The Chemistry Department, University of Aberdeen, Meston Walk, Aberdeen, AB24 3UE, Scotland, UK.
Dalton Trans. 2018 Oct 23;47(41):14726-14733. doi: 10.1039/c8dt03071e.
The colossal magnetoresistance (CMR) observed in the oxypnictide NdMnAsO1-xFx has been further investigated. The magnetotransport is dominated by magnetopolarons. Magnetoresistance measurements of the series Nd(Mn1-xCox)AsO0.95F0.05 show that doping with cobalt on the manganese site pins the magnetopolarons and suppresses the CMR, which is completely destroyed by x = 0.047. The chemical doping results in non-stoichiometric samples, with both As and O vacancies. The relationship between the non-stoichiometry, magnetic order, electron doping and CMR is explored. The Nd antiferromagnetic transition and simultaneous reorientation of the Mn spins into the basal plane at 23 K (TSR) is not effected by Co doping. However, there is a significant decrease in TN(Mn) as the antiferromagnetic transition is suppressed from 360 K to 300 K as x increases from 0-0.047. The manganese moment at 10 K is also reduced from 3.86(2)μB to 3.21(2)μB over the same doping range. This reduction in the in-plane Mn moment decreases the electron-electron correlations below TSR and acts to further diminish the magnetoresistance.
在氧磷化物 NdMnAsO1-xFx 中观察到的巨大磁电阻 (CMR) 进一步得到了研究。磁输运主要由磁极化子主导。对系列 Nd(Mn1-xCox)AsO0.95F0.05 的磁电阻测量表明，锰位掺杂钴会固定磁极化子并抑制 CMR，当 x = 0.047 时 CMR 完全被破坏。化学掺杂导致非化学计量的样品，同时存在 As 和 O 空位。探讨了非化学计量、磁有序、电子掺杂和 CMR 之间的关系。Nd 反铁磁转变和 Mn 自旋在 23 K 时同时进入基面的重新定向（TSR）不受 Co 掺杂的影响。然而，随着 x 从 0 增加到 0.047，反铁磁转变从 360 K 抑制到 300 K，TN(Mn) 显著降低。在相同的掺杂范围内，10 K 时的锰磁矩也从 3.86(2)μB 降低到 3.21(2)μB。TSR 以下的平面内 Mn 磁矩的减小降低了电子-电子相关性，并进一步减小了磁电阻。
