co and Ni

Abstract The hyperfine fields H i at various magnetic impurities in Fe and 55 Mn in Co and Ni have been measured as a function of pressure up to 10 kbar by NMR at 4.2 and 273 K. It is suggested that the pressure dependence of H i comes mainly from that of the local hyperfine field due to the impurity moment.

Hyperfine Fields at 153Eu Nuclei in Eu0.99R0.01Se (R=Sr and Sm) Studied by NMR

The 153 Eu NMR in Eu 0.99 Sr 0.01 Se and Eu 0.99 Sm 0.01 Se have been observed as a function of temperature in the range between 1.7 and 4.2 K. Each of the resonances in the magnetic phases of the NNS and NSNS types has one or two satellite lines, which are assigned to the nuclei having a Sr or Sm ion on the next nearest neighbor (n.n.n.) sites. The transferred hyperfine field per a n.n.n. Eu 2+ ion is obtained as -(4.1±0.4) kOe from the satellite NMR frequencies. The value agrees with that estimated by using the hyperfine splitting of the Eu 2+ ESR in SrSe, showing that the core polarization fields at the Eu 2+ nuclei in EuSe and SrSe are equal to each other.

Valence change of Sm ion in Eu1−xSmxSe

Abstract Crystallographic and magnetic investigations of Eu 1− x Sm x Se mixed crystals have been made. The x dependence of the lattice constant shows a deviation from the usual Vegard law and suggests an intermediate valence of Sm ions in EuSe host, which is about 2.3 for x ⩽ 0.2. The substitutive Sm ion influences magnetic properties of EuSe as a non-magnetic ion with smaller ionic radius than the Eu 2+ ion.

Pressure Dependences of the Hyperfine Fields at the 115In and 75As Impurity Nuclei in Iron

The NMR frequencies of the 115 In and 75 As impurity nuclei in ferromagnetic iron have been measured as a function of the hydrostatic pressure up to 10 kbar at 195 and 273 K. Both the 115 In and 75 As NMR frequencies decrease linearly with increasing the pressure. The pressure dependences of the hyperfine fields are obtained as ∂ln 115 H i /∂ p =-(2.25±0.05)×10 -7 bar -1 and ∂ln 75 H i /∂ p =-(9.84±0.05)×10 -7 bar -1 at 195 K. The experimental results are qualitatively discussed, together with those for other nonmagnetic impurities in iron.

Pressure dependences of the Eu hyperfine fields in Eu chalcogenides

Abstract The main and satellite 153 Eu NMR in Eu 0.99 Sr 0.01 X(X = O, S, Se) and the 151 Eu NMR in EuTe were measured as a function of pressure. The transferred hyperfine field H 2 , coming from the next nearest Eu 2+ neighbor, only weakly depends on the lattice constant. Pressure results are consistent with the chalcogen dependence of H 2 .