The phase relation of the ternary system Nd-Co-B quenched from 600 degrees
C in the Go-rich region has been determined by means of X-ray powder diffra
ction. In this region there exist 11 ternary borides: Nd3Co13B2, NdCo4B, Nd
5Co19B6, Nd3CO11B4, Nd2Co7B3, Nd2Co14B, NdCo12B6, NdCo4B4, Nd2Co5B3, NdCo2B
2, and Nd2Co5B2 The first five borides are members of the homologous series
Ndm+nCo5m+3nB2n (or NdCo5-xBx). New layered borides Nd3Co13B2 and Nd5Co19B
6 have not been reported previously. The space group of them is P6/mmm and
their crystal structures are refined by the Rietvled method. All the compou
nds of this Ndm+nCo5m+3nB2n family magnetically order between Te = 710 K fo
r Nd3Co13B2 and To = 330 K for Nd2Co7B3. The mean cobalt moments of the Ndm
+nCo5m+3nB2n, borides determined at 4.2 K are strongly dependent on the com
position. On the basis of the experimental results, three kinds of Co sites
with different magnetic moments are proposed. It is shown that increasing
B content in NdCo5-xBx borides leads to an increase of the second-order cry
stal-field parameters Ate, which explains the enhancement of the magnetocry
stalline anisotropy. Spin reorientations are observed in Nd3Co13B2 and Nd3C
O11B4 compounds. The magnetic phase diagram of the Ndm+nCo5m+3nB2n borides
is also given, and the behavior of magnetocrystalline anisotropy is analyze
d using the single ion model.