HIGH-FIELD MAGNETIZATION PROCESS AND CRYSTALLINE FIELD IN R2Co14B

Magnetizations of R2Co14B single crystals with R = Nd and Pr have been measured under steady magnetic fields up to 300 kOe. We have shown that the observed data can be well reproduced by nearly the same set of crystalline field and R-3d exchange parameters as that in R2Fel4B system. Since the discovery of NdzFelsB, a wide variety of magnetization curves in high fields has been observed for different R2Fel4B (R denotes a rare-earth element) compounds [I]. We have shown recently [2] that all these observations can be explained systematically by a simplified Harniltonian which takes account of, at each R site, the crystalline electric field (CEF) and the molecular field due to the Fe-R exchange interaction. This success comes from the fact that, in this system, the Fe-Fe exchange interaction is so strong as compared with the Fe-R exchange that we can assume the Fe sublattice is "rigid" and therefore not affected by the R ion. The same situation occurs in the R2Co14B system. According to the magnetic measurement of LazColrB single crystal 131, the Co sublattice is expected to favor the easy c-plane for the spontaneous magnetization, in contrast to the Fe sublattice in R2Fel4B. When an R sublattice in R2Co14B favors the c-axis, a spin reorientation from the c-axis to cplane takes place at high temperature owing to the Co contribution. We report here the experimental results of high-field magnetization process in R2Co14B with R = Nd, Pr at 4.2 K and 290 K, where the Co contribution to the magnetic anisotropy is insignificant, and compare them with the calculations using a similar method to that described above. Single crystals of NdzColrB and Pr2Co14B were embedded respectively into a cube of epoxy resin with the edges parallel to the principal crystallographic directions. Magnetizations have beem measured by the vibrating-sample method or the sample extraction method in steady magnetic fields up to 300 kOe generated by a hybrid magnet system. Conventional pulsedfield method was used for higher field measurements. Observed magnetization curves of NdzCol4B a t 4.2 K and 290 K are shown in figure la. At 4.2 K the magnetization along the [loo] direction shows a sudden jump [4] at about 210 kOe, which manifests the first order magnetization process (FOMP) observed also in NdzFe~rB. 4t 290 K magnetizations along both [loo] and [I101 directions saturate above about 80 kOe, although the saturation values are slightly smaller than the easy direction value. This anisotropy of saturation values has also been observed in NdzFel4B. In the case of Pr2C014B, observed magnetization ( a ) OBSERVATION Nd2C014B CALCULATION I ( ) OBSERVAT l ON Pr2C0148 CALCULATION