Measurements of the magnetization M as a function of temperature (5 K - 300 K) and applied magnetic field H (up to 50 kOe) in 30 A particles of FeOOH are reported. M increases with decreasing T, peaking at T_B approx approx 65 K below which the ZFC (zero-field-cooled) and the FC (field-cooled) data separate. Hysteresis loop measured at 10 K for ZFC shows an open loop up to 40 kOe with coercivity approx approx 2 kOe. For the FC case, the loop shifts and the loop-shift increases with the cooling field H_c, approaching saturation above H_c appro approx 20 kOe. From the variation of M vs H above T_B, a magnetic moment/particle mu _p approx approx 300 mu _B is determined. These results suggest that the FeOOH nanoparticles have an antiferromagnetically ordered core with uncompensated surface spins yielding mu _p and the surface spins order in a spin-glass-like state below T_B, possibly due to interparticle interactions.
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机译：报道了在30 A FeOOH颗粒中磁化强度M与温度（5 K-300 K）和施加的磁场H（最大50 kOe）的关系。 M随着T的减小而增加，在大约65 K的T_B处达到峰值，在此以下ZFC（零场冷却）和FC（场冷却）数据分开。 ZFC在10 K下测得的磁滞回线显示了一个开环，最高可达40 kOe，矫顽力约为2 kOe。对于FC情况，回路位移和回路位移随冷却场H_c的增加而增加，在H_c之上接近饱和，约为20 kOe。根据T上的M vs H的变化，确定磁矩/粒子mu _p大约为300 mu _B。这些结果表明，FeOOH纳米粒子具有反铁磁有序的核，其未自旋的表面自旋产生mu _p，并且表面自旋在T_B以下呈类似自旋玻璃态的自旋有序，这可能是由于粒子间的相互作用。
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