Co10Ge3O16的磁结构转变、变磁性和磁相共存
Magnetostructural transition, metamagnetism, and magnetic phase coexistence in Co10Ge3O16
摘要：
Co 10 Ge 3 O 16结晶为尖晶石和岩盐交替层的共生结构。变温粉末同步辐射X射线衍射、中子衍射、磁测量和热容实验表明，在T_N = 203 K时发生了磁结构转变。这种菱面体到单斜过渡涉及CoO 6八面体沿顶轴的轻微伸长。在T_N以下，施加一个大的磁场会引起Co^2+伊辛自旋的重新取向。这种变磁性转变是一阶的，这可以通过在温度依赖性测量中观察到的潜热来证明。这一转变最初在T = 180 K时出现，在H_C = 3.9 T附近的M-H中出现一个宽的上升。在T = 120 K时，向上的转折尖锐成扭结，并出现“蝴蝶”形状，在高场引起滞后的过渡，而在低场保持线性和可逆的行为。H_C随温度的降低而降低，在T = 20 K以下，正负磁场环合并。反铁磁性用k_M =（001/2）描述，在T = 20 K以下，自发出现一个k_M =（000）的小的未补偿分量。尽管Curie-Weiss分析和离子半径表明Co ~（2+）处于高自旋态，但低温M-H在M_S = 1.0 μ B/Co时趋于饱和，我们认为场诱导态是亚铁磁体，而不是S = 1/2的铁磁体。结合其它超磁体和Co（II）体系讨论了这一不寻常的H-T相图。
英文摘要：
Co10Ge3O16 crystallizes in an intergrowth structure featuring alternating layers of spinel and rock salt. Variable-temperature powder synchrotron X-ray and neutron diffraction, magnetometry, and heat capacity experiments reveal a magnetostructural transition at T_N = 203 K. This rhombohedral-to-monoclinic transition involves a slight elongation of the CoO6 octahedra along the apical axis. Below T_N, the application of a large magnetic field causes a reorientation of the Co^2+ Ising spins. This metamagnetic transition is first-order as evidenced by a latent heat observed in temperature-dependent measurements. This transition is initially seen at T = 180 K as a broad upturn in the M-H near H_C = 3.9 T. The upturn sharpens into a kink at T = 120 K and a "butterfly" shape emerges, with the transition causing hysteresis at high fields while linear and reversible behavior persists at low fields. H_C decreases as temperature is lowered and the loops at positive and negative fields merge beneath T = 20 K. The antiferromagnetism is described by k_M = (00 1/2) and below T = 20 K a small uncompensated component with k_M = (000) spontaneously emerges. Despite the Curie-Weiss analysis and ionic radius indicating the Co2+ is in its high-spin state, the low-temperature M-H trends toward saturation at M_S = 1.0 uB/Co. We conclude that the field-induced state is a ferrimagnet, rather than a S = 1/2 ferromagnet. The unusual H-T phase diagram is discussed with reference to other metamagnets and Co(II) systems.
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