H. Ido

The role of boron in Rn+1Con+5B2n systems (R=Y, Sm, Dy; n=0, 1, 2, 3, and ∞)

Magnetic measurements have been made for the systems of Rn+1Co3n+5B2n (R=Y, Sm, Dy; n=1, 2, 3, 4, and ∞) in wide temperature region. The Curie temperature decreases drastically between n=0 and n=1, and slowly with n larger than 1, for all above systems. Three kinds of Co sites with different magnetic moments are proposed. The estimated Sm‐ and Dy‐atomic moments are found to be smaller than the free ion moments in the Dy system with n≥1 and in the Sm system. Magnetic anisotropy constants K1(Co) and K2(Co) have been determined at various temperatures for the Y system, and the Sm‐sublattice anisotropy constants K1(Sm) have been estimated and found to take the maximum value at n=1 and decrease with n≥1 in the Sm system. Magnetic anisotropy in the Dy system is found to be planar at all temperatures below the Curie temperature.

Magnetic transitions in Mn2−xMxSb (M=3d metals)

Magnetic and crystallographic measurements have been carried out for Mn2−xMxSb (M=Ti, V, Cr, Fe, and Co) in order to study the nature of the transition from ferrimagnetic (Fr) to antiferromagnetic (AF) states. The magnetic phase diagrams have been determined. In the cases of M=Ti and Fe, only the Fr phase is observed. In the case of M=Co, the transition between Fr and AF states is observed in the composition range of x<0.35, but for the specimens with x larger than 0.35 only the AF ordering is found. The phase diagrams obtained are discussed on the basis of the molecular field theory.

Magnetic susceptibility of RCo3B2 (R=Y, Sm, Gd, and Dy)

The temperature dependence of magnetic susceptibility has been measured in a temperature region from about 100 to 500 K for the compounds RCo3B2 with R=Y, Sm, Gd, and Dy. Their magnetization curves at T=5 K have also been measured in a pulsed high field up to 170 kOe. YCo3B2 seems to have a Pauli paramagnetic nature down to T=5 K. In the paramagnetic temperature region, SmCo3B2 exhibits Van Vleck paramagnetism; however, GdCo3B2 and DyCo3B2 show Curie–Weiss character. The paramagnetic susceptibility for all compounds mentioned above is found to include a Pauli paramagnetic contribution from the Co sublattice. In the case of GdCo3B2 at T=5 K, the magnetic moment of 0.2μB/Co, which is antiparallel to the Gd moment, is considered to be induced by the exchange field from the Gd spin. A similar induced moment of 0.14μB/Co is also estimated in DyCo3B2. The Sm‐ and Dy‐sublattice moments at T=5 K are smaller than the free‐ion values, which can be explained by the crystal‐field theory. A relatively large value of B...

Electronic structure and magnetism of YCo4B and YCo3B2

Abstract Electronic structures of YCo 4 B and YCo 3 B 2 are calculated in a self-consistent linear muffin-tin orbital method and the atomic sphere approximation. The effects of B atom in these compounds are discussed, by comparing the calculated local density-of-states curves with those of YCo 5 obtained previously. A good agreement between the calculated and observed values of the low-temperature specific heat coefficient for YCo 3 B 2 is obtained. Spin-polarized band calculations are also carried out and the local spin and orbital magnetic moments are evaluated at each Co atom site in YCo 4 B. It is found that the Co moment on 6i site is small, while the Co moment on 2c site is large. On the other hand, YCo 3 B 2 is found to be non-magnetic. These results are consistent with the observed ones and can be explained by the mixing model between 3d-states of Co and 2p-states of B.

Magnetic study of Smn+1Co3n+5B2n (n=0,1,2,3) in a pulsed high field

Abstract Hard magnetic materials, Smn+1Co3n+5B2n (n=0, …, 4) have been investigated in high magnetic fields up to 36 T at the Research Center for Extreme Materials, Osaka University. Anisotropy fields of SmCo5 (n=0), SmCo4B (n=1). Sm3Co11B4 (n=2) and Sm2Co7B3 (n=3) are found to be 710, 1200, 1160 and 1300 kOe at T=4.2K, respectively. These data are discussed together with the magnetic measurements of these compounds.

Magnetic properties of RCo4M (R=Y, Nd and Ho; M=B, Al and Ga)

Magnetic and crystallographic measurements have been made for the compounds RCo4M (R=Y, Nd, and Ho; M=B, Al, and Ga) to intercompare the magnetic properties of RCo4B, RCo4M (M=Al and Ga) and RCo5. The compounds RCo4B crystallize in the CeCo4B type structure, while RCo4M (M=Al and Ga) in the CaCu5 type. The following main conclusions have been obtained: (1) the Curie temperature and the averaged Co‐moment of RCo4M (R=Y, Nd, and Ho; M=B, Al, and Ga) are lower and smaller than those of RCo5, respectively, and 6i‐site Co‐moment in RCo4B is smaller than the 2c‐site Co‐moment by the influence of the neighboring B‐layer; (2) magnetocrystalline anisotropy of R‐sublattice of RCo4B is stronger than that of RCo5, while that of RCo4Al is remarkably weaker than that of RCo5; (3) the Co‐sublattice anisotropy constants of YCo4M (M=B and Al) are 20% or less of that of YCo5; and (4) JR‐Co and JCo‐Co, which are the exchange parameters of the atomic pairs in NdCo4M (M=B and Al), have been estimated to be JR‐Co/k ≂ 7 K and J...

Al-substitution effects on the magnetic properties of RCo5 (R=Y, Pr, Nd, and Sm)

Al substitution effects on the magnetic properties of RCo5 (R=Y, Pr, Nd, and Sm) are studied on the basis of magnetic measurements for RCo5−xAlx with x less than 2. The Al substitution considerably decreases the Curie temperature, the Co‐sublattice moment, the magnetocrystalline anisotropy of the R sublattice as well as of the Co sublattice. The Co‐sublattice moments in RCo5−xAlx have a different value depending on their directions in the crystal; in addition the rare earth moments are considerably smaller than the values of their free trivalent ions. The decrease of Co‐sublattice moment with increasing content of Al can be explained by the rigid band model, and the properties of rare earth sublattices (or atoms) mentioned above seem to be explained by the exchange field at the rare earth site which weakens with increasing Al content.

Magnetic properties of mixed crystals with NiAs‐type structure

Magnetic measurements have been carried out for the new mixed crystals such as Mn1−xTixAs (and Sb) and Cr1−xCoxSb with x ranging from 0 to 1. Mn1−xTixAs is ferromagnetic if x is less than 0.7, and the magnetic moment per Mn atom is found to be nearly constant (∼3.6 μB) for changing x. The Curie temperature TC and the asymptotic Curie temperature θp have a broad peak at around x=0.2. Mn1−xTixSb is also ferromagnetic if x is less than 0.7. The magnetic moment per Mn atom estimated from the saturation magnetization at 77 K is found to be about 10% larger than that estimated from the Curie–Weiss law above TC, but both remain nearly constant for changing x. The compounds Cr1−xCoxSb are antiferromagnetic but the detail is not clear at the present stage. The magnetic susceptibility does not obey the Curie–Weiss law for each specimen. The Neel temperature decreases on increasing x.

Magnetic properties of MnAs0.7Sb0.3 under high pressure comparison with the magnetic moment calculated for MnAs with the NiAs-type structure

Abstract The magnetization of ferromagnetic MnAs0.7Sb0.3 with the NiAs-type structure has been measured under high pressures up to 1.2 GPa and high magnetic fields up to 7 T in the temperature range from 4.2 to 270 K. The pressure dependencies of the Curie temperature and the magnetic moment are found to be very large ( d ln T C / d P=−0.35 GPa−1 and d ln M/ d P=−0.04 GPa−1) at P=0. A metamagnetic transition observed just above TC at P=0 disappears by the application of high pressure. The electronic structure of MnAs with the NiAs-type structure has been calculated by the linear muffin-tin orbital method with the atomic sphere approximation at various lattice parameters. The calculated value of the magnetization depends strongly on the lattice parameter a in the basal plane, which is consistent with the observed results of MnAs0.7Sb0.3.

Magnetic properties of RTiCo11 compounds with the ThMn12 structure

Magnetic properties of RTiCo11 (R=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er) compounds with the ThMn12 structure were investigated in the temperature range from 4.2 to 1400 K. The Curie temperatures of this series exceed 1000 K and the Co atomic moments were found to take the values ranging from 0.99 to 1.80 μB, which depend on R. The easy magnetization direction of RTiCo11 was found to be axial(c∥) for R except being planar for R=Sm and Er. This result suggests that the R sublattice with a positive Stevens factor demonstrates planar anisotropy. The Co sublattice anisotropy constant was estimated to be K1 = 7.5 × 106 erg/cc at room temperature from measurements on YTiCo11. By subtracting K1 of YTiCo11 from K1 of DyTiCo11, the anisotropy constant of the Dy sublattice was obtained to be 5.7×106 erg/cc. Spin reorientation was also observed in RTiCo11 with R=Pr, Nd and Dy, which are considered to be an axial to planar one with increasing temperature.