Ni3C nanoparticles of about 40 nm have been studied experimentally to exhibit weak ferromagnetic (FM), spin-glass (SG) and paramagnetic (PM) properties. The freezing temperature of the SG phase at zero applied field is determined as, TF0 ~ 11.0 K. At T > TF0, a very weak ferromagnetism has been observed over a PM background. The Curie temperature, TC, is shown to exceed 300 K and the ferromagnetism at 300 K is determined as about 0.02 emu/g (~6.7*10^{-4}mu_B per Ni3C formula unit) by subtracting the background paramagnetism. An anomalous dip appears in the temperature dependent coercivity, HC(T), near the freezing temperature, TF0. It reflects a distortedly reduced coercivity in the M(H) hysteresis loop measured at T = TF0 with the applied sweeping field around H = 0. This is attributable to the exchange coupling effect between the SG and the weak FM phases. The possible origin of the magnetic moments that account for the observed FM, SG and PM properties is discussed.
High-Temperature ferromagnetism from site-selective filling in (Fe,Ni)$_{6-δ}$GeTe$_2$
Yale University（耶鲁大学）；University of California, Berkeley（加州大学伯克利分校）；Lawrence Berkeley National Lab（劳伦斯伯克利国家实验室）；Cornell University（康奈尔大学）；University of Southern California（南加州大学）；Boston College（波士顿学院）
Magnetoelectric Coupling in Nickel-Cobalt Ferrite and Lanthanum Ferrite Heterostructure Composites: Experimental Evidence and Simulation-Driven Insights
Tunability of Room Temperature Ferromagnetism in Spintronic Semiconductors through Non-magnetic Atoms
通过在半导体晶格中添加磁性原子来实现和控制室温铁磁性（RTFM）是近十年来固态物理中最重要的问题之一。在这里，我们报告的第一次，据我们所知，在机制上，允许RTFM被调谐的列入\emph{non-magnetic}铝镍铁氧体。这种材料，NiFe $_{2-x}$ Al $_x$ O $_4$（x=0，0.5，1.5），已经显示出磁性半导体技术的前景，我们能够增加其多功能性的技术可行性与我们的结果。Fe原子（Fe $^{3+}$ T $_d$、Fe $^{2+}$ O $_h$和Fe $^{3+}$ O $_h$）的位置占有率和价态可以通过包含铝而有系统地控制。利用铝强烈偏好3+八面体环境的事实，我们可以选择性地用铝原子填充铁位点，从而专门调整每个铁位点的磁性贡献，因此也调整了块体材料的磁性贡献。有趣的是，铝对电子结构（补充材料）的影响很弱，允许人们在保持理想的电子特性的同时实现理想的磁特性。
