Iron oxides are among the most abundant materials on Earth, and yet there are some of their basic properties which are still not well-established. Here, we present temperature-dependent magnetic, X-ray, and neutron diffraction measurements refuting the current belief that the magnetic ordering temperature of ε-Fe₂O₃ is ∼500 K, i.e., well below that of other iron oxides such as hematite, magnetite, or maghemite. Upon heating from room temperature, the ε-Fe₂O₃ nanoparticles’ saturation magnetization undergoes a monotonic decrease while the coercivity and remanence sharply drop, virtually vanishing around ∼500 K. However, above that temperature the hysteresis loops present a nonlinear response with finite coercivity, making evident signs of ferrimagnetic order up to temperatures as high as 850 K (T_N1). The neutron diffraction study confirms the presence of ferrimagnetic order well above 500 K with Pna'2₁' magnetic symmetry, but only involving two of the four Fe³⁺ sublattices which are ordered below T_N2 ≈ 480 K, and with a reduced net ferromagnetic component, that vanishes at above 850 K. The results unambiguously show the presence of a high-temperature magnetic phase in ε-Fe₂O₃ with a critical temperature of T_N1 ∼ 850 K. Importantly, this temperature is similar to the Curie point in other iron oxides, indicating comparable magnetic coupling strengths. The presence of diverse magnetic phases is further supported by the nonmonotonic evolution of the thermal expansion. The existence of a high-temperature ferrimagnetic phase in ε-Fe₂O₃ may open the door to further expand the working range of this multifunctional iron oxide.

中文翻译：

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推出一个新的高温序磁相ε-铁₂ Ø ₃

氧化铁是地球上最丰富的材料之一，但是其中一些基本特性尚未得到充分确立。在这里，我们当前温度依赖性磁性，X射线，和中子衍射测量驳当前认为的磁有序温度ε -铁₂ ö ₃是〜500 K，即，远低于其他氧化铁如赤铁矿的，磁铁矿或磁赤铁矿。当从室温加热时，ε-的Fe ₂ ö ₃纳米粒子的饱和磁化强度发生单调下降，而矫顽力和剩磁急剧下降，大约在500 K附近消失。但是，在该温度以上，磁滞回线呈现出具有有限矫顽力的非线性响应，从而在高温下形成明显的亚铁磁序迹象。为850 K（T _N1）。中子衍射研究证实铁磁顺序的存在大大高于500 K的PNA “2 ₁ ”磁对称性，但仅涉及两个四个的Fe ³⁺亚晶格哪个是有序的下面Ť _N2≈480 K，并具有减少的净铁磁部件，即消失在高于850 K.结果明确地显示了在高温磁性相的存在ε-的Fe ₂ ö ₃与的临界温度Ť _N1〜850 K.重要的是，该温度类似于其他氧化铁中的居里点，表明具有相当的磁耦合强度。热膨胀的非单调演变进一步支持了多种磁性相的存在。在ε -铁的高温铁磁相的存在₂ ö ₃可打开门，进一步扩大该多功能氧化铁的工作范围。