The ferrimagnetic insulator Mn3Si2Te6, which features a Curie temperature Tc at 78 K and a delicate yet consequential magnetic frustration, exhibits colossal magnetoresistance (CMR) when the magnetic field is applied along the magnetic hard axis, surprisingly inconsistent with existing precedents [Y. Ni, H. Zhao, Y. Zhang et al. Phys. Rev. B 103, L161105 (2021)]. This discovery motivates a thorough single-crystal neutron diffraction study in order to gain insights into the magnetic structure and its hidden correlation with the new type of CMR. Here we report a noncollinear magnetic structure below the Tc where the moments lie predominantly within the basal plane but tilt toward the c axis by ~10o at ambient conditions. A substantial magnetic diffuse scattering decays slowly and persists well above the Tc. The evolution of the spin correlation lengths agrees well with the electrical resistivity, underscoring the role of spin fluctuation contributing to the magnetoresistivity near the transition. Application of magnetic field along the c axis, renders a swift occurrence of CMR but only a slow tilting of the magnetic moments toward the c axis. The unparalleled changes indicate a non-consequential role of magnetic polarization.
Colossal magnetoresistance (CMR) and electroresistance (CER) induced by the electric field in spinel multiferroic CdCr2S4 are reported. It is found that a metal-insulator transition (MIT) in CdCr2S4 is triggered by the electrical field. In magnetic fields, the resistivity of CdCr2S4 responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr2S4 the unique compound to possess all four properties of the colossal magnetocapacitive (CMC), colossal electrocapacitive (CEC), CER, and CMR. The present results open a new venue for searching new materials to show CMR…
Colossal magnetoresistance is of great fundamental and technological significance and exists mostly in the manganites and a few other materials. Here we report colossal magnetoresistance that is starkly different from that in all other materials. The stoichiometric Mn3Si2Te6 is an insulator featuring a ferrimagnetic transition at 78 K. The resistivity drops by 7 orders of magnitude with an applied magnetic field above 9 Tesla, leading to an insulator-metal transition at up to 130 K. However, the colossal magnetoresistance occurs only when the magnetic field is applied along the magnetic hard a…
At low temperatures, EuTiO$_3$ system has very large resistivities and exhibits colossal magnetoresistance. Based on a first principle calculation and the dynamical mean-field theory for small polaron we have calculated the transport properties of EuTiO$_3$. It is found that due to electron-phonon interaction the conduction band may form a tiny subband which is close to the Fermi level. The tiny subband is responsible for the large resistivity. Besides, EuTiO$_3$ is a weak antiferromagnetic material and its magnetization would slightly shift the subband via exchange interaction between conduct…
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。
We report occurrence of large magnetoresistance in lightly doped antiferromagnetic paraelectric EuTiO3. Reports of magnetoresistance in rare-earth titanates (RTiO3 oxides) are very scarce because they are highly insulating at low temperatures. EuTiO3 is an insulator at 2.5 K and 1% La3+ substitution for Eu2+ lowers the resistivity over five orders of magnitude at 2.5 K. It is shown that Eu0.99La0.01TiO3 which is antiferromagnetic below T= 5.43 K shows large magnetoresistance over a wide temperature. At 2.5 K, magnetoresistance is -42 % for H = 6 kOe and it increases to -75 % for H = 7 T. Even …
We present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca$_3$Ru$_2$O$_7$. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattic…
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)
We review colossal magnetoresistance in single phase manganites, as related to the field sensitive spin charge interactions and phase separation; the rectifying property and negative/positive magnetoresistance in manganite/Nb:SrTiO3 pn junctions in relation to the special interface electronic structure; magnetoelectric coupling in manganite/ferroelectric structures that takes advantage of strain, carrier density, and magnetic field sensitivity; tunneling magnetoresistance in tunnel junctions with dielectric, ferroelectric, and organic semiconductor spacers using the fully spin polarized nature…
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。
We report the observation of a new phenomenon of colossal magnetoresistance in a 40 nm wide GaAs quantum well in the presence of an external magnetic field applied parallel to the high-mobility 2D electron layer. In a strong magnetic field, the magnetoresistance is observed to increase by a factor of ~300 from 0 to 45T without the system undergoing any metal-insulator transition. We discuss how this colossal magnetoresistance effect cannot be attributed to the spin degree-of-freedom or localization physics, but most likely emanates from strong magneto-orbital coupling between the two-dimension…
The coupling of magnetic and electronic degrees of freedom to the crystal lattice in the ferromagnetic semimetal EuB$_6$, which exhibits a complex ferromagnetic order and a colossal magnetoresistance (CMR) effect, %, very likely involving magnetic polarons, is studied by high-resolution thermal expansion and magnetostriction experiments. EuB$_6$ may be viewed as a model system, where pure magnetism-tuned transport and the response of the crystal lattice can be studied in a comparatively simple environment,i.e., not influenced by strong crystal-electric field effects and Jahn-Teller distortions…
We have recently reported a new mechanism of colossal magnetoresistance in electron doped Mn oxypnictides NdMnAsO1-xFx. Magnetoresistances of up to -95 percent at 3 K have been observed. Here we show that upon replacing Nd for Pr, the CMR is surprisingly no longer present. Instead a sizeable negative magnetoresistance is observed for PrMnAsO0.95F0.05 below 35 K (MR7T (12 K) = -13.4 percent for PrMnAsO0.9F0.05. A detailed neutron and synchrotron X-ray diffraction study of PrMnAsO0.95F0.05 has been performed, which shows that a structural transition, Ts, occurs at 35 K from tetragonal P4/nmm to …
Here we investigate antiferromagnetic Eu$_{5}$In$_{2}$Sb$_{6}$, a nonsymmorphic Zintl phase. Our electrical transport data show that Eu$_{5}$In$_{2}$Sb$_{6}$ is remarkably insulating and exhibits an exceptionally large negative magnetoresistance, which is consistent with the presence of magnetic polarons. From {\it ab initio} calculations, the paramagnetic state of Eu$_{5}$In$_{2}$Sb$_{6}$ is a topologically nontrivial semimetal within the generalized gradient approximation (GGA), whereas an insulating state with trivial topological indices is obtained using a modified Becke-Johnson potential.…
The n-type HgCr2Se4 exhibits a sharp semiconductor-to-metal transition (SMT) in resistivity accompanying the ferromagnetic order at TC = 106 K. Here, we investigate the effects of pressure and magnetic field on the concomitant SMT and ferromagnetic order by measuring resistivity, dc and ac magnetic susceptibility, as well as single-crystal neutron diffraction under various pressures up to 8 GPa and magnetic fields up to 8 T. Our results demonstrate that the ferromagnetic metallic ground state of n-type HgCr2Se4 is destabilized and gradually replaced by an antiferromagnetic, most likely a spira…
Within massive gravity, we construct a gravity dual for insulator/metal phase transition and colossal magnetoresistance (CMR) effect found in some manganese oxides materials. In heavy graviton limit, a remarkable magnetic-field-sensitive DC resistivity peak appears at the Curie temperature, where an insulator/metal phase transition happens and the magnetoresistance is scaled with the square of field-induced magnetization. We find that metallic and insulating phases coexist below the Curie point and the relation with the electronic phase separation is discussed.
EuB5.99C0.01 is a low-carrier density ferromagnet that is believed to be intrinsically inhomogeneous due to fluctuations of carbon content. In accordance with our previous studies, electric trasport of EuB5.99C0.01 close above temperature of the bulk ferromagnetic (FM) ordering is governed by magnetic polarons. Carbon-rich regions are incompatible with FM phase and therefore they act as spacers preventing magnetic polarons to link, to form FM clusters, and eventually to percolate and establish a (homogoneous) bulk FM state in this compound, what consequently causes additional (magneto)resistan…
We have grown La$_{1.37}$Sr$_{1.63}$Mn$_2$O$_7$ single crystals with a laser-diode-heated floating-zone furnace and studied the crystallinity, structure, and magnetoresistance (MR) effect by in-house X-ray Laue diffraction, X-ray powder diffraction, and resistance measurements. The La$_{1.37}$Sr$_{1.63}$Mn$_2$O$_7$ single crystal crystallizes into a tetragonal structure with space group \emph{I}4{/}\emph{mmm} at room temperature. At 0 T, the maximum resistance centers around $\sim$166.9 K. Below $\sim$35.8 K, it displays an insulating character with an increase in resistance upon cooling. An a…
The interfacial properties of Y0.6Pr0.4Ba2Cu3O7/La2/3Ca1/3MnO3 superlattices have been studied by resonant soft x-rays and diffuse scattered neutrons. Linearly polarized X-ray absorption at Cu L3 -edge reveals dramatic interfacial changes from the bulk including charge transfer between LCMO and YPBCO and an orbital reconstruction in the interface CuO2 plane. The similarities to the case of zero Pr-doping are due to the strongly hybridized covalent bond between Cu and Mn. However, reduced charge transfer and a more bulk-like interfacial orbital occupation are observed and related to the effect …
We explain the observed specific heat anomaly (and hence entropy change) in the colossal magnetoresistive manganite Sm0.55Sr0.45MnO3, by introducing phase separation into the current carrier density collapse theory via the notion of the ferromagnetic volume fraction. Within the same framework, we have also been able to explain the observed electrical resistivity of Sm0.55Sr0.45MnO3 by using appropriate expressions governing the scattering mechanisms far away from the transition. Fitting specific heat and resistivity results has allowed us to separate the hopping activation energy of polaronic …
Abnormal electronic properties of complex systems require new ideas concerning explanation of their behavior and possibility of realization. In this acticle we show that a colossal magnetoresistance is realized in the state of the topological Kondo insulator, that is similar to the Kondo insulator state in the Kondo lattice. The mechanism of the phenomenon is the following: in the spin gapless phase an external magnetic field induces the gap in the spectrum of spin excitations, the gap in the spectrum of fermions is opened due to a hybridization between spin and fermion subsystems at half fill…
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。
Colossal magnetoresistance (CMR) is a rare phenomenon in which the electronic resistivity of a material can be decreased by orders of magnitude upon application of a magnetic field. Such an effect could be the basis of the next generation of magnetic memory devices. Here we report CMR in the antiferromagnetic oxypnictide NdMnAsO1-xFx as a result of competition between an antiferromagnetic insulating phase with strong electron correlations and a paramagnetic semiconductor upon application of a magnetic field. The discovery of CMR in antiferromagnetic Mn2+ oxypnictide materials could open up an …
A bulk diluted magnetic semiconductor (Sr,K)(Zn,Mn)$_{2}$As$_{2}$ was synthesized with decoupled charge and spin doping. It has a hexagonal CaAl$_{2}$Si$_{2}$-type structure with the (Zn,Mn)$_{2}$As$_{2}$ layer forming a honeycomb-like network. Magnetization measurements show that the sample undergoes a ferromagnetic transition with a Curie temperature of 12 K and \revision{magnetic moment reaches about 1.5 $μ_{B}$/Mn under $μ_0H$ = 5 T and $T$ = 2 K}. Surprisingly, a colossal negative magnetoresistance, defined as $[ρ(H)-ρ(0)]/ρ(0)$, up to $-$38\% under a low field of $μ_0H$ = 0.1 T and to $-…
