Kazuyoshi Ichinose

Hyperfine Fields at 89Y Nuclei in Y(Fe1-xTx)2 (T=V, Mn, Co, Ni, Al) with Low Concentrations x

NMR of 89 Y nuclei in Y(Fe 1- x T x ) 2 (T=V, Mn, Co, Ni, Al) has been observed at 4.2 K. Well-resolved satellite structures of Y resonance appear in these compounds. This shows that the Y hyperfine field is mainly due to the magnetic nearest neighbor atoms. The magnetic moment of T atoms is estimated by two methods: (i) the contribution of T atoms to the hyperfine field is proportional to the magnetic moments of Fe and T atoms and (ii) the well known empirical relation between the hyperfine field and the mean magnetic moment of alloys is used. These results are in good agreement with those in dilute T–Fe alloys except for T=Mn. The intensity ratio of satellite peaks is discussed based upon a statistical distribution of Fe and T atoms.

Magnetic properties of Y(Co1−xTx)2-hydrides (T = Ni, Al)

Magnetization measurements have been performed on the hydrides Y(Co1−xTx)2Hy (T = Ni, Al) at 4.2 K. In all hydrides, ferromagnetism has been observed. The occurrence of ferromagnetism in the hydrides may be ascribed to a lattice expansion ( = 7%) by hydrogen absorption and an electron transfer.

The magnetic properties of GdCo2 compound and its hydrides

The measurements of the magnetization and the hyperfine fields at 59 Co nuclei were performed in GdCo 2 and its hydrides (GdCo 2 H y ). The results of the magnetization measurement show that hydrogen absorption leads to a drastic reduction (46–77%) in the magnetic moment per Co atom. This reduction can be interpreted as due to two contributions. The one is an electron transfer in the direction H atom→Co atom and the other is a change of the exchange interaction on the Co atom. On the other hand, the hyperfine fields at 59 Co nuclei undergo a smaller reduction (18–21%) as compared with a change in the Co moment upon hydrogen absorption. This reduction is discussed in terms of contributions of nearest neighbour Co and Gd atoms to the own Co atom.

1H NMR study of YT2-hydride (T = Fe, Mn)

Abstract In the hydrides YMn 2 H 3.0 , the nuclear magnetic resonance of 1 H nuclei has been measured under external fields up to 50 kOe at 4.2 K and three 1 H NMR signals have been observed. The 1 H hyperfine fields corresponding to these NMR signals can be discussed in terms of the dipole interaction between the H nuclei and the localized moments of the Mn(or Fe) atoms surrounding H atoms.

Spin reorientations in (Nd1-xYx)2Co14B compounds

Abstract Magnetization measurements and 59 Co NMR have been performed for (Nd 1− x R x ) 2 Co 14 B(R=Y, Pr, Sm, Gd and Tb) compounds. Three types of the spin phase diagrams, depending on the sign of the Stevens factor of the R ion, have been established based on these measurements. The results are discussed with the crystalline electric field (CEF) approximation.

NMR Study of Gd(T1-xCox)2 (T=Mn, Fe, Ni, Al)

Nuclear magnetic resonances of 59 Co, 55 Mn, 27 Al, 155 Gd and 157 Gd nuclei in Gd(T 1- x Co x ) 2 (T=Mn, Fe, Ni, Al) compounds at 4.2 K have been observed for 0≦ x ≦1. From the analysis of these NMR spectra, the concentration dependence of 59 Co hyperfine field is found to be proportional to the sum of the conduction electron polarization arising from nearest neighbor T atoms, and shown that Co atoms carry a magnetic moment induced by the neighboring T atoms. The hyperfine coupling constants of the core polarization in Gd(T 1- x Co x ) 2 compounds have been estimated to be larger than those of conduction electron polarization for T=Ni and Al, whereas they are comparable for T=Fe, and are complicated for T=Mn. These results are analyzed in a local environment model.

NMR Study of 59Co in Gd1-xYx (Fe.7Co.3)2 and Gd1-xYx (Fe.5Co.5)2

Nuclear magnetic resonance of 59 Co nuclei in Gd 1- x Y x (Fe .7 Co .3 ) 2 and Gd 1- x Y x (Fe .5 Co .5 ) 2 has been observed at 77 K as a function of Y concentration. The contribution of 4f electrons of Gd atoms to the hyperfine fields is estimated as at most 10 kOe in these two systems. This value is interpreted as the sum of the change in three kinds of contributions caused by Y substitution; the core polarization in the central Co atom, the conduction electron polarization arising from nearest neighbor Fe and Co atoms and the transferred hyperfine field from neighboring Gd atoms. The temperature dependence of resonance frequencies in Gd(Fe .7 Co .3 ) 2 and Gd(Fe .5 Co .5 ) 2 has also been measured.

Magnetic properties of Sm2(Co1−xTx)14B (T = Mn, Fe, Ni)

The 59 Co NMR and magnetic measurements in Sm 2 (Co 1− x T x ) 14 B (T = Mn, Fe, Ni) have been carried out at 4.2 and 77 K, respectively. The 59 Co hyperfine fields in Sm 2 (Co 1− x T x ) 14 B increase for T = Fe, and decrease for T = Mn, Ni with increasing T-concentration. These results show that the 59 Co hyperfine fields depend on nearest neighbor T atoms.

NMR Study of ^ Al in (Gd_1-xTb_x) Al_2

Nuclear magnetic resonance of 27 Al nuclei in (Gd 1- x Tb x )Al 2 has been observed at 4.2 K as a function of Tb concentration. Two peaks are observed and their positions decrease almost linearly with Tb concentration, indicating that the gadolinium moment direction does not change all over the concentration. The transferred hyperfine fields from rare earth ions in these compounds are analysed from RKKY theory.

NMR study of R(Fe1-xCox)3-hydride

Abstract The NMR signals of 59Co in R(Fe1-xCox)3Hy (R = Y, Gd) were measured by the spin echo method at 77 K. The results show that the hyperfine fields at 59Co nuclei of CoI and CoIII sites decrease and the hyperfine field at 59Co nuclei of CoII site increases upon hydrogen absorption.