Abstract We present an extensive study of the structural, magnetic and thermodynamic properties of high-quality monocrystals of two heterometallic oxyborates from the ludwigite family: Cu2GaBO5 and Cu2AlBO5 in the temperature range above 2 K. The distinctive feature of the investigated structures is the selective distribution of Cu and Ga/Al cations. The unit cell of Cu2GaBO5 and Cu2AlBO5 contains four nonequivalent crystallographic sites of metal ions. Two sites in the structure of Cu2GaBO5 are fully occupied by Cu atoms which form the quasi one-dimensional chains along the a-axis. For Cu2AlBO5 all sites are partially occupied by Al and Cu atoms. The joint analysis of low-temperature data on magnetic susceptibility and magnetic contribution to the specific heat showed that Cu2AlBO5 and Cu2GaBO5 exhibit an antiferromagnetic transition at T N = 2.4 and 4.1 K, respectively. The magnetic response below T N can be represented as the sum of two contributions: the ordered component and the paramagnetic contribution from defects of the same relative weight. It is shown that the external magnetic field above 2.5 T and 2.8 T for Cu2GaBO5 and Cu2AlBO5, respectively, leads to a broadening of the magnetic phase transition indicating suppression of the long-range antiferromagnetic order.

中文翻译：

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异金属铝矾土的结构、磁性和热力学性质：Cu2GaBO5 和 Cu2AlBO5

摘要 我们广泛研究了 2 K 以上温度范围内的两种来自 ludwigite 家族的异金属氧硼酸盐：Cu2GaBO5 和 Cu2AlBO5 的高质量单晶的结构、磁性和热力学性质。所研究结构的显着特征是选择性分布Cu 和 Ga/Al 阳离子。Cu2GaBO5 和 Cu2AlBO5 的晶胞包含四个不等价的金属离子晶位。Cu2GaBO5 结构中的两个位点被 Cu 原子完全占据，Cu 原子沿 a 轴形成准一维链。对于 Cu2AlBO5，所有位点都被 Al 和 Cu 原子部分占据。对磁化率和磁对比热的贡献的低温数据的联合分析表明，Cu2AlBO5 和 Cu2GaBO5 在 TN = 2 时表现出反铁磁转变。分别为 4 和 4.1 K。低于 TN 的磁响应可以表示为两个贡献的总和：有序分量和来自相同相对重量的缺陷的顺磁贡献。结果表明，对于 Cu2GaBO5 和 Cu2AlBO5，分别高于 2.5 T 和 2.8 T 的外部磁场导致磁相变加宽，表明长程反铁磁有序受到抑制。