Zhao Tiesong

Magnetization process related to the singular point detection signal observed at high fields on Pr2Fe14B and Nd2Fe14B

Abstract The singular point detection signal, d 2 M /d t 2 , observed on Pr 2 Fe 14 B and Nd 2 Fe 14 B at high fields and low temperatures is explained on the basis of one sublattice crystal field model. The signal is attributed to a steeper reversible magnetization process and a first order magnetization process for Pr 2 Fe 14 B and Nd 2 Fe 14 B respectively.

Evaluation of exchange and crystalline field parameters in R2Fe14B compounds (R = Tb, Dy, Ho, Er and Tm)

Abstract The values of the R—Fe exchange field H ex and averaged over f and g sites CEF parameters A nm in R 2 Fe 14 B compounds (R = Tb, Dy, Ho, Er and Tm) are evaluated by fit of calculation with a series of experiments. These experiments include temperature dependences of the spontaneous magnetization M ( T ) of the compounds, magnetization curves of the compounds along [100], [110] and [001] axes at 4.2 K and at higher temperatures, the canting angle of the Ho compound, and spin reorientation temperatures T SR of Ho, Er and Tm compounds. The value of H ex of the Gd compound is also evaluated from the M ( T ) curve. The fit was restricted by the condition that the parameters vary monotonically across the R. The fitted H ex varies nearly proportional to the average of the 2nd power of the orbital radius of 4f electrons 〈 r 2 〉, and A nm nearly proportional to 〈 r n 〉 across the R. The calculation reproduces the experiments well.

Exchange and crystalline electric fields and magnetization processes in Pr2Co14B and Nd2Co14B

The values of R-Co exchange field and crystalline electric field parameters Anm in the compounds Pr2Co14B and Nd2Co14B are evaluated by fitting calculations to experiments. The experiments include the magnetization curves along the crystal axes at 4.2 and 290 K and the spin reorientation temperatures for Pr2Co14B and Nd2Co14B, and also the magnetization curves along the (100) axis at a series of temperatures between 77 and 190 K for Nd2Co14B. Amm is nearly proportional to (rn), and the sign of A40 is opposite to that for R2Fe14B. A20 decreases smoothly with increase in temperature in a similar way for Pr2Co14B and Nd2Co14B. The magnetization processes of the rare-earth and the Co sublattices are analysed.

Domain patterns of sintered NdFeB permanent magnet at different magnetized states

Abstract Domain patterns of a sintered NdFeB permanent magnet with different magnetic states in a zero applied field are observed on the pole and side surfaces of the sample using Kerr effect and Bitter technique, respectively.

Anomalous magnetic properties of Pr ions in PrxR1-xCo5 (R identical to Y,Sm)

The magnetic hyperfine fields of Pr ions in PrCo5 are measured by spin-echo NMR at 4.2 K. The magnetic properties for the PrxY1-xCo5, PrxSm1-xCo5 and DyxSm1-xCo5+0.2x compounds are analysed on the basis of the single-ion model under the assumption that rare-earth ions are triply ionized. The magnetic moment and the hyperfine fields for Pr ions in PrCo5 are calculated to be much larger than those observed in experiments, while good agreement is observed for Sm and Dy ions in SmCo5 and DyCo5.2, respectively.

Magnetisation processes of the R ions in R2Fe14B (R=Er and Tm) in a field up to 1000 kOe at 78 K

The experiment magnetisation curves M(H) of Er2Fe14B and Tm2Fe14B along the (100), (110) and (001) axes up to 550 kOe measured at 78 K are reproduced well by a calculation based on the single-ion model. The calculations shows that during the magnetisation process in such a high field both the magnetic moment and magnetic anisotropy of the R ion vary strikingly. When the field is applied along the (100) and (110) axes, both the magnetic moment and magnetic anisotropy quench at about 740 and 570 kOe for the Er and Tm ions, respectively. But when the field is applied along the (001) axis, they quench at about 570 kOe for the Tm ion while no quenching occurs for the Er ion.

Abnormal magnetic properties of the Nd ion in NdxY1−xCo5 compounds

Abstract It reveals that the calculation based on the single-ion model fails in reproducing a series of experiments for NdxY1−xCo5 compounds. The experiments include the temperature dependence of the spontaneous magnetization, the temperature dependence of the cone angle, and the magnitization curves along the crystal axes at 4.2 K. In the calculation, it was assumed that the rare-earth ions are triply ionized. If, for a satisfactory reproduction of the experiments, it is allowed that the main crystalline-electric-field parameter A20 varies with temperature, decrease of A20 with increase of temperature becomes unreasonably fast. The values of the magnetic moment of the Nd ion and the hyperfine field at the nucleous of the Nd ion were calculated, by using the fitted parameters, to be much higher than those observed in experiments. The abnormal results suggest that the Nd ion is valence fluctuated.

Crystalline electric field in NdxSm1−xCo5 compounds

Abstract The values of the crystalline-electric-field parameters and the exchange field for the Nd and Sm ions in NdxSm1−xCo5 (x = 0.00, 0.20, 0.30, 0.37, 0.50, 0.60, 0.75, 0.88 and 1.00) compounds are evaluated by comparing the calculations with experiments on a series of single crystals of the compounds. The experiments provide the following data: temperature dependence of the spontaneous magnetization, temperature dependence of the cone-angle between the magnetic easy-direction and the c-axis, and magnetization curves at different temperatures. A02 for the Sm ion decreases slightly with increase of temperature, while A02 for the Nd ion decreases apparently, which is slightly affected by the composition x. The coercivity of the domain wall movement in a crystallite during a first order magnetization process is of the intrinsic one which is intimately related to a fluctuation of the magnetic anisotropy and the exchange interaction in a microscopic scale.

Crystalline electric field at the rare-earth sites in RxY1 - xCo5 + y compounds (R = Dy and Tb)

Abstract The magnetic properties of R x Y 1 - x Co 5 + y compounds are reproduced well by a calculation based on the single-ion model. The values of the exchange field H cx and crystalline-electric-field parameters A m n at the rare-earth ion sites in R x Y 1 - x Co 5 + y (R = Dy and Tb) are evaluated by fitting the calculations to the experiments. The experiments include the temperature dependence of the spontaneous magnetization, the temperature dependence of the normalized magnetic moments of the rare-earth ions, the temperature dependence of the cone angle, the magnetization curves along the crystal axes at 4.2 K, and the hyperfine field at the Dy ion site.

NdNd exchange interaction in Nd2Fe14B

Abstract A series of intrinsic magnetic properties of Nd2Fe14B measured by previous authors are fitted by the calculations of a combined molecular-field and crystalline electric field approximation. Three sets of fitted parameters are obtained. In addition to the isotropic NdFe exchange interaction, the NdNd exchange interaction and the anisotropy of the NdFe exchange interaction are taken into account in set 1, the NdNd exchange interaction is taken into account by neglecting the anisotropy of the NdFe interaction in set 2, and both are neglected in set 3. The NdNd exchange interaction is comparable with the NdFe exchange interaction for sets 1 and 2. The value of n NdNd n NdFe is nearly the same as that obtained for Gd2Fe14B in our previous work, thus supporting the argument that the exchange interaction occur via the 4f–5d interaction. The results show that both the NdNd exchange interaction and the anisotropy of the NdFe exchange interaction need to be taken into account to obtain a reasonable explanation of the experimental results for Nd2Fe14B.