Journal of Alloys and Compounds 408–412 (2006) 177–180 High-field magnetization of single crystals of RMn 6 Ge 6-x Ga x compounds with R = Tb, Er, Tm, Yb and x ≈ 1 S. Yoshii a,∗ , K. Kindo a , C. Lef` evre b , G. Venturini b , L. Zhang c , E. Br ¨ uck c , K.H.J. Buschow c , F.R. de Boer a,c a KYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan b Lab. Chim. Sol. Min´ eral, Universit´ e Henri Poincar´ e-Nancy 1, 54506 Vandoeuvre les Nancy Cedex, France c Van der Waals-Zeeman Instituut, Universiteit van Amsterdam, 1018 XE Amsterdam, The Netherlands Available online 31 May 2005 Abstract The magnetization has been measured of single crystals of RMn 6 Ge 6-x Ga x (R = Tb, Er, Tm and Yb and x ≈ 1) compounds at 4.2 K in high magnetic fields up to 65 T applied along the main crystallographic directions. At low temperature, where the magnetocrystalline anisotropy is determined by the R contribution, these compounds exhibit easy-axis anisotropy with the c-axis as preferred moment direction. The magnetization display a variety of field-induced phase transitions which are particularly pronounced in the compounds with Tb, Er and Tm. The Yb compound exhibits the onset of a phase transition in the field region above 65T. The results are discussed in terms of the interplay between the antiferromagnetic intersublattice R–Mn coupling and the magnetic anisotropy. © 2005 Elsevier B.V. All rights reserved. Keywords: RMn 6 Ge 6-x Ga x ; High-field magnetization; Field-induced transition; Ferrimagnet; Magnetocrystalline anisotropy 1. Introduction The hexagonal HfFe 6 Ge 6 -type (P6/mmm) RMn 6 Ge 6 com- pounds, with R = Sc, Y or one of the rare-earth elements, have recently been subject of many studies [1–5]. Due to the complicated interplay between the various intra- and inter- sublattice magnetic interactions and the magnetocrystalline anisotropy of both the R and the Mn sublattice, they dis- play a wide variety of magnetic behaviour. Recently, in- vestigations of RMn 6 Ge 6-x Ga x solid solutions (R = Sc, Y, Gd–Lu) have shown that by partial replacement of Ge by Ga the ferrimagnetic state, with Curie temperatures (T C ) well above room temperature, is stabilized for all these R ele- ments [6–8]. In the compounds in which the R component does not possess a magnetic moment the Mn-sublattice mo- ment orders ferromagnetically with preferred moment di- rection perpendicular to the c-axis. If also the R compo- nent has a magnetic moment, the latter couples antipar- ∗ Corresponding author. Tel.: +81 6 6850 6687; fax: +81 6 6850 6662. E-mail address: yoshii@mag.rcem.osaka-u.ac.jp (S. Yoshii). allel to the Mn moments and imposes a strong contribu- tion to the total magnetocrystalline anisotropy upon cool- ing from room temperature to cryogenic temperatures, lead- ing to spin-reorientation transitions at intermediate temper- atures (T sr , see Table 1). The dominance of the R-sublattice anisotropy at low temperatures leads to preferred moment directions characterized by an easy axis for the compounds with R = Tb, Er, Tm and Yb and by an easy cone for R = Dy and Ho. In a recent investigation [9], we have further studied the magnetic properties of single crystals of RMn 6 Ge 6-x Ga x compounds by measurements of the magnetization at 4.2 K in high magnetic fields up to 55 T applied along the main crystallographic directions. The interplay between the anti- ferromagnetic intersublattice R–Mn coupling and the magne- tocrystalline anisotropy was found to lead to very pronounced field-induced magnetic phase transitions in the compounds with Tb, Dy, Ho, Er and Tm. The observed magnetization processes for the compounds with Tb, Er, Tm and Yb made an extension of the measurements to higher fields highly de- sirable. Therefore, these compounds have been selected for 0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.04.110