The spin excitations in alpha-Cu3Mg(OH)6Br2

The two-dimensional (2D) spin-1/2 kagome model has been a subject of intense theoretical study due to its rich ground states. While many of these materials show antiferromagnetic correlations, ferromangetism is rare to find. Recently, we have successfully synthesized a new kagome material alpha-Cu3Mg(OH)6Br2, the spin arrangement along c-axis is antiferromagnetic, that within the kagome plane is ferromagnetic. The specific-heat measurement reveals an upturn behavior of the specific heat is found below 0.2 K, which can be fitted as C~T^-3/2. It is not from the nuclear Schottky anomaly or magnetic impurities since it does not move to higher temperature under magnetic fields. Instead, it is suppressed at 3 Tesla, It indicates that some exotic spin excitations present. So we propose to study the spin excitations in alpha-Cu3Mg(OH)6Br2 down to 30 mK and magnetic field up to 3 Tesla.

二维（2D）自旋1/2 kagome模型因其丰富的基态而成为理论研究的热点。尽管这类材料大多表现出反铁磁（antiferromagnetic）关联，但铁磁（ferromagnetic）现象却十分罕见。近期，我们成功合成了一种新型kagome材料α-Cu3Mg(OH)6Br2：其沿c轴的自旋排列为反铁磁，而kagome平面内的自旋排列则为铁磁。比热测量结果显示，在0.2 K以下比热呈现上升趋势，可拟合为C~T^(-3/2)。这一现象并非源于核肖特基异常或磁杂质，因为磁场作用下它并未向高温区移动；相反，在3特斯拉时该现象被抑制，表明存在某种奇异自旋激发（spin excitations）。因此，我们提议对α-Cu3Mg(OH)6Br2中的自旋激发展开研究，温度低至30毫开尔文，磁场高达3特斯拉。