Search

We have conducted inelastic neutron scattering measurements to investigate the crystal-electric-field (CEF) levels associated with Pr3+ 4 f 2 -electron configuration in the PrTr2X20 (Tr: transition metal, X: Al and Zn). Hybridization between conduction electrons and 4 f electrons has been deduced from the spectral widths, which is a key factor for understanding the anomalous low-temperature transport properties and the ordering phase transitions in the PrTr2X20. We also discuss structural-transition effects on local symmetries of the Pr-ion sites.

Professor Nobuyoshi Wakabayashi passed away on May 12, 2017, at the age of 79. He was a leading scientist in neutron scattering on condensed-matter physics at Oak Ridge National Laboratory (ORNL), ...

The metal–nonmetal transition of PrRu4P12 has been investigated utilizing the resonant X-ray scattering technique. Strong resonant signals at the Pr M4,5 and P K edges revealed the spatial modulati...

Structural studies were performed on ${R}_{3}{\mathrm{Rh}}_{4}{\mathrm{Sn}}_{13}$ ($R$=La and Ce). X-ray diffraction measurements on single-crystalline samples of both Rh-based compounds, which were synthesized by the molten Sn-flux method, have revealed structural transformations below ${T}_{\mathrm{D}}\ensuremath{\simeq}$ 350 K. The low-temperature superstructures are characterized by the wave vector $\mathbit{q}=(1/2,1/2,0)$. The space group in the low-temperature phases of both compounds is chiral cubic $I{2}_{1}3$, which is the same as that of ${R}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$ ($R$=La and Ce). Neutron diffraction measurement of ${\mathrm{Ce}}_{3}{\mathrm{Rh}}_{4}{\mathrm{Sn}}_{13}$ revealed no magnetic long-range order below the temperature of the specific-heat peaks at 1.2 and 1.8 K. The low-temperature magnetic state in the chiral phase is that of a paramagnetic semimetal, whereas the dynamical spin correlation of Ce is deduced from the specific-heat data, as found previously in ${\mathrm{Ce}}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$.

Spin-state transition, also known as spin crossover, plays a key role in diverse systems, including minerals and biological materials. In theory, the boundary range between the low- and high-spin states is expected to enrich the transition and give rise to unusual physical states. However, no compound that realizes a nearly degenerate critical range as the ground state without requiring special external conditions has yet been experimentally identified. This study reports that, by comprehensive measurements of macroscopic physical properties, X-ray diffractometry, and neutron spectroscopy, the Sc substitution in LaCoO$_3$ destabilizes its nonmagnetic low-spin state and generates an anomalous paramagnetic state accompanied by the enhancement of transport gap and magneto-lattice-expansion as well as the contraction of Co--O distance with the increase of electron site-transfer. These phenomena are not well described by the mixture of conventional low- and high-spin states, but by their quantum superposition occurring on the verge of a spin-state transition. The present study enables us to significantly accelerate the design of new advanced materials without requiring special equipment based on the concept of quantum spin-state criticality., Keywords: excitonic insulator, bi-exciton

We studied the effect of magnetic Nd-ion substitution on the metal-nonmetal transition at a transition temperature of 63 K of PrRu4P12, which is characterized by antiferro-type electric multipole ordering of Pr-ion 4f electrons. The transition temperature of Pr1-xNdxRu4P12 depends weakly on the Nd concentration x as compared to Laand Ce-substituted compounds. Inelastic neutron-scattering measurements revealed that the energies and widths of crystalline field excitation peaks of Pr 4f 2 in Pr0.85Nd0.15Ru4P12 are very similar to those of PrRu4P12. These experimental results indicate that the ordered state is robust against the substitution of magnetic Nd ions as compared to the La and Ce substitutions. Magnetic interactions between the Pr ions and the Nd ions in Pr1-xNdxRu4P12 help stabilize the magnetic triplet ground state of the Pr ions that appears in the antiferro-type multipole ordered phase. Therefore, the nonmagnetic multipole ordered phase of PrRu4P12 is compatible with the magnetic perturbation., Conference : 20th International Conference on Magnetism, ICM 2015, Location : Barcelona, SPAIN, Date : JUL 05-10, 2015

Inelastic neutron scattering experiments have been conducted to investigate the spin dynamics and crystal-electric-field level scheme of the Ce $4f$ electrons in ${\mathrm{Ce}}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$. This compound exhibits a large specific heat at low temperatures and anomalous semimetallic transport in the chiral crystallographic phase below 160 K. Distinctly observed magnetic excitations at approximately 6 and 29 meV are asymmetric in spectral shape and are reproduced by two inequivalent crystal-electric-field splitting schemes, which are deduced from the chiral structure. We have also observed the spin dynamics reflecting antiferromagnetic correlations below 1 meV, which is enhanced with an upturn in the electrical resistivity below 15 K and which yields a low-energy density of state relevant to the large specific heat. We discuss the possibility of a three-dimensional Weyl semimetal state, considering the chiral-lattice symmetry, electronic hybridization, and magnetic correlation.

Neutron diffraction measurements conducted under applied magnetic fields evidence the ordered structure of ${\mathrm{PrIr}}_{2}{\mathrm{Zn}}_{20}$ below approximately 0.1 K. A two-channel (orbital) Kondo effect is expected to act within the non-Kramers doublet ground state of the Pr $4f$ electrons of this material in cubic symmetry. Antiferromagnetic reflections are clearly induced under the influence of applied magnetic fields, which are characterized by the propagation vector $\mathbit{q}=(1/2,1/2,1/2)$. This result indicates antiferromagnetic-type ordering of the Pr $f$-electron multipoles. The ${\mathrm{\ensuremath{\Gamma}}}_{3}$-type quadrupole, ${O}_{2}^{2}$, is the dominant order parameter deduced from the observed magnetic structure factor. We also discuss the entanglement of various finite-magnitude multipoles up to third rank, which are relevant to the low-energy crystalline-electric-field split levels in this material.

The degrees of freedom of electron multipoles in various rare-earth alloy compounds have been investigated over the last four decades. Recently, it has been found that the multipole orderings accom...

The magnetic structure of YbPd was determined for a newly synthesized strain-free sample by neutron diffraction techniques. The sinusoidal magnetic structure characterized by an incommensurate wave...

PrFe4P12shows an anomalously phase transition from a heavy fermion (HF) state to a non-magnetic ordered state. We prepared single crystal sample of Pr (Fe1-xCox)4P12by Sn-flux method to investigate the effects of electron doping. The distinct change of magnetic property was observed. The phase transition of PrFe4P12rapidly disappears when doped rate x=0.03. This result indicates that the d-electron plays an important role in formation of Low-temperutre phase and HF state of PrFe4P12.

The compounds designated as ${R}_{3}{T}_{4}{\mathrm{Sn}}_{13}$ ($R$ = rare earth and $T$ = transition metal) are hypothesized to be strongly correlated electron systems. Some of these compounds exhibit structural phase transitions with speculated charge-density-wave (CDW) formations. We carried out x-ray diffraction measurements in order to investigate the second-order phase transition of ${R}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$ ($R=\mathrm{La} \text{and} \mathrm{Ce}$) by using single-crystalline samples synthesized by the molten Sn-flux method. Both compounds exhibit the structural superlattice transformations characterized by the wave vector $\mathbit{q}=(1/2,1/2,0)$ below ${T}_{\mathrm{D}}\ensuremath{\simeq}160$ K, which originate from electronic states owing to the common Co and Sn. The space group of the low-temperature phase is evidenced as a chiral cubic $I{2}_{1}3$. The magnetic-susceptibility enhancement and the Co-ion valence shift below ${T}_{\mathrm{D}}$ are signatures of a phase transition not fully attributed to the conventional CDW formation.

Using a transportable 3 He spin filter neutron polariser, we have constructed a polarised thermal neutron diffraction (PND) instrument on a powder neutron diffractometer. To minimise the inhomogeneity of the magnetic fields around the 3 He spin filter, an optimised compact non-adiabatic two-coil spin flipper for the PND instrument was developed. Magnetic field criteria were discussed for the design of the flipper. Using the PND instrument with the flipper, we succeeded in observing a difference in the magnetic field dependence of the deposited ferromagnetic phases in nanocomposite materials.

Magnetic structure on SrMnO3 films has been investigated utilizing neutron magnetic scattering technique. We have succeeded in detecting a magnetic signal at (0.5 0.5 0.5) associated with G-type antiferromagnetic order. The temperature dependence of the signal intensity indicates a second-order transition with the transition temperature, T N ~ 190 K . This is a first step of our study of the magnetism in the manganite thin film system.

PrOs 4 Sb 12 is the first Pr-based heavy fermion superconductor exhibiting intriguing behavior both in the superconducting and normal states. To clarify the origin of the behavior, intensive studies have been made by variety of experimental techniques. As a result of intensive studies, the normal state properties have been mostly clarified, however, there still remain important questions on the superconducting state of this material. We discuss the present status of the understanding of superconducting state in relation with the normal state properties of this material.

The magnetic ordered state of a single-crystal sample of TbB6 has been studied with the high-precision neutron diffraction instrument SENJU installed at BL18 of the Materials and Life Science Facil...

PrRu4P12, which undergoes a metal-insulator transition at TMI ~ 63 K, has been investigated by resonant x-ray scattering technique at the Pr L 3-edge, the P K-edge, and the Ru L 3-edge, in which element and orbital selective electronic states can be clarified. Resonating energy spectra at the 111 reflection were found at the Pr L 3-edge and P K-edge, while it was not observed at the Rh L 3-edge. This is the first observation of quite large resonant signal at the P K-edge. This result is considered as a direct evidence for the strong Pr 4f and P 3p hybridization effect on the unconventional ordered phase accompanied by the insulator state.

Full varieties of strongly correlated electron phenomena have been found in the filled skutterudite systems, by changing the constituent elements. The unique crystal structure leads to novel features even in the systems containing rare earth elements with plural number of 4 f -electrons. According to the intensive competitions and cooperation among experimental and theoretical research works, remarkable progress has been made in sorting out several basic origins that bring about the variety of this system, such as the strong c – f hybridization, the small CEF level splitting, the orbital degree of freedom (multipoles), and the positional degree of freedom within a pnictogen cage. However, there still remain many attractive questions to be answered.

We review inelastic neutron scattering experiments performed on single crystal of the heavy fermion superconductor PrOs 4 Sb 12 . The low lying excitation spectrum consist of a singlet–triplet crystal field transition modulated by quadrupolar intersite interactions. The evolution of this so-called quadrupolar exciton on crossing the superconducting transition was studied both as a function of temperature and magnetic field. Our measurements point out the coupling between the quadrupolar fluctuations and the superconductivity.

Neutron diffraction experiments have been performed to investigate the electronic phase transitions in the Pr-based filled skutterudite PrFe 4 P 12 . This compound undergoes a transition from a characteristic heavy-electron state to a nonmagnetic phase below 6.5 K. Neutron diffraction experiments reveal an antiferromagnetic alignment of the magnetic-field induced dipole moments. The directions of the antiferromagnetic components are considered to be always parallel to the magnetic field applied along either [0 0 1], [1 1 0] or [1 1 1]. This implies that the symmetry of the ordered state can be categorized as Γ 1 . This phenomenon is consistent with the scenario of a scalar-type order parameter for the Pr 4 f electron state.

The resonant and non-resonant X-ray scattering technique have been applied to the observation of a valence fluctuated (VF) state in R 4 As 3 ( R = Yb and Eu). In Yb 4 As 3 , the resonant signal reflecting a short range order of the charge ordering of Yb ions was clearly found at Yb L 3 -edge in the VF state above the charge ordering temperature. This is the first observation of the spatial correlation of the valences in the VF state. The valence state in Eu 4 As 3 was also investigated near Eu L 3 -edge for comparison.

In the filled skutterudite compounds (RT 4 X 12 : R rare earth, T=Fe, Ru, Os, and X=pnictogen-ions), various attractive features have been found by replacing the constituent elements, e.g., metal–insulator transition in PrRu 4 P 12 , competing heavy fermion and multipolar ordered states in PrFe 4 P 12 , heavy fermion superconductivity in PrOs 4 Sb 12 , etc. Most of these features are realized probably by the unique crystal structure; R is embedded in the cage made of 12X and eight T ions, so that the strong c–f hybridization becomes a common feature irrespective of the constituent elements. The strong c–f hybridization in skutterudites enables the strongly correlated electron behaviors even in the systems containing rare-earth elements with more than one 4f-electron. The effect of X-replacement appears most apparently as a change in c–f hybridization, as is naturally inferred from the large difference in lattice constant. In addition to the c–f hybridization effect, it was recognized that f-electron's multipolar degrees of freedom and relatively small crystalline electric field splitting are important factors to understand the aforementioned novel phenomena.

Shinichi Itoh1, Tetsuya Yokoo1, Takatsugu Masuda2, Hideki Yoshizawa2, Minoru Soda2, Yoichi Ikeda2, Soshi Ibuka1, Daichi Kawana1, Taku J. Sato3, Yusuke Nambu3, Keitaro Kuwahara4, Shin-ichiro Yano5, Jun Akimitsu5, Yoshio Kaneko6, Yoshinori Tokura6,7, Masaki Fujita8, Masashi Hase9, Kazuaki Iwasa10, Haruhiro Hiraka1, Tatsuo Fukuda11, Kazuhiko Ikeuchi12, Koji Yoshida13 Toshio Yamaguchi13, Kanta Ono1, Yasuo Endoh1,6,8 1Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba 305-0801, Japan 2The Institute for Solid State Physics, The University of Tokyo, Tokai 319-1106, Japan 3Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan 4Institute of Applied Beam Science, Ibaraki University, Mito 310-8512, Japan 5Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara 252-5258, Japan 6RIKEN Center for Emergent Matter of Science, Wako 351-0198, Japan 7Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan 8Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan 9National Institute for Materials Science, Tsukuba 305-0047, Japan 10Department of Physics, Tohoku University, Sendai 980-8578, Japan 11Quantum Beam Science Center, Japan Atomic Energy Agency, Sayo 679-5148, Japan 12Comprehensive Research Organization for Science and Society, Tokai 319-1106, Japan 13Department of Chemistry, Fukuoka University, Fukuoka 814-0180, Japan

We studied the Co valences and spin states in electron-doped LaCo$_{1-y}$Te$_{y}$O$_3$ by measuring x-ray absorption spectra and electron spin resonance. The low-temperature insulating state involves the low-spin Co$^{3+}$ ($S=0$) and the high-spin Co$^{2+}$ state, which is described by $g=3.8$ and $j_{\rm eff}=1/2$. The results, in concurrence with the electron-hole asymmetry confirmed in electrical resistivity, coincide with a spin-blockade phenomenon in this system. Further, we discuss the $g$ factor in terms of the strong covalent-bonding nature and consider multiple origins of this phenomenon., 7 pages, 5 figures, and 1 table

Recent neutron scattering studies on the Pr-based filled skutterudite compounds, which show strongly correlated phenomena, are reviewed. It was found that the 4f electron states of PrFe 4 P 12 and PrRu 4 P 12 are strongly hybridized with conduction electrons. It is consistent with the heavy-fermion properties observed for PrFe 4 P 12 . These states turn out to be the quadrupole ordering state ( PrFe 4 P 12 ) or the charge density wave state ( PrRu 4 P 12 ) at low temperatures. The lowest crystal field excited state of PrOs 4 Sb 12 was found to show an excitonic behavior, which is ascribed to the quadrupolar interaction between Pr atoms. The strong temperature dependence of the excitonic excitations through the superconducting phase transition indicates a close correlation of the excitons with the superconductivity of PrOs 4 Sb 12 . The importance of the characteristic Fermi surface topology and the effects of the p–f hybridization is discussed to understand the variety of the strongly correlated phenomena in these compounds based on the experimental results.

Spin fluctuations were studied over a wide momentum ($\ensuremath{\hbar}Q$) and energy ($E$) space in the frustrated $d$-electron heavy-fermion metal ${\mathrm{LiV}}_{2}{\mathrm{O}}_{4}$ by time-of-flight inelastic neutron scattering. We observed the overall $Q\ensuremath{-}E$ evolutions near the characteristic $Q=0.6\text{ }\text{ }{\AA{}}^{\ensuremath{-}1}\text{ }$ peak and found another weak broad magnetic peak around $2.4\text{ }\text{ }{\AA{}}^{\ensuremath{-}1}$. The data are described by a simple response function, a partially delocalized magnetic form factor, and antiferromagnetic short-range spatial correlations, indicating that heavy-fermion formation is attributable to spin-orbit fluctuations with orbital hybridization.

Electronic state evolution in the metal-non-metal transition of PrRu4P12 has been studied by X-ray and polarized neutron diffraction experiments. It has been revealed that, in the low-temperature non-metallic phase, two inequivalent crystal-field (CF) schemes of Pr3+ 4f^2 electrons with Gamma_1 and Gamma_4^(2) ground states are located at Pr1 and Pr2 sites forming the bcc unit cell surrounded by the smaller and larger cubic Ru-ion sublattices, respectively. This modulated electronic state can be explained by the p-f hybridization mechanism taking two intermediate states of 4f^1 and 4f^3. The p-f hybridization effect plays an important role for the electronic energy gain in the metal-non-metal transition originated from the Fermi surface nesting., 5 pages, 5 figures. Accepted by J. Phys. Soc. Jpn

We have succeeded in growing a high-quality single crystal of UCu 2 Si 2 with the tetragonal structure by the Sn-flux method and measured the electrical resistivity, magnetic susceptibility, magnetization and specific heat. UCu 2 Si 2 is found to order antiferromagnetically below T N =106 K, and follows a successive ferromagnetic ordering at T C =100 K. The magnetic properties are highly anisotropic, reflecting the crystal structure. An easy-axis of magnetization is found to be the [001] direction ( c -axis) both in the antiferromagnetic and ferromagnetic phases, while the [100] direction ( a -axis) corresponds to the hard-axis in magnetization. The magnetization curve in the antiferromagnetic phase indicates a clear metamagnetic transition at a low field of about 1 kOe and changes into a ferromagnetic magnetization curve below T C =100 K. The saturation moment is determined as 1.75 µ B /U at 2 K. The electronic specific heat coefficient is also determined as 20 mJ/(K 2 ·mol).

Various properties of the strongly correlated electron system CeSb at ambient pressure as well as under high pressures have been investigated employing X-ray as a probe. The satellite peaks caused by the lattice modulation of CeSb in its AFP3 phase at ambient pressure have been analyzed successfully. The satellite peak intensity pattern was explained based on a model considering different effective ionic sizes and the scattering form factors for Γ 7 and Γ 8 -like Ce 3+ ions which appear in the ordered phase. The wave function for the Γ 8 -like Ce ion with larger moment was found almost the same as that of J z =5/2, which is consistent with the neutron diffraction experiment. At high pressures above about 1.9 GPa, rapid decrease of lattice constant was found below a certain critical temperature T L , below which a sudden increase of electrical resistivity appears. This phenomenon can be explained by the formation of magnetic polaron state below this temperature.

Magnetic excitations in a single crystal of heavy-fermion superconductor PrOs 4 Sb 12 have been studied by inelastic neutron scattering (INS) at low temperatures under high magnetic fields. The crystal field (CF) excitations at 0.7 meV observed in a previous INS study of a polycrystal sample were confirmed in this study on a single crystal. The observed excitations in the zero magnetic field soften around a wave vector (1,0,0), which is the modulation vector of the field-induced antiferro-quadrupolar ordering, suggesting the presence of quadrupolar instability. The observed field dependence of excitations is better reproduced in a singlet ground-state model rather than in a non-Kramers doublet ground-state model. In a high resolution experiment, furthermore, the change of the excitation spectra at (1,0,0) was observed on passing through the superconducting transition temperature, indicating that the excitation and the superconductivity are closely related in PrOs 4 Sb 12 .

We have observed superlattice reflections from the low-carrier system CeP under high pressures up to 2 GPa and also under magnetic field up to 12.5 T by means of synchrotron X-ray diffraction. The observed intensities of superlattice reflections are well explained by a model that takes into account both the lattice and charge modulation due to the periodic arrangement of ferromagnetic double layers of Γ8-like Ce ions in the lattice of Γ7 Ce ions. A new magnetic phase with the period of nine Ce planes was found in the experiment at the magnetic field of 12.5 T.

Neutron diffraction experiments on the heavy-fermion superconductor PrOs 4 Sb 12 revealed that a small antiferromagnetic moment, parallel to [010] ( y -direction), is induced in the field-induced phase ( H ∥ z ). The analysis, based on the Γ 1 singlet ground state crystal field model, shows that antiferro-order of O y z -type quadrupole moments of Pr ions is formed in the field-induced phase. This strongly suggests that the crystal field ground-state of Pr ions in PrOs 4 Sb 12 is the Γ 1 singlet and the quadrupolar ordering is induced due to level crossing with an excited state under a magnetic field.

We studied electron-doped \(\text{LaCo}_{1 - y}\text{Te}_{y}^{6 + }\text{O}_{3}\) by magnetization measurements and neutron scattering. The effective Bohr magneton, estimated by Curie–Weiss fitting around room temperature, is independent of y. This suggests that magnetic Co3+(HS), not nonmagnetic Co3+(LS), is mainly replaced by doped magnetic Co2+(HS). At the lowest temperatures, a Brillouin-function-like saturating behavior persists in the magnetization curves even in the high-y samples, and neither a clear magnetic reflection nor magnetic dispersion is observed by neutron scattering. These findings indicate that the magnetic correlation is very weak, in contrast to the well-known hole-doped LaCoO3 accompanied by a drastic transition to a ferromagnetic metal. However, we also found that the low-y samples exhibit nonnegligible enhancement of the saturated magnetization by ∼2μB per a doped electron. All these characteristics are discussed in the light of the activation and inactivation of a spin-state bloc...

We performed measurements of specific heat and inelastic neutron scattering on Pr(Fe1-xCox)4P12 to investigate the effects of d-electron doping on the heavy fermion (HF) state and non-magnetic order state of PrFe4P12. The ordered state is suppressed by the Co substitution. A Schottky type behavior in the specific-heat appears at 8 K, in contrast with the undoped system. The inelastic neutron spectrum of the Co substituted system is composed of several sharp inelastic peaks, in contrast with the quasi-elastic spectrum in the HF phase of PrFe4P12. The experimental results indicate that the Co substitution induces localized 4f electrons of Pr ions with suppression of the HF state and the exotic ordering.

Neutron scattering studies were carried out for investigating heavy-electron-like behaviors of PrCu4Au. Excitation spectra are composed of crystal-field (CF) excitations in the Pr3+4f2 electron configuration and a broad component. The CF splitting ground state is a triplet 5. The type-II antiferromagnetic ordering characterized by the propagation vector (1/2, 1/2, 1/2) appears below approximately 4 K. The powder diffraction pattern is reproduced by the ordered magnetic moments aligning along the direction perpendicular to the propagation vector. The magnitude of the ordered magnetic moment is evaluated as 1.36uB/Pr, which is less than 2.0uB/Pr expected from the 5 ground state. Dual electronic states of both localized and itinerant character are inferred.

The metal-nonmetal transition in Ce- and Rh-substituted ${\text{PrRu}}_{4}$${\text{P}}_{12}$ was investigated through magnetic susceptibility, x-ray superlattice reflection, and inelastic neutron scattering (INS) measurements. The saturation in the magnetic susceptibility at low temperatures suggests a singlet ground state for Pr sites in both compounds. This finding is in contrast to the staggered order of singlet and triplet ground states found in the ordered phase of ${\text{PrRu}}_{4}$${\text{P}}_{12}$, which leads to a diverging susceptibility. The intensities of x-ray superlattice reflections of both compounds develop below 45 K and decrease rapidly below 10 K with a simultaneous decrease in electrical resistivity. INS experiments reveal that 4$f$ electron states in both compounds change drastically from two distinct crystal field (CF) level schemes corresponding to an order parameter in the multipole ordered phase (10 $\text{K}lTl45$ K) to a nearly uniform CF level scheme below 10 K. The uniform CF ground state at the Pr sites carries no degree of freedom relevant to the staggered ordering pattern and electronic gap formation. Therefore, the substituted systems exhibit a reentrant metallic state at the lowest temperature. These phenomena may originate from effective electron doping due to atomic substitution.