Electronic transport in EuB6 (original) (raw)
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Magnetic, transport, and thermal properties of ferromagnetic EuB6
Journal of Applied Physics, 1979
Magnetic rneasuremcnts on Al-Ou" grown EuB 6 crystals show that this material orders ferromagnetically with a transition temperature Tc = 13.7 K. The effective moment derive<I rrom paramagnetic susceptibility measurements gives J.l.c« = 7.76 µ 8 , and the saturation magnetization extrapolated to 0 K is within 10% of the theoretical value of 7 µ 8 expected for Eu+ 2 • The magnetic order, however, cannot be that or a simple colinear ferromagnet because the magnetic specific heat in zero applied magnetic field shows a broad maximum centered about 9 K rather than the expected 1.-like a nomaly at 13.7 K. Finally, transport measuremen ts suggest that EuB 6 is an intrinsic semimental. •
Lattice Strain Accompanying the Colossal Magnetoresistance Effect in EuB6
Phys. Rev. Lett., 2014
The coupling of magnetic and electronic degrees of freedom to the crystal lattice in the ferromagnetic semimetal EuB6, which exhibits a complex ferromagnetic order and a colossal magnetoresistance (CMR) effect, is studied by high-resolution thermal expansion and magnetostriction experiments. EuB6 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 find a very large lattice response, quantified by (i) the magnetic Grüneisen parameter, (ii) the spontaneous strain when entering the ferromagnetic region and (iii) the magnetostriction in the paramagnetic temperature regime. Our analysis reveals that a significant part of the lattice effects originates in the magnetically-driven delocalization of charge carriers, consistent with the scenario of percolating magnetic polarons. A strong effect of the formation and dynamics of local magnetic clusters on the lattice parameters is suggested to be a general feature of CMR materials.
Concurrent magnetic and metal-insulator transitions in Eu[sub 1−x]Sm[sub x]B[sub 6] single crystals
Applied Physics Letters, 2009
The effects of magnetic doping on a EuB 6 single crystal were investigated based on magnetic and transport measurements. A modest 5% Sm substitution for Eu changes the magnetic and transport properties dramatically and gives rise to concurrent antiferromagnetic and metal-insulator transitions (MIT) from ferromagnetic MIT for EuB 6 . Magnetic doping simultaneously changes the itinerant carrier density and the magnetic interactions. We discuss the origin of the concurrent magnetic MIT in Eu 1-x Sm x B 6 . *corresponding author: mhjung@sogang.ac.kr 2 Electrons, the building blocks for condensed matter physics, have two fundamental physical quantities: charge and spin. The subtle interplay between these two quantities is not only useful for applications such as spintronics, but also presents an exciting challenge to understand how they are intertwined. One enchanting example is the search for magnetic polarons 1, 2 where charge carriers are accompanied by a local magnetic polarization and possibly distortions of a nearby crystal lattice. The percolation of MPs leads to concurrent ferromagnetic transition and MIT, showing that the magnetic and the transport properties are intrinsically entangled. In fact, MPs play an important role in the low-density region, where spatial fluctuations overwhelm thermal fluctuations. This interesting phenomenon has been proposed/observed in various contemporary condensed matter systems, such as high-Tc superconductors 3 , colossal magnetoresistance materials 4-6 , and diluted magnetic semiconductors 7 . Though various experiments indicate the existence of MPs 4, 5, 8 , it is still unclear how MPs evolve as the density of electrons (n e ) increases 9 . Thus, a systematic study for doping effects in a MP system is an interesting and challenging task.
Magnetic Semimetals and Quantized Anomalous Hall Effect in EuB 6
Exploration of the novel relationship between magnetic order and topological semimetals has received enormous interest in a wide range of both fundamental and applied research. Here we predict that "soft" ferromagnetic material EuB 6 can achieve multiple topological semimetal phases by simply tuning the direction of the magnetic moment. Explicitly, EuB 6 is a topological nodal-line semimetal when the moment is aligned along the [001] direction, and it evolves into a Weyl semimetal with three pairs of Weyl points by rotating the moment to the [111] direction. Interestingly, we identify a composite semimetal phase featuring the coexistence of a nodal line and Weyl points with the moment in the [110] direction. Topological surface states and anomalous Hall conductivity, which are sensitive to the magnetic order, have been computed and are expected to be experimentally observable. Large-Chern-number quantum anomalous Hall effect can be realized in its [111]-oriented quantum-well structures.
Journal of the Korean Physical Society, 2021
Temperature-dependent angle-resolved photoemission spectroscopy (ARPES) was carried out on single-crystalline EuB6 samples. By measuring ARPES spectra in an extended Brillouin zone, a B 2p hole pocket centered at the X point is clearly observed, thus proving the semimetallic nature of EuB6. Below the Curie temperature TC, ARPES spectra show two B 2p bands of which separation is due to an exchange interaction between local Eu 4f and itinerant B 2p electrons. The exchange splitting becomes smaller as the temperature increases and disappears well above TC. Additionally, a diffuse structure near the Fermi level survives just above TC. Such behavior is well described by Monte Carlo simulations of a Kondo lattice model, thus supporting the formation of magnetic polarons in EuB6, which accounts for the resistivity upturn near above TC when lowering the temperature.
Percolation and the Colossal Magnetoresistance of Eu-Based Hexaboride
Physical Review Letters, 2004
Upon substituting Ca for Eu in the local-moment ferromagnet EuB6, the Curie temperature TC decreases substantially with increasing dilution of the magnetic sublattice and is completely suppressed for x ≤ 0.3. The Ca substitution leads to significant changes of the electronic properties across the EuxCa1−xB6 series. Electron microscopy data for x ≈ 0.27 indicate a phase separation into Eu-and Ca-rich clusters of 5 to 10 nm diameter, leading to percolation-type phenomena in the electrical transport properties. The related critical concentration xp is approximately 0.3. For x ≈ 0.27, we observe colossal negative magnetoresistance effects at low temperatures, similar in magnitude as those reported for manganese oxides.
Magnetoresistance and thermoelectric transport in EuTi1-Nb O3
Solid State Communications, 2019
We report the impact of Nb substitution in EuTi 1-x Nb x O 3 (x = 0, 0.01, 0.03, 0.06 and 0.1) on the magnetization, resistivity, magnetoresistance (MR), thermopower (S) and thermal conductivity (κ) over a wide temperature range (T = 390-2.5 K). Partial replacement of Ti by Nb weakens the antiferromagnetic coupling between Eu-4f spins, drastically reduces low-temperature resistivity and induces insulator-metal transition above the Neel temperature. MR is negative and decreases from 20% for x = 0.01-0.5% for x = 0.1 at 2.5 K but the sign of MR changes to positive at higher temperatures for x = 0.06 and 0.1. The negative MR is suggested due to spindependent scattering of Ti-3d conduction electrons by localized Eu-4f spins and we fitted the experimental data to a theoretical model. The negative sign of S asserts electron doping. The values of S and κ systematically decrease with increasing Nb content. κ(T) is analyzed using the Debye-Callaway model.
Epitaxial growth, magnetoresistance, and electronic band structure of GdSb magnetic semimetal films
2022
Motivated by observations of extreme magnetoresistance (XMR) in bulk crystals of rare-earth monopnictide (RE-V) compounds and emerging applications in novel spintronic and plasmonic devices based on thin-film semimetals, we have investigated the electronic band structure and transport behavior of epitaxial GdSb thin films grown on III-V semiconductor surfaces. The Gd3+ ion in GdSb has a high spin S = 7/2 and no orbital angular momentum, serving as a model system for studying the effects of antiferromagnetic order and strong exchange coupling on the resulting Fermi surface and magnetotransport properties of RE-Vs. We present a surface and structural characterization study mapping the optimal synthesis window of thin epitaxial GdSb films grown on III-V lattice-matched buffer layers via molecular-beam epitaxy. To determine the factors limiting XMR in RE-V thin films and provide a benchmark for band-structure predictions of topological phases of RE-Vs, the electronic band structure of GdSb thin films is studied, comparing carrier densities extracted from magnetotransport, angle-resolved photoemission spectroscopy (ARPES), and density-functional theory (DFT) calculations. ARPES shows a hole-carrier rich, topologically trivial, semimetallic band structure close to complete electron-hole compensation, with quantum confinement effects in the thin films observed through the presence of quantumwell states. DFT-predicted Fermi wave vectors are in excellent agreement with values obtained from quantum oscillations observed in magnetic field-dependent resistivity measurements. An electron-rich Hall coefficient is measured despite the higher hole-carrier density, attributed to the higher electron Hall mobility. The carrier mobilities are limited by surface and interface scattering, resulting in lower magnetoresistance than that measured for bulk crystals.
Magnetism and spin transport in rare-earth-rich epitaxial terbium and europium iron garnet films
Rare-earth iron garnet thin films with perpendicular magnetic anisotropy (PMA) have recently attracted a great deal of attention for spintronic applications. Thulium iron garnet (TmIG) has been successfully grown and TmIG/Pt heterostructures have been characterized. However, TmIG is not the only rare-earth iron garnet that can be grown with PMA. We report the growth, magnetic, and spintronic properties of epitaxial terbium iron garnet (TbIG) and europium iron garnet (EuIG) thin films with PMA. Reciprocal space mapping shows the films are lattice matched to the substrate without strain relaxation, even for films up to 56 nm thick. The lattice strain and magnetostriction coefficient produce PMA in certain cases. TbIG grows on (111) gadolinium gallium garnet (GGG) with PMA due to the in-plane compressive strain, whereas TbIG on (111) substituted GGG (SGGG) is in tension and has an in-plane easy axis. EuIG grows with PMA on and GGG substrates, which facilitates the investigation of spintronic properties as a function of orientation. Both garnets have excess rare earth, which is believed to occupy Fe octahedral sites and in the case of TbIG is associated with an increase in the compensation temperature to 330 K, higher than the bulk value. Anomalous Hall effect (AHE) measurements of Pt/EuIG Hall crosses show that the spin mixing conductance of Pt/ (111) and (100) EuIG is similar. AHE measurements of Pt/TbIG Hall crosses reveal a sign change in the AHE amplitude at the compensation point analogous to all-metallic systems.