15 results on '"M. M. Koza"'
Search Results
2. Quantum critical spin-liquid-like behavior in the S=12 quasikagome-lattice compound CeRh1−xPdxSn investigated using muon spin relaxation and neutron scattering
- Author
-
Rajesh Tripathi, D. T. Adroja, C. Ritter, Shivani Sharma, Chongli Yang, A. D. Hillier, M. M. Koza, F. Demmel, A. Sundaresan, S. Langridge, Wataru Higemoto, Takashi U. Ito, A. M. Strydom, G. B. G. Stenning, A. Bhattacharyya, David Keen, H. C. Walker, R. S. Perry, Francis Pratt, Qimiao Si, and T. Takabatake
- Published
- 2022
3. Strong renormalization of Ba vibrations in thermoelectric type-IX clathrate Ba24Ge100
- Author
-
R. Viennois, M. Beaudhuin, and M. M. Koza
- Published
- 2022
4. Muon spin rotation and neutron scattering investigations of the B -site ordered double perovskite Sr2DyRuO6
- Author
-
Duc Le, Ronald I. Smith, M. M. Koza, A. Sundaresan, Adrian D. Hillier, Sean Langridge, Shivani Sharma, D. T. Adroja, C. V. Tomy, C. Ritter, and Ravi Pratap Singh
- Subjects
Physics ,Magnetic moment ,Condensed matter physics ,Magnetic structure ,Relaxation (NMR) ,02 engineering and technology ,Muon spin spectroscopy ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic susceptibility ,Paramagnetism ,Spin wave ,0103 physical sciences ,Antiferromagnetism ,010306 general physics ,0210 nano-technology - Abstract
The magnetic ground state of the B -site ordered double perovskite S r 2 DyRu O 6 has been investigated using muon spin rotation and relaxation (µSR), neutron powder diffraction (NPD), and inelastic neutron scattering (INS), in addition to heat capacity and magnetic susceptibility (AC and DC) measurements. A clear signature of a long-range ordered magnetic ground state has been observed in the heat capacity data, which exhibits two sharp anomalies at 39.5 and 36 K found as well in the magnetic data. Further supporting evidence consistent with long-range magnetic ordering comes from a sharp drop in the muon initial asymmetry and a peak in the relaxation rate at 40 K, along with a weak anomaly near 36 K. Based on temperature dependent NPD, the low temperature magnetic structure contains two interpenetrating lattices of D y 3 + and Ru 5 + , forming an antiferromagnetic ground state below 39.5 K with magnetic propagation vector k = ( 0 , 0 , 0 ) . The magnetic moments of D y 3 + and Ru 5 + at 3.5 K are pointing along the crystallographic b axis with values of μ Dy = 4.92 ( 10 ) μ B and μ Ru = 1.94 ( 7 ) μ B , respectively. The temperature dependence of the Ru 5 + moments follows a mean field type behavior, while that of the D y 3 + moments exhibits a deviation indicating that the primary magnetic ordering is induced by the order of the 4 d electrons of Ru 5 + rather than that of the proper 4 f D y 3 + electrons. The origin of the second anomaly observed in the heat capacity data at 36 K must be connected to a very small spin reorientation as the NPD studies do not reveal any clear change in the observed magnetic Bragg peaks’ positions or intensities between these two transitions. INS measurements reveal the presence of crystal field excitations (CEF) in the paramagnetic state with overall CEF splitting of 73.8 meV, in agreement with the point change model calculations, and spin wave excitations below 9 meV at 7 K. Above T N , the spin wave excitations transform into a broad diffuse scattering indicating the presence of short-range dynamic magnetic correlations.
- Published
- 2020
5. Self- and interdiffusion in dilute liquid germanium-based alloys
- Author
-
H, Weis, F, Kargl, M, Kolbe, M M, Koza, T, Unruh, and A, Meyer
- Abstract
Self- and inter-diffusion coefficients in liquid Ge and dilute Ge-based Ge-Si, Ge-Au, Ge-In, Ge-Ce and Ge-Gd alloys-containing 2 at% additions, respectively, are measured using a comprehensive approach of measuring techniques: quasi-elastic neutron scattering, in situ long-capillary experiments combined with x-ray radiography, and a long-capillary experiment under microgravity conditions. Resulting inter- and Ge self-diffusion coefficients are equal within error bars for each investigated alloy. The interdiffusion coefficients are smaller for the alloys containing Ce and Gd, However, no dependence of the atomic mass of the minor additions, that varies by about a factor of seven between Si and Au, on the diffusion coefficients could be observed. This demonstrates that in a loosely-packed metallic liquid with fast diffusive dynamics the diffusion mechanism is highly collective in nature.
- Published
- 2019
6. Vibrational dynamics of the type-I clathrates A8Sn44□2 (A = Cs, Rb, K) from lattice-dynamics calculations, inelastic neutron scattering, and specific heat measurements
- Author
-
Christophe Candolfi, Yu. Grin, M. M. Koza, Wilder Carrillo-Cabrera, Frank Steglich, Michael Baitinger, Umut Aydemir, Aydemir, Umut (ORCID 0000-0003-1164-1973 & YÖK ID 58403), Candolfi, C., Koza, M. M., Carrillo-Cabrera, W., Grin, Yu., Steglich, F., Baitinger, M., Koç University AKKİM Boron-Based Materials & High-technology Chemicals Research & Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM), College of Sciences, and Department of Chemistry
- Subjects
Physics, applied ,010302 applied physics ,Materials science ,Phonon ,Clathrate hydrate ,Ab initio ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Alkali metal ,01 natural sciences ,Molecular physics ,Spectral line ,Inelastic neutron scattering ,Disorder phase-transition ,Electronic band-structure ,Thermal-conductivity ,Thermoelectric properties ,Microscopic dynamics ,Raman-spectroscopy ,Crystal ,Excitations ,Efficiency ,Condensed Matter::Materials Science ,chemistry ,Caesium ,Vacancy defect ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,0210 nano-technology - Abstract
We report on a joint theoretical and experimental study of the vibrational dynamics of the type-I clathrates A(8)Sn(44)square (2) (A=K, Rb, Cs, and square stands for a vacancy) by high-resolution inelastic neutron scattering experiments combined with low-temperature specific heat measurements (2-300K). Ab initio lattice dynamics calculations were performed on hypothetical vacancy-free A(8)Sn(46) clathrates in order to determine the phonon dispersions and vibrational density of states Z ( omega ). The temperature dependence of the generalized vibrational density of states (GVDOS) was traced from 420K down to 50K, paying particular attention to the low-energy region of the GVDOS spectra. In the Cs and Rb compounds, the inelastic signal at low energies is dominated by several peaks mainly associated with the dynamics of the alkali metal atoms A in the polyhedral cages of the clathrate structure. In contrast, the low-energy spectrum of the K compound features a more pronounced contribution of the weighed modes of the framework Sn atoms. Upon cooling, the A-weighted modes soften regardless of the nature of the alkali element. The shift observed is similar for the three compounds and of small amplitude, suggestive of a dominant quasi-harmonic behavior above 50K. The distinct dynamics of the K atoms in comparison to Cs and Rb is further demonstrated by the analyses of the low-temperature specific heat data, indicating that the low-energy Sn-weighted modes cannot be described by a Debye model with Einstein-like contributions., CNRS-MPG Program
- Published
- 2020
7. Absence of a long-range ordered magnetic ground state in Pr
- Author
-
Harikrishnan S, Nair, Michael O, Ogunbunmi, S K, Ghosh, D T, Adroja, M M, Koza, T, Guidi, and A M, Strydom
- Abstract
Signatures of absence of a long-range ordered magnetic ground state down to 0.36 K are observed in magnetic susceptibility, specific heat, thermal/electrical transport and inelastic neutron scattering data of the quasi-skutterudite compound Pr
- Published
- 2018
8. Understanding the magnetism in noncentrosymmetric CeIrGe3: Muon spin relaxation and neutron scattering studies
- Author
-
Gilles André, Pascal Manuel, M. M. Koza, D. T. Adroja, Adrian D. Hillier, Stéphane Rols, Dmitry D. Khalyavin, and V. K. Anand
- Subjects
Physics ,Magnetic structure ,Magnetic moment ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter - Superconductivity ,Neutron diffraction ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Heat capacity ,Magnetic susceptibility ,Inelastic neutron scattering ,Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,Antiferromagnetism ,010306 general physics ,0210 nano-technology ,Controlling collective states ,Energy (signal processing) - Abstract
The magnetic properties of a pressure induced noncentrosymmetric heavy-fermion superconductor CeIrGe$_3$ have been investigated by muon spin relaxation ($\mu$SR), powder neutron diffraction (ND) and inelastic neutron scattering (INS) techniques at ambient pressure. For completeness we have also measured the ac magnetic susceptibility $\chi_{\rm ac}(T)$, dc magnetic susceptibility $\chi(T)$, dc isothermal magnetization $M(H)$ and heat capacity $C_{\rm p}(T,H)$ down to 2 K. CeIrGe$_{3}$ is known to exhibit pressure induced superconductivity ($T_{\rm c}\approx 1.5$ K) at a pressure of 20 GPa and antiferromagnetic ordering at 8.7 K, 4.7 K and 0.7 K at ambient pressure. Our $\chi_{\rm ac}(T)$ and $\chi(T)$ data show an additional anomaly near 6.2 K which is also captured in $C_{\rm p}(T)$ data. From $\chi_{\rm ac}(T)$, $\chi(T)$ and $C_{\rm p}(T)$ measurements we infer three antiferromagnetic transitions above 2 K at $T_{\rm N1}= 8.5$ K, $T_{\rm N2}= 6.0$ K and $T_{\rm N3}= 4.6$ K. Our $\mu$SR study also confirms the presence of three transitions through the observation of one frequency for $T_{\rm N2} < T\leq T_{\rm N1}$, two frequencies for $T_{\rm N3} < T\leq T_{\rm N2}$ and three frequencies for $T\leq T_{\rm N3}$ in the oscillatory asymmetry. The ND data reveal an incommensurate nature of the magnetic ordering at $T=7$ K with the propagation vector k = (0,0,0.688(3)), and a commensurate magnetic structure at $T=1.5$ K with the propagation vector locked to the value k = (0,0,2/3) and magnetic moments oriented along the $c$ axis. The commensurate structure couples a macroscopic ferromagnetic component, resulting in a strong dependence of the lock-in transition temperature on external magnetic field. The INS data show two well defined crystal electric field (CEF) excitations arising from the CEF-split Kramers doublet ground state of Ce$^{3+}$., Comment: 13 pages, 16 figures, 1 table
- Published
- 2018
- Full Text
- View/download PDF
9. Contrasting effect of La substitution on the magnetic moment direction in the Kondo semiconductorsCeT2Al10(T=Ru,Os)
- Author
-
Adrian D. Hillier, M. M. Koza, Jo Kawabata, Dmitry D. Khalyavin, P. Peratheepan, Toshiro Takabatake, D. T. Adroja, André M. Strydom, B. Fåk, Y. Okada, Jon W. Taylor, Amitava Bhattacharyya, Yuji Muro, C. Ritter, and Yoshihiro Yamada
- Subjects
Physics ,Magnetic anisotropy ,Condensed matter physics ,Magnetic moment ,Kondo insulator ,Order (ring theory) ,Antiferromagnetism ,Muon spin spectroscopy ,Condensed Matter Physics ,Ground state ,Inelastic neutron scattering ,Electronic, Optical and Magnetic Materials - Abstract
The opening of a spin gap in the orthorhombic compounds CeT$_2$Al$_{10}$ (T = Ru and Os) is followed by antiferromagnetic ordering at $T_N$ = 27 K and 28.5 K, respectively, with a small ordered moment (0.29$-$0.34$\mu_B$) along the $c-$axis, which is not an easy axis of the crystal field (CEF). In order to investigate how the moment direction and the spin gap energy change with 10\% La doping in Ce$_{1-x}$La$_x$T$_2$Al$_{10}$ (T = Ru and Os) and also to understand the microscopic nature of the magnetic ground state, we here report on magnetic, transport, and thermal properties, neutron diffraction (ND) and inelastic neutron scattering (INS) investigations on these compounds. Our INS study reveals the persistence of spin gaps of 7 meV and 10 meV in the 10\% La-doped T = Ru and Os compounds, respectively. More interestingly our ND study shows a very small ordered moment of 0.18 $\mu_B$ along the $b-$axis (moment direction changed compared with the undoped compound), in Ce$_{0.9}$La$_{0.1}$Ru$_2$Al$_{10}$, however a moment of 0.23 $\mu_B$ still along the $c-$axis in Ce$_{0.9}$La$_{0.1}$Os$_2$Al$_{10}$. This contrasting behavior can be explained by a different degree of hybridization in CeRu$_2$Al$_{10}$ and CeOs$_2$Al$_{10}$, being stronger in the latter than in the former. Muon spin rotation ($\mu$SR) studies on Ce$_{1-x}$La$_x$Ru$_2$Al$_{10}$ ($x$ = 0, 0.3, 0.5 and 0.7), reveal the presence of coherent frequency oscillations indicating a long$-$range magnetically ordered ground state for $x$ = 0 to 0.5, but an almost temperature independent Kubo$-$Toyabe response between 45 mK and 4 K for $x$ = 0.7. We will compare the results of the present investigations with those reported on the electron and hole$-$doping in CeT$_2$Al$_{10}$.
- Published
- 2015
10. Muon spin rotation and neutron scattering study of the noncentrosymmetric tetragonal compoundCeAuAl3
- Author
-
M. M. Koza, Alberto Fraile, Adrian D. Hillier, A. del Moral, J. W. Taylor, Enrique Burzurí, C. de la Fuente, J. I. Arnaudas, Winfried Kockelmann, Aziz Daoud-Aladine, D. T. Adroja, Fernando Luis, Science and Technology Facilities Council (UK), European Commission, Diputación General de Aragón, and Ministerio de Ciencia e Innovación (España)
- Subjects
Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,FOS: Physical sciences ,Muon spin spectroscopy ,Condensed Matter Physics ,Coupling (probability) ,Magnetic susceptibility ,Heat capacity ,Inelastic neutron scattering ,Electronic, Optical and Magnetic Materials ,Condensed Matter - Strongly Correlated Electrons ,Paramagnetism ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Energy (signal processing) - Abstract
Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al., We have investigated the noncentrosymmetric tetragonal heavy fermion compound CeAuAl3 using muon spin rotation (μSR), neutron diffraction (ND), and inelastic neutron scattering (INS) measurements. We have also revisited the magnetic, transport, and thermal properties. The magnetic susceptibility reveals an antiferromagnetic transition at 1.1 K with, possibly, another magnetic transition near 0.18 K. The heat capacity shows a sharp λ-type anomaly at 1.1 K in zero field, which broadens and moves to a higher temperature in an applied magnetic field. Our zero-field μSR and ND measurements confirm the existence of a long-range magnetic ground state below 1.2 K. Further, the ND study reveals an incommensurate magnetic order with a magnetic propagation vector k=(0,0,0.52(1)) and a spiral structure of Ce moments coupled ferromagnetically within the ab plane. Our INS study reveals the presence of two well-defined crystal electric field (CEF) excitations at 5.1 and 24.6 meV in the paramagnetic phase of CeAuAl3 that can be explained on the basis of the CEF theory and the Kramer's theorem for a Ce ion having a 4f1 electronic state. Furthermore, low energy quasielastic excitations show a Gaussian line shape below 30 K compared to a Lorentzian line shape above 30 K, indicating a slowdown of spin fluctuations below 30 K. We have estimated a Kondo temperature of TK=3.5K from the quasielastic linewidth, which is in good agreement with that estimated from the heat capacity. This study also indicates the absence of any CEF-phonon coupling unlike that observed in isostructural CeCuAl3 The CEF parameters, energy level scheme, and their wave functions obtained from the analysis of INS data explain satisfactorily the single crystal susceptibility in the presence of two-ion anisotropic exchange interaction in CeAuAl3., We are grateful for funding by the Centre for Materials Physics and chemistry-Science and technology facilities council (CPMC-STFC) (Grant No. CMPC-09108), EU-FEDER (Grants No. MAT2009-10040, No. MAT2012-31309, and No. DGA-E81) and Fondo Social Europeo.
- Published
- 2015
11. Inelastic neutron scattering study of the lattice dynamics in the clathrate compound BaGe5
- Author
-
Frank Steglich, M. M. Koza, Michael Baitinger, Yu. Grin, Christophe Candolfi, and Umut Aydemir
- Subjects
Lattice dynamics ,Range (particle radiation) ,Materials science ,Phonon ,Clathrate hydrate ,Clathrate compound ,Nanotechnology ,Crystal structure ,Condensed Matter Physics ,Molecular physics ,Inelastic neutron scattering ,chemistry.chemical_compound ,chemistry ,General Materials Science ,Crystallite - Abstract
We report inelastic neutron scattering (INS) measurements on the polycrystalline oP60-type clathrate BaGe_5, whose crystal structure is related to the type-I clathrate Ba8Ge_(43□3) and to the cP124-clathrate Ba_6Ge_(25). Our results show that BaGe_5 exhibits a similar phonon density of states (PDOS) in the energy range 0–40 meV with respect to Ba8Ge_(43□3). The low-energy region of the PDOS spectrum (0–10 meV) consists of two peaks at 4.1 and 6.2 meV likely related to Ba-weighted modes. Compared to Ba8Ge_(43□3), the low-energy region of the phonon spectrum of BaGe_5 shows a more complex structure, likely reflecting the presence of three distinct crystallographic sites for Ba. The specific heat data of BaGe_5, reexamined in light of the INS results, indicate that the Ba-weighted modes dominate the low-temperature behavior of C_p.
- Published
- 2015
12. Ferromagnetic fluctuations in YbNi4P2 measured by inelastic neutron scattering
- Author
-
Giovanna G. Simeoni, Jan Peter Embs, M. M. Koza, Zita Huesges, Cornelius Krellner, Oliver Stockert, Tom Fennell, and C. Geibel
- Subjects
History ,Materials science ,Condensed matter physics ,Inelastic scattering ,Neutron scattering ,Small-angle neutron scattering ,Inelastic neutron scattering ,Computer Science Applications ,Education ,Neutron spectroscopy ,Condensed Matter::Materials Science ,Ferromagnetism ,Quasielastic neutron scattering ,Curie temperature ,Condensed Matter::Strongly Correlated Electrons - Abstract
YbNi4P2 is one of the very few heavy-fermion systems which allow the study of ferromagnetic quantum criticality. The Curie temperature TC=0.17 K can be suppressed by substituting arsenic on the phosphorus site, without changing the ferromagnetic nature of the ordered state. The ordered moment, even of the unsubstituted compound, is only around 0.05 μB, which hinders elastic neutron scattering experiments. To gain microscopic insight into the nature of the interactions, we have studied the magnetic excitations of polycrystalline YbNi4P2 by time-of-flight neutron spectroscopy. For momentum transfers larger than about 0.6 A−1 we find a quasi-elastic response whose width at low temperatures is limited by the Kondo effect. In contrast, the low-energy magnetic response is distinctly different for Q approaching zero: At low temperatures, but still in the paramagnetic phase, susceptibility and lifetime of the spin fluctuations are strongly enhanced, indicating the proximity of ferromagnetism.
- Published
- 2015
13. Inelastic neutron scattering study of the lattice dynamics in the clathrate compound BaGe5.
- Author
-
C Candolfi, U Aydemir, M M Koza, M Baitinger, Yu Grin, and F Steglich
- Published
- 2015
- Full Text
- View/download PDF
14. Temperature-dependent dynamic structure factors for liquid water inferred from inelastic neutron scattering measurements.
- Author
-
Noguere G, Scotta JP, Xu S, Farhi E, Ollivier J, Calzavarra Y, Rols S, Koza M, and Marquez Damian JI
- Abstract
Temperature-dependent dynamic structure factors S(Q, ω) for liquid water have been calculated using a composite model, which is based on the decoupling approximation of the mean square displacement of the water molecules into diffusion and solid-like vibrational parts. The solid-like vibrational part S
vib (Q, ω) is calculated with the phonon expansion method established in the framework of the incoherent Gaussian approximation. The diffusion part Sdiff (Q, ω) relies on the Egelstaff-Schofield translational diffusion model corrected for jump diffusions and rotational diffusions with the Singwi-Sjölander random model and Sears expansion, respectively. Systematics of the model parameters as a function of temperature were deduced from quasi-elastic neutron scattering data analysis reported in the literature and from molecular dynamics (MD) simulations relying on the TIP4P/2005f model. The resulting S(Q, ω) values are confronted by means of Monte Carlo simulations to inelastic neutron scattering data measured with IN4, IN5, and IN6 time-of-flight spectrometers of the Institut Laue-Langevin (ILL) (Grenoble, France). A modest range of temperatures (283-494 K) has been investigated with neutron wavelengths corresponding to incident neutron energies ranging from 0.57 to 67.6 meV. The neutron-weighted multiphonon spectra deduced from the ILL data indicate a slight overestimation by the MD simulations of the frequency shift and broadening of the librational band. The descriptive power of the composite model was suited for improving the comparison to experiments via Bayesian updating of prior model parameters inferred from MD simulations. The reported posterior temperature-dependent densities of state of hydrogen in H2 O would represent valuable insights for studying the collective coupling interactions in the water molecule between the inter- and intramolecular degrees of freedom.- Published
- 2021
- Full Text
- View/download PDF
15. Lattice dynamics in intermetallic Mg2Ge and Mg2Si.
- Author
-
Bessas D, Simon RE, Friese K, Koza M, and Hermann RP
- Abstract
The lattice dynamics of polycrystalline Mg(2)Ge and Mg(2)Si are compared using both microscopic and macroscopic measurements as well as theoretical calculations. The volume thermal expansion coefficient between 200 and 300 K was found to be 4.37(5) · 10(-5) K(-1) in Mg(2)Ge, compared to 3.69(5) · 10(-5) K(-1) in Mg(2)Si. Inelastic neutron scattering measurements yield densities of phonon states which are in line with theoretical calculations. The microscopic data were corroborated with macroscopic calorimetry measurements and provide quantified values for anharmonicity. The estimated macroscopic Grüneisen parameter is, γ(Mg(2)Si) = 1.17(5) and γ(Mg(2)Ge) = 1.46(5) at 295 K, in excellent agreement with Raman scattering data. Although the element specific mean force constants are practically the same, in Mg(2)Ge and Mg(2)Si, a mass homology relation alone cannot reproduce the difference in the partial densities of vibrational states in these compounds and differences in elemental bonding should be taken into account.
- Published
- 2014
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.