Colossal magnetoresistance in EuZn$_2$P$_2$ and its electronic and magnetic structure
Sarah Krebber, Marvin Kopp, Charu Garg, Kurt Kummer, Jörg Sichelschmidt, Susanne Schulz, Georg Poelchen, Max Mende, Alexander V. Virovets, Konstantin Warawa, Ma… 展开作者
Sarah Krebber, Marvin Kopp, Charu Garg, Kurt Kummer, Jörg Sichelschmidt, Susanne Schulz, Georg Poelchen, Max Mende, Alexander V. Virovets, Konstantin Warawa, Mark D. Thomson, Artem V. Tarasov, Dmitry Yu. Usachov, Denis V. Vyalikh, Hartmut G. Roskos, Jens Müller, Cornelius Krellner, Kristin Kliemt
We investigate single crystals of the trigonal antiferromagnet EuZn$_2$P$_2$ ($P\overline{3}m1$) by means of electrical transport, magnetization measurements, X-ray magnetic scattering, optical reflectivity, angle-resolved photoemission spectroscopy (ARPES) and ab-initio band structure calculations (DFT+U). We find that the electrical resistivity of EuZn$_2$P$_2$ increases strongly upon cooling and can be suppressed in magnetic fields by several orders of magnitude (CMR effect). Resonant magnetic scattering reveals a magnetic ordering vector of $q = (0\, 0\, \frac{1}{2})$, corresponding to an $A$-type antiferromagnetic (AFM) order, below $T_{\rm N} = 23.7\,\rm K$. We find that the moments are canted out of the $a-a$ plane by an angle of about $40^{\circ}\pm 10^{\circ}$ degrees and aligned along the [100] in the $a-a$ plane. We observe nearly isotropic magnetization behavior for low fields and low temperatures which is consistent with the magnetic scattering results. The magnetization measurements show a deviation from the Curie-Weiss behavior below $\approx 150\,\rm K$, the temperature below which also the field dependence of the material's resistivity starts to increase. An analysis of the infrared reflectivity spectrum at $T=295\,\rm K$ allows us to resolve the main phonon bands and intra-/interband transitions, and estimate indirect and direct band gaps of $E_i^{\mathrm{opt}}=0.09\,\rm{eV}$ and $E_d^{\mathrm{opt}}=0.33\,\rm{eV}$, respectively, which are in good agreement with the theoretically predicted ones. The experimental band structure obtained by ARPES is nearly $T$-independent above and below $T_{\rm N}$. The comparison of the theoretical and experimental data shows a weak intermixing of the Eu 4$f$ states close to the $Γ$ point with the bands formed by the phosphorous 3$p$ orbitals leading to an induction of a small magnetic moment at the P sites.
Multi-scale Phase Modulations in Colossal Magnetoresistance Manganites
大量的实验结果提出了在锰氧化物的巨磁电阻观测到的多尺度相位调制现象。两个关键类型的相位不均匀性直接相关的庞磁电阻（CMR）进行了讨论。第一种类型涉及结构和电子不同相的微米级共存。我们提出了广泛的实验数据的原型系统表现出这样的相共存，（La，Pr）$_{5/8}$ Ca $_{3/8}$ MnO $_{3}$。这些数据表明，在该系统中的金属-绝缘体转变的弛豫输运现象起着关键作用，并在很大程度上负责显着的磁电阻的大小。多相态的相组成受电子关联和马氏体调节应变的影响。第二种类型的非均匀状态是在高温下通常在锰氧化物中发现的顺磁状态中实现的。在这种状态下，纳米级的结构相关性与纳米级的电荷/轨道有序区域进行观察。众多的锰氧化物系统的实验研究表明，这些相关性是通用的正交混合价锰氧化物，相关区域的CMR效应中起着至关重要的作用。
REPLY to Comments on "Giant Dielectric Response in the One-Dimensional Charge-Ordered Semiconductor (NbSe4)3I" and "Colossal Magnetocapacitance and Colossal Magnetoresistance in HgCr2S4" (cond-mat/0607500)
Magnetic field dependent variable range hopping behaviour in resistivity at low temperatures in polycrystalline colossal magnetoresistive manganites: evidence of spin polarised tunnelling
Comment on ``Spin Dependent Hopping and Colossal Negative Magnetoresistance in Epitaxial $Nd_{0.52}Sr_{0.48}MnO_{3}$ Films in Fields up to 50 T''
最近，Wagner等人[Phys. Rev. Lett. Vol.81，P.3980（1998）]建议修改Mott的原始模型以并入跳跃势垒，该跳跃势垒取决于在基元过程中初始和最终状态的电子自旋之间的取向差。他们进一步声称，使用该模型，他们可以解释观察到的缩放行为-负磁阻缩放比例的布里渊函数$\cal{B}$在铁磁状态和${\cal{B}}^2$在顺磁状态。在这篇评论中，我们认为，莫特的原始模型所需的修改是不同的瓦格纳等人提出的，并进一步表明，我们的图片将成功地解释所观察到的缩放在两个制度。
Colossal magnetoresistance in a nonsymmorphic antiferromagnetic insulator
本文研究了反铁磁Eu $_{5}$ In $_{2}$ Sb $_{6}$的非对称Zintl相。我们的电输运数据表明，Eu $_{5}$ In $_{2}$ Sb $_{6}$是显着的绝缘，并表现出异常大的负磁阻，这是一致的磁极化子的存在。从{ \it ab initio}计算，在广义梯度近似（GGA）下，Eu $_{5}$ In $_{2}$ Sb $_{6}$的顺磁态是拓扑非平凡的半金属，而使用修正的Becke-Johnson势得到了具有平凡拓扑指数的绝缘态.值得注意的是，GGA+U计算表明Eu $_{5}$ In $_{2}$ Sb $_{6}$的反铁磁相可能具有轴子绝缘态。我们的研究结果提供了重要的反馈理论的拓扑分类和突出的潜力，实现清洁的磁窄隙半导体Zintl材料。
Anisotropy of the magnetic and transport properties in EuZn$_2$As$_2$
最近的几项研究表明，\ECA \的磁结构的各向异性在稳定外尔结方面起着重要作用。为了研究磁各向异性与Weyl物理之间的关系，我们对EuZn $_2$ As $_2$和EuCd $_2$ As $_2$进行了比较研究.我们进行了结构分析，电子输运，和磁化实验的毫米级单晶的EuZn $_2$ As $_2$，并比较结果的EuCd $_2$ As $_2$。结合第一性原理计算和中子衍射实验，我们确定了EuZn $_2$ As $_2$的磁基态为A型反铁磁有序，其转变温度（$T_\mathrm{N}$ = 19.6 K）是EuCd $_2$ As $_2$的2倍.与EuCd $_2$ As $_2$一样，EuZn $_2$ As $_2$的负磁电阻在随电场增加而抑制$T_\mathrm{N}$处的电阻率峰之后被观察到。然而，在EuZn $_2$ As $_2$中，输运和磁化的各向异性都大大降低。电子能带计算表明，这种差异可能是由于锌化合物中较弱的自旋-轨道耦合、更局域化的$d$ -轨道以及Eu $s$ -轨道的较大贡献。相同的能带结构效应也可能导致在EuZn $_2$ As $_2$中观察到比EuCd $_2$ As $_2$更小的非线性异常霍尔效应。
Electronic and Magnetic Properties of the Interface between a doped cuprate Y0.6Pr0.4Ba2Cu3O7 and a colossal-magnetoresistance manganite La2/3Ca1/3MnO3
Photoemission and x-ray absorption spectroscopy study of electron-doped colossal magnetoresistance manganite: La0.7Ce0.3MnO3 film
利用光电子能谱（PES）和X射线吸收谱（XAS）研究了La_（0.7）Ce_（0.3）MnO_3（LCeMO）薄膜的电子结构。LCeMO的Ce 3d芯能级PES和XAS谱与CeO 2的非常相似，表明Ce离子远不是三价的。在Ce 4 d $\to$ 4 f吸收边附近观察到很弱的4 f共振，表明Ce 4 f局域态在基态几乎为空. Mn 2 p XAS谱显示了Mn（2+）多重态的存在，证实了LCeMO中Mn离子的Mn（2+）-Mn（3+）混合价态。测得的LCeMO的Mn 3d PES/XAS光谱与使用LSDA+U方法计算的Mn 3d PDOS相当吻合。LSDA+U计算预测了LCeMO的半金属基态。
