Ferromagnetic/metallic manganese perovskites, such as La2/3Sr1/3MnO3 (LSMO)are promising materials for the design and implementation of novel spintronic devices working at room temperature. However, their implementation in practical applications has been severely hampered due to the breakdown of their magnetotransport properties at temperatures well below their magnetic transition temperature. This breakdown has been usually associated to surface and interface related problems but its physical origin has not been clearly established yet. In this work we investigate the interface between La2/3Sr1/3MnO3 (LSMO) thin films and different capping layers by means of x-ray linear dichroism and transport measurements. Our data reveal that, irrespective to the capping material, LSMO/capping layer bilayers exhibit an antiferromegnetic/insulating phase at the interface, likely to originate from a preferential occupancy of Mn 3d 3z2-r2 eg orbitals. This phase, which extends ca. 2 unit cells, is also observed in an uncapped LSMO reference sample thus, pointing to an intrinsic interfacial phase separation phenomenon, likely to be promoted by the structural disruption and symmetry breaking at the LSMO free surface/interface. These experimental observations strongly suggest that the structural disruption at the LSMO interfaces play a major role on the observed depressed magnetotransport properties in manganite-based magnetic tunneling junctions and it is at the origin of the so-called dead layer.
Using first-principles calculations, we show that the (001) surface of the ferromagnet La$_{1-x}$Sr$_{x}$MnO$_{3}$ under epitaxial compression favors antiferromagnetic ordering in the first few surface layers, coexisting with ferromagnetic bulk order. The change in magnetic order is accompanied by a marked surface-related spectral pseudogap, signaling a metal-insulator near-transition at the surface. All surfaces exhibit huge outward relaxations an rumpling of the MnO$_{2}$ and LaO surface planes, causing a distinct shift in work function. The AF phase is an extreme surface-assisted case of th…
We investigate the possibility of controlling the magnetic phase transition of the heterointerface between a half-doped manganite La$_{0.5}$Ca$_{0.5}$MnO$_{3}$ and a multiferroic BiFeO$_{3}$ through magnetoelectric coupling. Using macroscopic magnetometry and element-selective x-ray magnetic circular dichroism at the Mn and Fe \emph{L}-edges, we discover that the ferroelectric polarization of BFO controls simultaneously the magnetization of BFO and LCMO. X-ray absorption spectra at oxygen \emph{K}-edge and linear dichroism at Mn \emph{L}-edge suggest that the interfacial coupling is mainly der…
To gain insights into the fundamental and characteristic features of the surface of doped manganites, we constructed a general magnetic phase diagram of La$_{1-x}$Sr$_{x}$MnO$_3$ (001) surfaces in the plane spanned by $x$ and the bulk tetragonal distortion $c/a$, from the first-principles calculations. We found that the surfaces are quite different from the bulk in the sense that both the (La, Sr)O and MnO$_2$ terminated surfaces show strong tendency toward antiferromagnetism (A-type and C-type respectively). The basic physics governing the phase diagram can be understood in terms of the surfa…
The origin of the resistivity minimum observed in strongly phase separated manganites has been investigated in single crystalline thin films of LPCMO (x~0.42, y~0.40). The antiferromagnetic/charge ordered insulator (AFM/COI)-ferromagnetic metal (FMM) phase transition, coupled with the colossal hysteresis between the field cool cooled and field cooled warming magnetization demonstrates strongly phase separated nature, which gives rise to non-equilibrium magnetic liquid state that freezes into a magnetic glass. The thermal cycling and magnetic field dependence of the resistivity unambiguously sh…
Charge-lattice fluctuations are observed in the layered perovskite manganite LaSr2Mn2O7 by Raman spectroscopy as high as 340 K and with decreasing temperature they become static and form a charge ordered (CO) phase below TCO=210 K. In the static regime, superlattice reflections are observed through neutron and x-ray diffraction with a propagation vector (h+1/4,k-1/4,l). Crystallographic analysis of the CO state demonstrates that the degree of charge and orbital ordering in this manganite is weaker than the charge ordering in three dimensional perovskite manganites. A TN=170K a type-A antiferro…
It is suggested that extrinsic inhomogeneities in mixed-valence manganites deserve more attention and they should be taking into account on equal footing with hypothetical phase separation while examinating experimental data and developing the theoretical models of influence of stoichiometric and other types of inhomogeneities on properties of these and other transition-metal oxides.
We present a detailed magnetic study of the Pr1/3Ca2/3MnO3 manganite, where we observe the presence of small ferromagnetic (FM) domains (diameter ~ 10A) immersed within the charge-ordered antiferromagnetic (AFM) host. Due to the interaction of the FM nanodroplets with a disordered AFM shell, the low-temperature magnetization loops present exchange bias (EB) under cooling in an applied magnetic field. Our analysis of the cooling field dependence of the EB yields an antiferromagnetic interface exchange coupling comparable to the bulk exchange constant of the AFM phase. We also observe training e…
Thin films of La0.7Sr0.3MnO3 on MgO show a metal insulator transition and colossal magnetoresistance. The shape of this transition can be explained by intrinsic spatial inhomogeneities, which give rise to a domain structure of conducting and insulating domains at the submicrometer scale. These domains then undergo a percolation transition. The tunneling conductance and tunneling gap measured by scanning tunneling spectroscopy were used to distinguish and visualize these domains.
We present evidence of direct electron tunneling across intrinsic insulating regions in sub-micrometer wide bridges of the phase separated ferromagnet (La,Pr,Ca)MnO$_3$. Upon cooling below the Curie temperature, a predominantly ferromagnetic supercooled state persists where tunneling across the intrinsic tunnel barriers (ITBs) results in metastable, temperature-independent, high-resistance plateaus over a large range of temperatures. Upon application of a magnetic field, our data reveal that the ITBs are extinguished resulting in sharp, colossal, low-field resistance drops. Our results compare…
Conductive and electrostatic atomic force microscopy (cAFM and EFM) are used to investigate the electric conduction at nominally neutral domain walls in hexagonal manganites. The EFM measurements reveal a propensity of mobile charge carriers to accumulate at the nominally neutral domain walls in ErMnO3, which is corroborated by cAFM scans showing locally enhanced d.c. conductance. Our findings are explained based on established segregation enthalpy profiles for oxygen vacancies and interstitials, providing a microscopic model for previous, seemingly disconnected observations ranging from insul…
Transmission of information using the spin of the electron as well as its charge requires a high degree of spin polarization at surfaces. At surfaces however this degree of polarization can be quenched by competing interactions. Using a combination of surface sensitive x-ray and tunneling probes, we show for the quasi-two-dimensional bilayer manganites that the outermost Mn-O bilayer, alone, is affected: it is a 1-nm thick insulator that exhibits no long-range ferromagnetic order while the next bilayer displays the full spin polarization of the bulk. Such an abrupt localization of the surface …
Phase diagrams in the plane of $r_A$ (the average ionic radius, related to one-electron bandwidth $W$) and $σ^2$ (the ionic radius variance, measuring the quenched disorder), or ``bandwidth-disorder phase diagrams'', have been established for perovskite manganites, with three-dimensional (3$D$) Mn-O network. Here we establish the intrinsic bandwidth-disorder phase diagram of half-doped layered manganites with the two-dimensional (2$D$) Mn-O network, examining in detail the ``mother state'' of the colossal magnetoresistance (CMR) phenomenon in crystals without ferromagnetic instability. The con…
By directly measuring electrical hysteresis loops using the Positive-Up Negative-Down (PUND) method, we accurately determined the remanent ferroelectric polarization Pr of orthorhombic RMnO3 (R = Ho, Tm, Yb, and Lu) compounds below their E-type spin ordering temperatures. We found that LuMnO3 has the largest Pr of 0.17 uC/cm^2 at 6 K in the series, indicating that its single-crystal form can produce a Pr of at least 0.6 \muuC/cm^2 at 0 K. Furthermore, at a fixed temperature, Pr decreases systematically with increasing rare earth ion radius from R = Lu to Ho, exhibiting a strong correlation wit…
Intrinsic antiferromagnetism in van der Waals (vdW) monolayer (ML) crystals enriches the understanding regarding two-dimensional (2D) magnetic orders and holds special virtues over ferromagnetism in spintronic applications. However, the studies on intrinsic antiferromagnetism are sparse, owing to the lack of net magnetisation. In this study, by combining spin-polarised scanning tunnelling microscopy and first-principles calculations, we investigate the magnetism of vdW ML CrTe2, which has been successfully grown through molecular beam epitaxy. Surprisingly, we observe a stable antiferromagneti…
We have measured the electrical resistance of micrometric to nanometric powders of the La$_{5/8-y}$Pr$_y$Ca$_{3/8}$MnO$_3$ (LPCMO with y=0.3) manganite for hydrostatic pressures up to 4 kbar. By applying different final thermal treatments to samples synthesized by a microwave assisted denitration process, we obtained two particular grain characteristic dimensions (40 nm and 1000 nm) which allowed us to analyze the grain size sensitivity of the electrical conduction properties of both the metal electrode interface with manganite (Pt / LPCMO) as well as the intrinsic intergranular interfaces for…
We report a detailed study of step-like metamagnetic transitions in the magnetization and resistivity of polycrystalline Pr0.5Ca0.5Mn0.95Co0.05O3. The steps have a sudden onset below a critical temperature, are extremely sharp (width < 0.2 mT), and occur at critical fields which are linearly dependent on the absolute value of the cooling field in which the sample is prepared. Similar transitions are also observed at low temperature in non-Co doped manganites, including single crystal samples. These data show that the steps are an intrinsic property, qualitatively different from either previous…
The oxygen stoichiometry has a large influence on the physical and chemical properties of complex oxides. Most of the functionality in e.g. catalysis and electrochemistry depends in particular on control of the oxygen stoichiometry. In order to understand the fundamental properties of intrinsic surfaces of oxygen-deficient complex oxides, we report on in situ temperature dependent scanning tunnelling spectroscopy experiments on pristine oxygen deficient, epitaxial manganite films. Although these films are insulating in subsequent ex situ in-plane electronic transport experiments at all tempera…
The control of magnetization via the application of an electric field, known as magnetoelectric coupling, is among the most fascinating and active research areas today. In addition to fundamental scientific interest, magnetoelectric effects may lead to new device concepts for data storage and processing. There are several known mechanisms for magnetoelectric coupling that include intrinsic effects in single-phase materials, strain induced coupling in two-phase composites, and electronically-driven effects at interfaces. Here we explore a different type of magnetoelectric effect at a ferromagne…
We have studied the effect of irreversibility induced by repeated thermal cycles on the electric transport and magnetization of polycrystalline samples of La0.5Ca0.5MnO3 and La0.325Pr0.3Ca0.375MnO3. An increase of the resistivity and a decrease of the magnetization at different temperature ranges after cycling is obtained in the temperature range between 300 K and 30 K. Both compounds are known to exhibit intrinsic submicrometric coexistence of phases and undergo a sequence of phase transitions related to structural changes. Changes induced by thermal cycling can be partially inhibited by appl…
Intrinsic triferroicity is essential and highly sought for novel device applications, such as high-density multistate data storage. So far, the intrinsic triferroicity has only been discussed in three-dimensional systems. Herein on basis of first-principles, we report the intrinsic triferroicity in two-dimensional lattice. Being exfoliatable from the layered bulk, single-layer FeO2H is shown to be an intrinsically triferroic semiconductor, presenting antiferromagnetism, ferroelasticity and ferroelectricity simultaneously. Moreover, the directional control of its ferroelectric polarization is a…
In this study we report the effect of sintering temperature on the low field magnetotransport properties of La_0.7Ca_0.3Mn_O3 manganite synthesized through polymeric precursor route. The La_0.7Ca_0.3MnO_3 has been sintered at 600^oC (S6), 700^oC (S7), 800^oC (S8), 900^oC (S9) and 1000^oC (S10). XRD confirms that phase formation starts at 600^oC. All the samples are single phasic having orthorhombic unit cell. The lattice parameters decrease on lowering the sintering temperature (T_S). The crystallite as well as particle size also show strong dependence on the sintering temperature. All the sam…
One-dimensional (1D) confinement has been revealed to effectively tune the properties of materials in homogeneous states. The 1D physics can be further enriched by electronic inhomogeneity, which unfortunately remains largely unknown. Here we demonstrate the ultra-high sensitivity to magnetic fluctuations and the tunability of phase stability in the electronic transport properties of self-assembled electronically phase-separated manganite nanowires with extreme aspect ratio. The onset of magnetic nano-droplet state, a precursor to the ferromagnetic metallic state, is unambiguously revealed, wh…
In most conductors current flow perpendicular to electric field direction (Hall current) can be explained in terms of the Lorentz forces present when charged particles flow in an external magnetic field. However, as established in the very early work of Edwin Hall, ferromagnetic conductors such as Fe, Co, and Ni have an anomalous Hall conductivity contribution that cannot be attributed to Lorentz forces and therefore survives in the absence of a magnetic field. Although the anomalous Hall effect is experimentally strong, it has stood alone among metallic transport effects for much of the last …
The rare-earth ions (RE = Eu, Dy Ho, Tm, Y) substituted charge-ordered antiferromagnetic manganites, Pr0.45RE0.05Ca0.5MnO3, were studied for the magnetic and the transport properties in the presence of external magnetic-fields of up to 14 Tesla. Regardless of the intrinsic magnetic property of RE ions, all the compounds exhibit successive step-like metamagnetic transitions at low temperatures, which are strongly correlated to their electronic transitions. At any fixed temperature in two different temperature-regimes, we observed contrary effects of the magnetic-field cycling on the resistivity…
Strong correlated manganites are still under intense research owing to their complex phase diagrams in terms of the Sr-doping and their sensitivity to intrinsic and extrinsic structural deformations. Here, we performed x-ray absorption spectroscopy measurements of manganites bilayers to explore the effects that a local Sr-doping gradient produce on the charge and antiferromagnetic anisotropies. In order to gradually tune the Sr-doping level along the axis perpendicular to the samples we have grown a series of bilayers with different thicknesses of low-doped manganites (from 0 nm to 6 nm) depos…
Stoichiometry-Controlled Structural Order and Tunable Antiferromagnetism in $\mathrm{Fe}_{x}\mathrm{NbSe_2}$ ($0.05 \le x \le 0.38$)
Tsung-Dao Lee Institute, School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院李政道研究所）；Shenzhen Institute for Quantum Science and Engineering, Southern University of Science and Technology（南方科技大学量子科学与工程研究院）；International Quantum Academy（国际量子科学院）；Zhangjiang Institute for Advanced Study, Shanghai Jiao Tong University（上海交通大学张江高等研究院）；State Key Laboratory of Micro-nano Engineering Science, Shanghai Jiao Tong University（上海交通大学微纳制造技术国家重点实验室）
A macroscopic phase separation, in which ferromagnetic clusters are observed in an insulating matrix, is sometimes observed, and believed to be essential to the colossal magnetoresistive (CMR) properties of manganese oxides. The application of a magnetic field may indeed trigger large magnetoresistance effects due to the percolation between clusters allowing the movement of the charge carriers. However, this macroscopic phase separation is mainly related to extrinsic defects or impurities, which hinder the long-ranged charge-orbital order of the system. We show in the present article that rath…
Coexistence of Superconductivity and Antiferromagnetism in Topological Magnet MnBi2Te4 Films
The Pennsylvania State University（宾夕法尼亚州立大学）；Paul Scherrer Institute（保罗谢尔研究所）；National Institute of Standards and Technology（美国国家标准与技术研究院）；National High Magnetic Field Laboratory（国家高磁场实验室）
Field-tunable partial antiferromagnetism, glassy spin dynamics, and magnetodielectric coupling in the quasi-one-dimensional spin-chain compound Ca3CoIrO6
Interplay of Intersite Charge Transfer, Antiferromagnetism, and Strain in Barocaloric ACu$_3$Fe$_4$O$_{12}$ Quadruple Perovskites
Centro de Investigación en Ciencia e Ingeniería de Materiales, Universidad de Costa Rica（哥斯达黎加大学材料科学与工程研究中心）；Escuela de Física, Universidad de Costa Rica（哥斯达黎加大学物理学院）
Intrinsic Even-Odd Thickness-Driven Anomalous Hall in Epitaxial MnBi2Te4 Thin Films
Oak Ridge National Laboratory（橡树岭国家实验室）；Pennsylvania State University（宾夕法尼亚州立大学）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；Argonne National Laboratory（阿贡国家实验室）；University of Pennsylvania（宾夕法尼亚大学）
With x-ray absorption spectroscopy we investigated the orbital reconstruction and the induced ferromagnetic moment of the interfacial Cu atoms in YBa$_2$Cu$_3$O$_{7}$/La$_{2/3}$Ca$_{1/3}$MnO$_3$ (YBCO/LCMO) and La$_{2-x}$Sr$_{x}$CuO$_4$/La$_{2/3}$Ca$_{1/3}$MnO$_3$ (LSCO/LCMO) multilayers. We demonstrate that these electronic and magnetic proximity effects are coupled and are common to these cuprate/manganite multilayers. Moreover, we show that they are closely linked to a specific interface termination with a direct Cu-O-Mn bond. We furthermore show that the intrinsic hole doping of the cuprat…
The possibility of controlling the interfacial properties of artificial oxide heterostructures is still attracting researchers in the field of materials engineering. Here, we used surface sensitive techniques and high-resolution transmission electron microscopy to investigate the evolution of the surface spin-polarization and lattice strains across the interfaces between La0.66Sr0.33MnO3 thin films and low-doped manganites as capping layers. We have been able to finely tune the interfacial spin-polarization by changing the capping layer thickness and composition. The spin-polarization was foun…
The influence of an external static magnetic field (up to 480 mT)on the structural properties of EuTiO$_3$ (ETO) polycrystalline samples was examined by powder XRD at the Elettra synchrotron facilities in the temperature range 100-300K. While the cubic to tetragonal structural phase transition temperature in this magnetic field range remains almost unaffected, significant lattice effects appear at two characteristic temperatures (~200K and 250K), which becomes more pronounced at a critical threshold magnetic field. At ~200K a change in the sign of the magnetostriction is detected attributed to…
The electronic structure of the interface between Tris (8-hydroxyquinolino)-aluminum (Alq3) and La0.7Sr0.3MnO3 manganite (LSMO) was investigated by means of photoelectron spectroscopy. As demonstrated recently this interface is characterized by efficient spin injection in organic spintronic devices. We detected a strong interface dipole of about 0.9 eV that shifts down the whole energy diagram of the Alq3 with respect to the vacuum level. This modifies the height of the barriers for the holes injection to 1.7 eV, indicating that hole injection from LSMO into Alq3 is more difficult than it was …
The exploration of magnetism in two-dimensional layered materials has attracted extensive research interest. For the monoclinic phase CrI3 with interlayer antiferromagnetism, finding a static and robust way of realizing the intrinsic interlayer ferromagnetic coupling is desirable. In this Letter, we study the electronic structure and magnetic properties of the nonmagnetic element (e.g., O, S, Se, N, P, As and C) doped bi- and triple-layer CrI3 systems via first-principles calculations. Our results demonstrate that O, P, S, As, and Se doped CrI3 bilayer can realize interlayer ferromagnetism. Fu…
Electronic structure of the three-dimensional colossal magnetoresistive perovskite La1-xSrxMnO3 has been established using soft-X-ray ARPES with its intrinsically sharp definition of three-dimensional electron momentum. The experimental results show much weaker polaronic coupling compared to the bilayer manganites and are consistent with the GGA+U band structure. The experimental Fermi surface unveils the canonical topology of alternating three-dimensional electron spheres and hole cubes, with their shadow contours manifesting the rhombohedral lattice distortion. This picture has been confirme…
We employed a scanning tunneling microscope to image the (001) surface topography and local density of states (LDOS) in La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ (x=0.32, LSMO) single crystals below the Curie temperature (T$_C$ = 120 K). The LDOS maps revealed a stripe-like modulation propagating along the tetragonal a axis with a wavelength of about 1.6 Å, which is indicative of a charge density wave (CDW). The observed CDW in the x=0.32 sample is far from the Fermi surface nesting instability as compared with the data of angle resolved photoemission spectroscopy in an x=0.40 sample. The stripe model…
