Neutron spectroscopy is used to probe transverse acoustic phonons near the (2, 2, 0) Bragg position in colossal magnetoresistive La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3. Upon warming to temperatures near Tc = 257 K the phonon peaks in La0.7Ca0.3MnO3 soften and damp significantly with the phonon half width at half maximum approaching 2.5 meV for phonons at a reduced wave vector of q = (0.2, 0.2, 0). Concurrently a quasielastic component develops that dominates the spectrum near the polaron position at high temperatures. This quasielastic scattering is ~5 times more intense near Tc than in La0.7Sr0.3MnO3 despite comparable structural distortions in the two. The damping becomes more significant near the polaron position with a temperature dependence similar to that of polaron structural distortions. An applied magnetic field of 9.5 T only partially reverses the damping and quasielastic component, despite smaller fields being sufficient to drive the colossal magnetoresistive effect. The phonon energy, on the other hand, is unaffected by field. The damping in La0.7Sr0.3MnO3 near Tc at a reduced wave vector of q = (0.25, 0.25, 0) is significantly smaller but displays a similar trend with an applied magnetic field.
Magnetic field dependent variable range hopping behaviour in resistivity at low temperatures in polycrystalline colossal magnetoresistive manganites: evidence of spin polarised tunnelling
Mesoscale magnetism at the grain boundaries in colossal magnetoresistive films
我们报道了在外延La $_{1-x}$ Sr $_{x}$ MnO $_{3}$薄膜中发现的具有独特磁性的介观区域，这些区域表现出穿过晶界的隧道状磁电阻。通过使用温度依赖的磁力显微镜，我们观察到的中尺度区域形成的晶界附近，并具有不同的居里温度（高达20 K { \it高}）比晶粒内部。我们的图像提供了直接的证据，以前的猜测，在薄膜的晶界不是磁性和电子尖锐的接口。中尺度区域的大小随温度和底层缺陷的性质而变化。
Colossal electroresistance and colossal magnetoresistive step in paramagnetic insulating phase of single crystalline bilayered manganite(La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$
我们报告了在（La $_{0.4}$ Pr $_{0.6}$）$_{1.2}$ Sr $_{1.8}$ Mn $_{2}$ O $_{7}$的顺磁绝缘（PMI）状态下在$ab$ -平面上施加电流引起的低温电阻的显著降低。在较低的温度下观察到一个巨大的电阻效应，达到~ 95%。在低于10 K的低温下，在5 T附近出现一个巨大的磁阻阶跃，并伴随着绝缘体-金属转变的超尖锐宽度。向晶体注入更高的电流会导致阶跃跃迁消失。这些发现与研究晶体的PMI矩阵内钉扎的短程电荷有序簇的存在有密切的关系。
Ultrafast collective dynamics of short-range charge/orbital ordering fluctuations in colossal magnetoresistive oxides
巨磁电阻锰氧化物是一种自旋、电荷、轨道和晶格自由度之间存在强耦合的高关联系统，导致复杂的相图和多种有序形式的共存。例如，MnO $_{6} octahedra in CMR manganites and compete with the electron itinerancy favored by double exchange. However, access to the ordered dynamical state has been challenging, mostly due to intrinsic experimental difficulties in measuring fast short-range correlations. Here, we report on a strongly damped low-energy collective mode originating from fast short-range CO fluctuations in La}$ _{0.67}Ca $_{0.33}Mn{O}$ _{3}（LCMO）单晶和薄膜的纳米级电荷/轨道有序（CO）涨落似乎与Jahn-Teller（JT）畸变协同作用。我们阐明了集体模式的色散关系和依赖于平均A位离子半径，r$_{A}，和空穴掺杂浓度。我们的研究结果表明，第一次CMR锰氧化物中的动态…
Using a two-band double-exchange model with Jahn-Teller lattice distortions and super-exchange interactions, supplemented by quenched disorder, at electron density $n=0.65$, we explicitly demonstrate the coexistence of the $n$ = 1/2-type ($π, π$) charge-ordered and the ferromagnetic nanoclusters above the ferromagnetic transition temperature $T_{\rm c}$ in colossal magnetoresistive (CMR) manganites. The resistivity increases due to the enhancement of the volume fraction of the charge-ordered and the ferromagnetic nanoclusters with decreasing the temperature down to $T_{\rm c}$. The ferromagnet…
Manganites are famous mostly for the colossal magnetoresistive effect, which involves the phase separation between ferromagnetic phase and charge-ordered CE-type antiferromagnetic phases. Furthermore, manganites contain some typical magnetic ferroelectrics, e.g. E-type antiferromagnetic $o$-HoMnO$_3$. Here we re-examined these zigzag-winding antiferromagnetic phases (CE-type and E-type antiferromagnets) from the topological perspective. Our theoretical analysis proved that the E-type phase is a weak topological insulator belonging to the $\mathbb{Z}$ class. In momentum space, we classify the s…
While the spin dynamics of La$_{0.7}$Ca$_{0.3}$MnO$_3$ in the ferromagnetic phase are known to be unconventional, previous measurements have yielded contradictory results regarding the damping of spin wave excitations. Neutron spectroscopy measurements on a sample with a transition temperature of $T_c$=257 K, higher than most single crystals, unambiguously reveal an anomalous increase in spin wave damping for excitations approaching the Brillouin zone boundary along the [$100$] direction that cannot be explained as an artifact due to a noninteracting phonon branch. Spin waves throughout the ($…
Extrinsic inhomogeneity effects in magnetic, transport and magnetoresistive properties of La_{1-x}Ca_{x}MnO_{3} (x\approx 0.33) crystal prepared by the floating zone method
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。
The origin of the effect of colossal magneto-resistance (CMR) remains still unexplained. In this work we revisit the spin dynamics of the pseudo-cubic La1-xSrxMnO3 along the Mn-O-Mn bond direction at four x doping values (x < 0.5) and various temperatures and report a new lattice dynamics study at x0=0.2, representative of the optimal doping for CMR. We propose an interpretation of the spin dynamics in terms of orbital polarons. This picture is supported by the observation of a discrete magnetic energy spectrum Enmag (q) characteristic of the internal excitations of "orbital polarons" defined …
Spin-polarized tunneling spectroscopic studies of the intrinsic heterogeneity and pseudogap phenomena in colossal magnetoresistive manganite La_{0.7}Ca_{0.3}MnO_{3}
Colossal magnon-phonon coupling in multiferroic Eu$_{0.75}$Y$_{0.25}$MnO$_3$
本文报道了Eu $_{0.75}$ Y $_{0.25}$ MnO $_3$的变温远红外光谱（10-250 cm $^{-1}$）的磁诱导电偶极吸收谱。这些光谱只发生在$e||a$极化中，由两个相对窄的电磁子特征和一个宽的吸收带组成，其中电磁子特征在$T_{FE}=30$ K开始，而吸收带在远高于$T_N=47$ K的温度下持续存在。所观察到的激发占步的静态介电常数在铁电相。观测到80 cm $^{-1}$处的电磁振子与附近的最低光学声子强耦合，该声子将其光谱重量的1/2以上转移到磁振子。我们把宽背景吸收的起因归结为声子的两个磁振子发射衰变过程。
Among colossal magnetoresistive manganites the prototypical ferromagnetic manganite La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ has a relatively small magnetoresistance, and has been long assumed to have only weak electron-lattice coupling. Here we report that La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ has strong electron-phonon coupling: Our neutron and x-ray scattering experiments show strong softening and broadening of transverse acoustic phonons on heating through the Curie temperature T$_C$ = 350 K. Simultaneously, we observe two phases where metallic resistivity and polarons coexist. The ferromagnetic polaronic me…
Role of Oxygen Electrons in the Metal-Insulator Transition in the Magnetoresistive Oxide La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ Probed by Compton Scattering
Influence of magnetic field on paramagnetic-ferromagnetic transition in La$_{1-x}$Ca$_{x}$MnO$_{3}$ ($x\approx 0.25$) crystal: ultrasonic and transport studies
We report the temperature and magnetic field dependence of transport properties in epitaxial films of the manganite La$_{1-x}$Ca$_{x}$MnO$_{3}$ in the overdoped region of the phase diagram for $x > 0.5$, where a charge--ordered (CO) and an antiferromagnetic (AF) phase are present. Resistivity, magnetoresistance and angular dependence of magnetoresistance were measured in the temperature interval $4.2 ~\mathrm{K} < T < 300 ~\mathrm{K}$, for three concentrations $x = 0.52, 0.58$ and $0.75$ and in magnetic fields up to 5 T. The semiconductor/insulator--like behavior in zero field was observed in …
