Pramanik P, Joshi D C, Reehuis M, Hoser A, Hoffmann J-U, Manna R S, Sarkar T, Thota S
Department of Physics, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India.
J Phys Condens Matter. 2020 Jun 3;32(24):245801. doi: 10.1088/1361-648X/ab71a6.
A systematic study using neutron diffraction and magnetic susceptibility is reported on Mn substituted ferrimagnetic inverse spinel Ti Mn CoO in the temperature interval 1.6 K [Formula: see text] T [Formula: see text] 300 K. Our neutron diffraction study reveals cooperative distortions of the TO octahedra in the Ti Mn CoO system for all the Jahn-Teller active ions T = Mn , Ti and Co , having the electronic configurations 3d , 3d and 3d , respectively which are confirmed by the x-ray photoelectron spectroscopy. Two specific compositions (x = 0.2 and 0.4) have been chosen in this study because these two systems show unique features such as; (i) noncollinear Yafet-Kittel type magnetic ordering, and (ii) weak tetragonal distortion with c/a < 1, in which the apical bond length d (T -O) is longer than the equatorial bond length d (T -O) due to the splitting of the e level of Mn ions into [Formula: see text] and [Formula: see text]. For the composition x = 0.4, the distortion in the T O octahedra is stronger as compared to x = 0.2 because of the higher content of trivalent Mn. Ferrimagnetic ordering in TiMnCoO and TiMnCoO sets in at 110.3 and 78.2 K, respectively due to the presence of unequal magnetic moments of cations, where Ti , Mn , and Co occupy the octahedral, whereas, Co sits in the tetrahedral site. For both compounds an additional weak antiferromagnetic component could be observed lying perpendicular to the ferrimagnetic component. The analysis of static and dynamic magnetic susceptibilities combined with the heat-capacity data reveals a magnetic compensation phenomenon (MCP) at T = 25.4 K in TiMnCoO and a reentrant spin-glass behaviour in TiMnCoO with a freezing temperature of ∼110.1 K. The MCP in this compound is characterized by sign reversal of magnetization and bipolar exchange bias effect below T with its magnitude depending on the direction of external magnetic field and the cooling protocol.
报道了一项在1.6 K [公式：见正文] T [公式：见正文] 300 K温度区间内，对Mn取代的亚铁磁性反尖晶石Ti Mn CoO进行的利用中子衍射和磁化率的系统研究。我们的中子衍射研究揭示了在Ti Mn CoO体系中，对于所有具有 Jahn-Teller 活性的离子T = Mn、Ti和Co，TO八面体的协同畸变，它们分别具有电子构型3d 、3d 和3d ，这一点通过X射线光电子能谱得到了证实。本研究中选择了两种特定的成分（x = 0.2和0.4），因为这两个体系表现出独特的特征，例如：（i）非共线的Yafet-Kittel型磁有序，以及（ii）c/a < 1的弱四方畸变，其中由于Mn离子的e 能级分裂为[公式：见正文]和[公式：见正文]，顶端键长d （T -O）长于赤道键长d （T -O）。对于成分x = 0.4，与x = 0.2相比，T O八面体中的畸变更强，这是因为三价Mn的含量更高。由于阳离子的磁矩不相等，TiMnCoO和TiMnCoO中的亚铁磁性有序分别在110.3 K和78.2 K出现，其中Ti、Mn和Co占据八面体位置，而Co位于四面体位置。对于这两种化合物，都可以观察到一个额外的弱反铁磁分量垂直于亚铁磁分量。对静态和动态磁化率以及热容量数据的分析揭示了TiMnCoO在T = 25.4 K时的磁补偿现象（MCP）以及TiMnCoO中具有约110.1 K冻结温度的再入自旋玻璃行为。该化合物中的MCP的特征是在T 以下磁化强度的符号反转和双极交换偏置效应，其大小取决于外部磁场方向和冷却过程。
