R-3 Repository :: Browsing by Author "Morosan, E."

Browsing by Author "Morosan, E."

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An itinerant antiferromagnetic metal without magnetic constituents
(Nature Publishing Group, 2015) Svanidze, E.; Wang, Jiakui K.; Besara, T.; Liu, L.; Huang, Q.; Siegrist, T.; Frandsen, B.; Lynn, J.W.; Nevidomskyy, Andriy H.; Gamża, Monika B.; Aronson, M.C.; Uemura, Y.J.; Morosan, E.
The origin of magnetism in metals has been traditionally discussed in two diametrically opposite limits: itinerant and local moments. Surprisingly, there are very few known examples of materials that are close to the itinerant limit, and their properties are not universally understood. In the case of the two such examples discovered several decades ago, the itinerant ferromagnets ZrZn2 and Sc3In, the understanding of their magnetic ground states draws on the existence of 3d electrons subject to strong spin fluctuations. Similarly, in Cr, an elemental itinerant antiferromagnet with a spin density wave ground state, its 3d electron character has been deemed crucial to it being magnetic. Here, we report evidence for an itinerant antiferromagnetic metal with no magnetic constituents: TiAu. Antiferromagnetic order occurs below a Néel temperature of 36 K, about an order of magnitude smaller than in Cr, rendering the spin fluctuations in TiAu more important at low temperatures. This itinerant antiferromagnet challenges the currently limited understanding of weak itinerant antiferromagnetism, while providing insights into the effects of spin fluctuations in itinerant–electron systems.
Anomalous Metamagnetism in the Low Carrier Density Kondo Lattice YbRh3Si7
(American Physical Society, 2018) Rai, Binod K.; Chikara, S.; Ding, Xiaxin; Oswald, Iain W.H.; Schönemann, R.; Loganathan, V.; Hallas, A.M.; Cao, H.B.; Stavinoha, Macy; Chen, T.; Man, Haoran; Carr, Scott; Singleton, John; Zapf, Vivien; Benavides, Katherine A.; Chan, Julia Y.; Zhang, Q.R.; Rhodes, D.; Chiu, Y.C.; Balicas, Luis; Aczel, A.A.; Huang, Q.; Lynn, Jeffrey W.; Gaudet, J.; Sokolov, D.A.; Walker, H.C.; Adroja, D.T.; Dai, Pengcheng; Nevidomskyy, Andriy H.; Huang, C.-L.; Morosan, E.
We report complex metamagnetic transitions in single crystals of the new low carrier Kondo antiferromagnet YbRh3Si7. Electrical transport, magnetization, and specific heat measurements reveal antiferromagnetic order at TN=7.5 K. Neutron diffraction measurements show that the magnetic ground state of YbRh3Si7 is a collinear antiferromagnet, where the moments are aligned in the ab plane. With such an ordered state, no metamagnetic transitions are expected when a magnetic field is applied along the c axis. It is therefore surprising that high-field magnetization, torque, and resistivity measurements with H∥c reveal two metamagnetic transitions at μ0H1=6.7 T and μ0H2=21 T. When the field is tilted away from the c axis, towards the ab plane, both metamagnetic transitions are shifted to higher fields. The first metamagnetic transition leads to an abrupt increase in the electrical resistivity, while the second transition is accompanied by a dramatic reduction in the electrical resistivity. Thus, the magnetic and electronic degrees of freedom in YbRh3Si7 are strongly coupled. We discuss the origin of the anomalous metamagnetism and conclude that it is related to competition between crystal electric-field anisotropy and anisotropic exchange interactions.
Band Jahn-Teller structural phase transition inﾠY2In
(American Physical Society, 2018) Svanidze, E.; Georgen, C.; Hallas, A.M.; Huang, Q.; Santiago, J.M.; Lynn, J.W.; Morosan, E.
The number of paramagnetic materials that undergo a structural phase transition is rather small, which can perhaps explain the limited understanding of the band Jahn-Teller mechanism responsible for this effect. Here we present a structural phase transition observed in paramagnetic Y2In at temperature T0=250±5 K. Below T0, the high-temperature hexagonal P63/mmc phase transforms into the low-temperature orthorhombic Pnma phase. This transition is accompanied by an unambiguous thermal hysteresis of about 10 K, observed in both magnetic susceptibility M/H(T) and resistivity ρ(T), indicating a first-order transition. Band structure calculations suggest a band Jahn-Teller mechanism, during which the degeneracy of electron bands close to the Fermi energy is broken. We establish that this structural phase transition does not have a magnetic component; however, the possibility of a charge density wave formation has not been eliminated.
CeIr3Ge7: A local moment antiferromagnetic metal with extremely low ordering temperature
(American Physical Society, 2018) Rai, Binod K.; Banda, Jacintha; Stavinoha, Macy; Borth, R.; Jang, D.-J.; Benavides, Katherine A.; Sokolov, D. A.; Chan, Julia Y.; Nicklas, M.; Brando, Manuel; Huang, C.-L.; Morosan, E.
CeIr3Ge7 is an antiferromagnetic metal with a remarkably low ordering temperature TN=0.63K, while most Ce-based magnets order between 2 and 15 K. Thermodynamic and transport properties as a function of magnetic field or pressure do not show signatures of Kondo correlations, interaction competition, or frustration, as had been observed in a few antiferromagnets with comparably low or lower TN. The averaged Weiss temperature measured below 10 K is comparable to TN, suggesting that the Ruderman-Kittel-Kasuya-Yosida exchange coupling is very weak in this material. The unusually low TN in CeIr3Ge7 can therefore be attributed to the large Ce-Ce bond length of about 5.7 Å, which is about 1.5 Å larger than in the most Ce-based intermetallic systems.
Charge-neutral fermions and magnetic field-driven instability in insulating YbIr3Si7
(Springer Nature, 2022) Sato, Y.; Suetsugu, S.; Tominaga, T.; Kasahara, Y.; Kasahara, S.; Kobayashi, T.; Kitagawa, S.; Ishida, K.; Peters, R.; Shibauchi, T.; Nevidomskyy, A. H.; Qian, L.; Morosan, E.; Matsuda, Y.
Kondo lattice materials, where localized magnetic moments couple to itinerant electrons, provide a very rich backdrop for strong electron correlations. They are known to realize many exotic phenomena, with a dramatic example being recent observations of quantum oscillations and metallic thermal conduction in insulators, implying the emergence of enigmatic charge-neutral fermions. Here, we show that thermal conductivity and specific heat measurements in insulating YbIr3Si7 reveal emergent neutral excitations, whose properties are sensitively changed by a field-driven transition between two antiferromagnetic phases. In the low-field phase, a significant violation of the Wiedemann-Franz law demonstrates that YbIr3Si7 is a charge insulator but a thermal metal. In the high-field phase, thermal conductivity exhibits a sharp drop below 300 mK, indicating a transition from a thermal metal into an insulator/semimetal driven by the magnetic transition. These results suggest that spin degrees of freedom directly couple to the neutral fermions, whose emergent Fermi surface undergoes a field-driven instability at low temperatures.
Chemical tuning of electrical transport in Ti1−xPtxSe2−y
(American Physical Society, 2015) Chen, Justin S.; Wang, Jiakui K.; Carr, Scott V.; Vogel, Sven C.; Gourdon, Olivier; Dai, Pengcheng; Morosan, E.
The structural and transport properties of polycrystalline Ti1−xPtxSe2−y(x≤0.13,y≤0.2) are studied, revealing highly tunable electrical properties, spanning nearly ten orders of magnitude in scaled resistivity. Using x-ray and neutron diffraction, Pt is found to dope on the Ti site. In the absence of Pt doping (for x=0), Se deficiency (y>0) increases the metallic character of TiSe2, while a large increase of the low-temperature resistivity is favored by a lack of Se deficiency (y=0) and increasing amounts of doped Pt (x>0). The chemical tuning of the resistivity in Ti1−xPtxSe2−y with Se deficiency and Pt doping results in a metal-to-insulator transition. Simultaneous Pt doping and Se deficiency (x,y>0) confirms the competition between the two opposing trends in electrical transport, with the main outcome being the suppression of the charge density wave transition below 2 K for y=2x=0.18. Band structure calculations on a subset of Ti1−xPtxSe2−y compositions are in line with the experimental observations.
Cluster-glass behavior induced by local moment doping in the itinerant ferromagnet Sc3.1In
(American Physical Society, 2013) Svanidze, E.; Morosan, E.
In the presented work, Sc3.1In, a weak itinerant ferromagnet with no magnetic constituents, is doped with Er3+ local moment ions, to form (Sc1−xErx )3.1In. As x increases, theWeiss-like temperature θ stays positive and nearly triples up to x = 0.10. Moreover, Er doping of as little as x = 0.02 induces a cluster-glass state, which persists up to x = 0.10, as evidenced by dc and ac susceptibility measurements, and confirmed by the Vogel-Fulcher Analysis.
Competing charge and magnetic order in the candidate centrosymmetric skyrmion host ${\mathrm{EuGa}}_{2}{\mathrm{Al}}_{2}$
(American Physical Society, 2023) Vibhakar, A. M.; Khalyavin, D. D.; Moya, J. M.; Manuel, P.; Orlandi, F.; Lei, S.; Morosan, E.; Bombardi, A.
Eu(Ga1−xAlx)4 are centrosymmetric systems that have recently been identified as candidates to stabilize topologically nontrivial magnetic phases, such as skyrmion lattices. In this Letter, we present a high-resolution resonant x-ray and neutron scattering study on EuGa2Al2 that provides new details of the complex coupling between the electronic ordering phenomena. Our results unambiguously demonstrate that the system orders to form a spin density wave with moments aligned perpendicular to the direction of the propagation vector below 19.5 K, and upon further cooling below 15 K, a cycloid with moments in the ab plane, in contrast to what has been reported in the literature. We show that concomitant with the onset of the spin density wave is the suppression of the charge density wave order, indicative of a coupling between the localized 4f electrons and itinerant electron density. Furthermore, we demonstrate that the charge density wave order breaks the fourfold symmetry present in the I4/mmm crystal structure, thus declassifying these systems as square-net magnets.
Correlations of crystallographic defects and anisotropy with magnetotransport properties in FexTaS2 single crystals (0.23≤x≤0.35)
(American Physical Society, 2016) Chen, Chih-Wei; Chikara, Shalinee; Zapf, Vivien S.; Morosan, E.
Very large magnetoresistance discovered in single crystals of the ferromagnetic Fe-intercalated transition-metal dichalcogenide Fe0.28TaS2 was attributed to the deviation of the Fe concentration from commensurate values (x=1/4 or 1/3), which caused magnetic moment misalignments. Here we report a study of FexTaS2 crystals with 0.23≤x≤0.35, demonstrating that crystallographic defects lead to spin disorder, which correlates with magnetotransport properties, such as switching magnetic field HS, magnetoresistance (MR), and even zero-field resistivity ρ0 and temperature coefficient A in ρ(T)=ρ0+AT2: The ordering temperature TC and Weiss temperature θW are maximized at the superstructure composition x=1/4, whereas Hs, MR, ρ0, and A are minimum. Conversely, at a composition intermediate between the superstructure compositions x=1/4 and 1/3, the corresponding magnetotransport properties reach local maxima.
Crystalline electric field of Ce in trigonal symmetry: CeIr3Ge7 as a model case
(American Physical Society, 2018) Banda, J.; Rai, B.K.; Rosner, H.; Morosan, E.; Geibel, C.; Brando, M.
The crystalline electric field (CEF) of Ce3+ in trigonal symmetry has recently become of some relevance, for instance, in the search of frustrated magnetic systems. Fortunately, it is one of the CEF cases in which a manageable analytic solution can be obtained. Here, we present this solution for the general case, and use this result to determine the CEF scheme of the new compound CeIr3Ge7 with the help of T-dependent susceptibility and isothermal magnetization measurements. The resulting CEF parameters B02=34.4K, B04=0.82K, and B34=67.3K correspond to an exceptionally large CEF splitting of the first and second excited levels, 374 K and 1398 K, and a large mixing between the ∣∣±52⟩ and the ∣∣∓12⟩ states. This indicates a very strong easy plane anisotropy with an unusually small c-axis moment. Using the same general expressions, we show that the properties of the recently reported system CeCd3As3 can also be described by a similar CEF scheme, providing a much simpler explanation for its magnetic properties than the initial proposal. Moreover, a similar strong easy plane anisotropy has also been reported for the two compounds CeAuSn and CePdAl4Ge2, indicating that the CEF scheme elaborated here for CeIr3Ge7 corresponds to an exemplary case for Ce3+ in trigonal symmetry.
High hardness in the biocompatible intermetallic compound β-Ti3Au
(AAAS, 2016) Svanidze, Eteri; Besara, Tiglet; Ozaydin, M. Fevsi; Tiwary, Chandra Sekhar; Wang, Jiakui K.; Radhakrishnan, Sruthi; Mani, Sendurai; Xin, Yan; Han, Ke; Liang, Hong; Siegrist, Theo; Ajayan, Pulickel M.; Morosan, E.
The search for new hard materials is often challenging, but strongly motivated by the vast application potential such materials hold. Ti3Au exhibits high hardness values (about four times those of pure Ti and most steel alloys), reduced coefficient of friction and wear rates, and biocompatibility, all of which are optimal traits for orthopedic, dental, and prosthetic applications. In addition, the ability of this compound to adhere to ceramic parts can reduce both the weight and the cost of medical components. The fourfold increase in the hardness of Ti3Au compared to other Ti–Au alloys and compounds can be attributed to the elevated valence electron density, the reduced bond length, and the pseudogap formation. Understanding the origin of hardness in this intermetallic compound provides an avenue toward designing superior biocompatible, hard materials.
Intermediate valence in single crystals of (Lu1−x Y b x )3Rh4Ge13 (0 ≤ x ≤ 1)
(AIP Publishing LLC, 2015) Rai, Binod K.; Morosan, E.
Single crystals of (Lu1−x Y b x )3Rh4 Ge 13 were characterized by magnetization, specific heat, and electrical resistivity measurements. Doping Yb into the non-magnetic Lu3Rh4 Ge 13 compound tunes this cubic system’s properties from a superconductor with disordered metal normal state (x < 0.05) to a Kondo for 0.05 ≤ x ≤0.2 and intermediate valence at the highest Yb concentrations. The evidence for intermediate Yb valence comes from a broad maximum in the magnetic susceptibility and X-ray photoelectron spectroscopy. Furthermore, the resistivity displays a local maximum at finite temperatures at intermediate compositions x, followed by apparent metallic behavior closest to the Yb end compound in the series.
Intermediate valence to heavy fermion through a quantum phase transition in Yb3(Rh1−xTx)4Ge13 (T=Co,Ir) single crystals
(American Physical Society, 2016) Rai, Binod K.; Oswald, Iain W.H.; Chan, Julia Y.; Morosan, E.
Single crystals of Yb3(Rh1−xTx)4Ge13 (T=Co,Ir) have been grown using the self-flux method. Powder x-ray diffraction data on these compounds are consistent with the cubic structure with space group Pm3¯n. Intermediate-valence behavior is observed in Yb3(Rh1−xTx)4Ge13 upon T = Co doping, while T = Ir doping drives the system into a heavy-fermion state. Antiferromagnetic order is observed in the Ir-doped samples Yb3(Rh1−xTx)4Ge13 for 0.5
Low-carrier density and fragile magnetism in a Kondo lattice system
(American Physical Society, 2019) Rai, Binod K.; Oswald, Iain W.H.; Ban, Wenjing; Huang, C.-L.; Loganathan, V.; Hallas, A.M.; Wilson, M.N.; Luke, G.M.; Harriger, L.; Huang, Q.; Li, Y.; Dzsaber, Sami; Chan, Julia Y.; Wang, N.L.; Paschen, Silke; Lynn, J.W.; Nevidomskyy, Andriy H.; Dai, Pengcheng; Si, Q.; Morosan, E.; Rice Center for Quantum Materials
Kondo-based semimetals and semiconductors are of extensive current interest as a viable platform for strongly correlated states in the dilute carrier limit. It is thus important to explore the routes to understand such systems. One established pathway is through the Kondo effect in metallic nonmagnetic analogs, in the so called half-filling case of one conduction electron and oneﾠ4fﾠelectron per site. Here, we demonstrate that Kondo-based semimetals develop out of conduction electrons with a low-carrier density in the presence of an even number of rare-earth sites. We do so by studying the Kondo materialﾠYb3Ir4Ge13ﾠalong with its closed-4f-shell counterpart,ﾠLu3Ir4Ge13. Through magnetotransport, optical conductivity, and thermodynamic measurements, we establish that the correlated semimetallic state ofﾠYb3Ir4Ge13ﾠbelow its Kondo temperature originates from the Kondo effect of a low-carrier conduction-electron background. In addition, it displays fragile magnetism at very low temperatures, which in turn, can be tuned to a Griffiths-phase-like regime through Lu-for-Yb substitution. These findings are connected with recent theoretical studies in simplified models. Our results can pave the way to exploring strong correlation physics in a semimetallic environment.
Magnetic and transport properties of the layered transition-metal pnictides R3T4As4O2−δ (R = La, Ce, Pr, Nd, and Sm, T = Ni, Cu)
(American Physical Society, 2014) Wang, Jiakui K.; Marcinkova, A.; Chen, Chih-Wei; He, Hua; Aronson, Meigan; Morosan, E.
The magnetic and transport properties of the novel R3T 4As4O2−δ (R = La, Ce, Pr, Nd and Sm, T = Ni and Cu) layered materials were studied using structural and physical properties measurements. Varying the rare-earth ion led to the observation of diverse physical properties including superconductivity for R = La and T = Ni, ferromagnetic or antiferromagnetic order for R = Ce, Pr, and Sm, or spin-glass behavior in Nd3Ni4As4O2−δ. These complex magnetic and electronic properties are discussed in light of the crystalline anisotropy in these layered compounds.
Modulated magnetism and anomalous electronic transport in Ce3Cu4As4O2
(American Physical Society, 2016) Wang, Jiakui K.; Wu, Shan; Qiu, Yiming; Rodriguez-Rivera, Jose A.; Huang, Qingzhen; Broholm, C.; Morosan, E.
The complex magnetism and transport properties of tetragonal Ce3Cu4As4O2 were examined through neutron scattering and physical property measurements on polycrystalline samples. The lamellar structure consists of alternating layers of CeCu4As4 with a single square Ce lattice and Ce2O2 bilayers. Peaks in the specific heat at the Néel temperature TN=24 K, T2=16 K, and T3=1.9 K indicate three magnetic phase transitions or distinct crossover phenomena. For T
Non-Fermi Liquid Behavior Close to a Quantum Critical Point in a Ferromagnetic State without Local Moments
(American Physical Society, 2015) Svanidze, E.; Liu, L.; Frandsen, B.; White, B.D.; Besara, T.; Goko, T.; Medina, T.; Munsie, T.J.S.; Luke, G.M.; Zheng, D.; Jin, C.Q.; Siegrist, T.; Maple, M.B.; Uemura, Y.J.; Morosan, E.
A quantum critical point (QCP) occurs upon chemical doping of the weak itinerant ferromagnet Sc3.1In. Remarkable for a system with no local moments, the QCP is accompanied by non-Fermi liquid behavior, manifested in the logarithmic divergence of the specific heat both in the ferro-and the paramagnetic states, as well as linear temperature dependence of the low-temperature resistivity. With doping, critical scaling is observed close to the QCP, as the critical exponents δ, γ, and β have weak composition dependence, with δ nearly twice and β almost half of their respective mean-field values. The unusually large paramagnetic moment μPM∼1.3μB/F.U. is nearly composition independent. Evidence for strong spin fluctuations, accompanying the QCP at xc=0.035±0.005, may be ascribed to the reduced dimensionality of Sc3.1In, associated with the nearly one-dimensional Sc-In chains.
Phonon softening and atomic modulations in ${\mathrm{EuAl}}_{4}$
(American Physical Society, 2024) Korshunov, A. N.; Sukhanov, A. S.; Gebel, S.; Pavlovskii, M. S.; Andriushin, N. D.; Gao, Y.; Moya, J. M.; Morosan, E.; Rahn, M. C.
EuAl4 is a rare-earth intermetallic in which competing itinerant and/or indirect exchange mechanisms give rise to a complex magnetic phase diagram, including a centrosymmetric skyrmion lattice. These phenomena arise not in the tetragonal parent structure but in the presence of a charge-density wave (CDW), which lowers the crystal symmetry and renormalizes the electronic structure. Microscopic knowledge of the corresponding atomic modulations and their driving mechanism is a prerequisite for a deeper understanding of the resulting equilibrium of electronic correlations and how it might be manipulated. Here, we use synchrotron single-crystal x-ray diffraction, inelastic x-ray scattering, and lattice-dynamics calculations to clarify the origin of the CDW in EuAl4. We observe a broad softening of a transverse acoustic phonon mode that sets in well above room temperature and, at 𝑇CDW=142 K, freezes out in an atomic displacement mode described by the superspace group 𝐼⁢𝑚⁡𝑚⁡𝑚⁡(00⁢𝛾)⁢𝑠⁢00. In the context of previous work, our observation is a clear confirmation that the CDW in EuAl4 is driven by electron-phonon coupling. This result is relevant for a wider family of BaAl4 and ThCr2⁢Si2-type rare-earth intermetallics known to combine CDW instabilities and complex magnetism.
Possible Mott transition in layered Sr2Mn3As2O2ﾠsingle crystals
(American Physical Society, 2019) Chen, Chih-Wei; Wang, Weiyi; Loganathan, Vaideesh; Carr, Scott V.; Harriger, Leland W.; Georgen, C.; Nevidomskyy, Andriy H.; Dai, Pengcheng; Huang, C.-L.; Morosan, E.
Single crystals of Sr2Mn3As2O2 have been grown for the first time, for which we show a possible layer-selective Mott insulator behavior. This compound stands out as a hybrid structure of MnO2 and MnAs layers, analogously to the active CuO2 and FeAs layers, respectively, in the cuprate and iron-based high-temperature superconductors. Electrical transport, neutron diffraction measurements, together with density functional theory calculations on Sr2Mn3As2O2 single crystals converge toward a picture of independent magnetic order at T1∼79 K and T2∼360 K for the two Mn sublattices, with insulating behavior at odds with the metallic behavior predicted by calculations. Furthermore, our inelastic neutron-scattering studies of spin-wave dispersions for the Mn(1) sublattice reveal an effective magnetic exchange coupling of SJ∼3.7 meV. This is much smaller than those for the Mn(2) sublattice.
Pressure effects in the itinerant antiferromagnetic metal TiAu
(American Physical Society, 2017) Wolowiec, C.T.; Fang, Y.; McElroy, C.A.; Jeffries, J.R.; Stillwell, R.L.; Svanidze, E.; Santiago, J.M.; Morosan, E.; Weir, S.T.; Vohra, Y.K.; Maple, M.B.
We report the pressure dependence of the Néel temperature T N up to P ≈ 27 GPa for the recently discovered itinerant antiferromagnet (IAFM) TiAu. The T N ( P ) phase boundary exhibits unconventional behavior in which the Néel temperature is enhanced from T N ≈ 33 K at ambient pressure to a maximum of T N ≈ 35 K occurring at P ≈ 5.5 GPa. Upon a further increase in pressure, T N is monotonically suppressed to ∼ 22 K at P ≈ 27 GPa. We also find a crossover in the temperature dependence of the electrical resistivity ρ in the antiferromagnetic (AFM) phase that is coincident with the peak in T N ( P ) , such that the temperature dependence of ρ = ρ 0 + A n T n changes from n ≈ 3 during the enhancement of T N to n ≈ 2 during the suppression of T N . Based on an extrapolation of the T N ( P ) data to a possible pressure-induced quantum critical point, we estimate the critical pressure to be P c ≈ 45 GPa.

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