Thota S, Narang V, Nayak S, Sambasivam S, Choi B C, Sarkar T, Andersson M S, Mathieu R, Seehra M S
Department of Physics, Indian Institute of Technology, Guwahati-781039, Assam, India.
J Phys Condens Matter. 2015 Apr 29;27(16):166001. doi: 10.1088/0953-8984/27/16/166001. Epub 2015 Mar 30.
In the spinel Co2SnO4, coexistence of ferrimagnetic ordering below T(N) ≃ 41 K followed by a spin glass state below T(SG) ≃ 39 K was proposed recently based on the temperature dependence of magnetization M(T) data. Here new measurements of the temperature dependence of the specific heat C(P)(T), ac-susceptibilities χ'(T) and χ″(T) measured at frequencies between 0.51 and 1.2 kHz, and the hysteresis loop parameters (coercivity H(C)(T) and remanence M(R)(T)) in two differently prepared samples of Co2SnO4 are reported. The presence of the Co(2+) and Sn(4+) states is confirmed by x-ray photoelectron spectroscopy (XPS) yielding the structure: Co2SnO4 = [Co(2+)][Co(2+)Sn(4+)]O4. The data of C(P) versus T shows only an inflection near 39 K characteristic of spin-glass ordering. The analysis of the frequency dependence of ac-magnetic susceptibility data near 39 K using the Vogel-Fulcher law and the power-law of the critical slowing-down suggests the presence of spin clusters in the system which is close to a spin-glass state. With a decrease in temperature below 39 K, the temperature dependence of the coercivity H(C) and remanence M(R) for the zero-field cooled samples show both H(C) and M(R) reaching their peak magnitudes near 25 K, then decreasing with decreasing T and becoming negligible below 15 K. The plot of C(P)/T versus T also yields a weak inflection near 15 K. This temperature dependence of H(C) and remanence M(R) is likely associated with the different magnitudes of the magnetic moments of Co(2+) ions on the 'A' and 'B' sites and their different temperature dependence.
在尖晶石Co2SnO4中，最近基于磁化强度M(T)数据的温度依赖性，有人提出在T(N) ≃ 41 K以下存在亚铁磁有序，随后在T(SG) ≃ 39 K以下出现自旋玻璃态。本文报道了在两个不同制备的Co2SnO4样品中，对比热容C(P)(T)、在0.51至1.2 kHz频率下测量的交流磁化率χ'(T)和χ″(T)以及磁滞回线参数（矫顽力H(C)(T)和剩磁M(R)(T)）的温度依赖性进行的新测量。通过X射线光电子能谱（XPS）确认了Co(2+)和Sn(4+)态的存在，得到结构：Co2SnO4 = [Co(2+)][Co(2+)Sn(4+)]O4。C(P)与T的数据仅在39 K附近显示出自旋玻璃有序特征的拐点。使用Vogel-Fulcher定律和临界慢化的幂律对39 K附近的交流磁化率数据的频率依赖性进行分析，表明系统中存在接近自旋玻璃态的自旋团簇。随着温度降至39 K以下，零场冷却样品的矫顽力H(C)和剩磁M(R)的温度依赖性表明，H(C)和M(R)在25 K附近达到峰值，然后随T降低而减小，在15 K以下变得可以忽略不计。C(P)/T与T的关系图在15 K附近也产生了一个微弱的拐点。H(C)和剩磁M(R)的这种温度依赖性可能与“A”和“B”位点上Co(2+)离子磁矩的不同大小及其不同的温度依赖性有关。
