异金属硼镁石Cu2GaBO5和Cu2AlBO5的结构、磁性和热力学性质
Structure, magnetic and thermodynamic properties of heterometallic ludwigites: Cu2GaBO5 and Cu2AlBO5
摘要：
本文对两种Ludwi-wide族杂金属硼氧化合物Cu $_2$ GaBO $_5$和Cu $_2$ AlBO $_5$在2 K以上温度范围内的结构、磁性和热力学性质进行了广泛的研究。研究结构的显着特点是Cu和Ga/Al阳离子的选择性分布。Cu $_2$ GaBO $_5$和Cu $_2$ AlBO $_5$的晶胞中含有四个不等价的金属离子晶位。在Cu $_2$ GaBO $_5$的四个不等价晶位中，有两个晶位被Cu原子完全占据，形成沿a轴的准一维链状结构。对于Cu $_2$ AlBO $_5$，所有位置部分被Al和Cu原子占据。对低温磁化率和比热的磁贡献数据的联合分析表明，Cu $_2$ AlBO $_5$和Cu $_2$ GaBO $_5$分别在$T_{\rm N} \approx 3$和4 K处表现出反铁磁转变.两种化合物的比热的磁贡献后，减去声子的贡献。结果表明，外部磁场高于2.5 T导致的磁相变表示抑制的长程反铁磁秩序的加宽。
英文摘要：
We present an extensive study of the structural, magnetic and thermodynamic properties of high-quality monocrystals of the two heterometallic oxyborates from the ludwigite family: Cu$_2$GaBO$_5$ and Cu$_2$AlBO$_5$ 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 Cu$_2$GaBO$_5$ and Cu$_2$AlBO$_5$ contains four nonequivalent crystallographic sites of metal ions. Two sites in the structure from four nonequivalent crystallographic sites of metal ions of Cu$_2$GaBO$_5$ are fully occupied by Cu atoms which form the quasi one-dimensional chains along the a-axis. For Cu$_2$AlBO$_5$ 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 Cu$_2$AlBO$_5$ and Cu$_2$GaBO$_5$ exhibit an antiferromagnetic transition at $T_{\rm N} \approx 3$ and 4 K, respectively. The magnetic contributions to the specific heat for both compounds were obtained after subtracting the phonon contribution. It is shown that the external magnetic field above 2.5 T leads to a broadening of the magnetic phase transition indicating suppression of the long-range antiferromagnetic order.
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