Crystal electric field next to a hydrogen-like interstitial— µ+ in PrNi5

On the Robustness of the MnSi Magnetic Structure Determined by Muon Spin Rotation

Muon spin rotation ( μ SR) spectra recorded for manganese silicide MnSi and interpreted in terms of a quantitative analysis constrained by symmetry arguments were recently published. The magnetic structures of MnSi in zero-field at low temperature and in the conical phase near the magnetic phase transition were shown to substantially deviate from the expected helical and conical structures. Here, we present material backing the previous results obtained in zero-field. First, from simulations of the field distributions experienced by the muons as a function of relevant parameters, we confirm the uniqueness of the initial interpretation and illustrate the remarkable complementarity of neutron scattering and μ SR for the MnSi magnetic structure determination. Second, we present the result of a μ SR experiment performed on MnSi crystallites grown in a Zn-flux and compare it with the previous data recorded with a crystal obtained from Czochralski pulling. We find the magnetic structure for the two types of crystals to be identical within experimental uncertainties. We finally address the question of a possible muon-induced effect by presenting transverse field μ SR spectra recorded in a wide range of temperature and field intensity. The field distribution parameters perfectly scale with the macroscopic magnetization, ruling out a muon-induced effect.

Anisotropic local modification of crystal field levels in Pr-based pyrochlores: a muon-induced effect modeled using density functional theory

Although muon spin relaxation is commonly used to probe local magnetic order, spin freezing, and spin dynamics, we identify an experimental situation in which the measured response is dominated by an effect resulting from the muon-induced local distortion rather than the intrinsic behavior of the host compound. We demonstrate this effect in some quantum spin ice candidate materials Pr(2)B(2)O(7) (B=Sn, Zr, Hf), where we detect a static distribution of magnetic moments that appears to grow on cooling. Using density functional theory we show how this effect can be explained via a hyperfine enhancement arising from a splitting of the non-Kramers doublet ground states on Pr ions close to the muon, which itself causes a highly anisotropic distortion field. We provide a quantitative relationship between this effect and the measured temperature dependence of the muon relaxation and discuss the relevance of these observations to muon experiments in other magnetic materials.

Investigations of the singlet ground state system: PrIrSi3

We report our comprehensive study of physical properties of a ternary intermetallic compound PrIrSi3 investigated by dc magnetic susceptibility χ(T), isothermal magnetization M(H), thermo-remnant magnetization M(t), ac magnetic susceptibility χac(T), specific heat Cp(T), electrical resistivity ρ(T), muon spin relaxation (µSR) and inelastic neutron scattering (INS) measurements. A magnetic phase transition is marked by a sharp anomaly at Ttr = 12.2 K in χ(T) measured at low applied fields which is also reflected in the Cp(T) data through a weak anomaly at 12 K. An irreversibility between the zero field cooled and field cooled χ(T) data below 12.2 K and a very large relaxation time of M(t) indicates the presence of ferromagnetic correlation. The magnetic part of specific heat shows a broad Schottky-type anomaly near 40 K due to the crystal electric field (CEF) effect. An extremely small value of magnetic entropy below 12 K suggests a CEF-split singlet ground state which is confirmed from our analysis of INS data. The INS spectra show two prominent inelastic excitations at 8.5 meV and 18.5 meV that could be well accounted by a CEF model. The CEF splitting energy between the ground state singlet and the first excited doublet is found to be 92 K. Our µSR data reveal a possible magnetic ordering below 30 K, which is much higher than that found from the specific heat and magnetic susceptibility measurements. This could be due to the presence of short range correlations well above the long range magnetic ordering or due to the electronic changes induced by muons. The induced moment magnetism in the singlet ground state system PrIrSi3 with such a large splitting energy of 92 K is quite surprising.

Ground state of the easy-axis rare-earth kagome langasite Pr3Ga5SiO14

We report muon spin relaxation and {69,71}Ga nuclear quadrupolar resonance local-probe investigations of the kagome compound Pr3Ga5SiO14. Small quasistatic random internal fields develop below 40 K and persist down to our base temperature of 21 mK. They originate from hyperfine-enhanced 141Pr nuclear magnetism which requires a nonmagnetic Pr3+ crystal-field (CF) ground state. In addition, we observe a broad maximum of the relaxation rate at approximately 10 K which we attribute to the population of the first excited magnetic CF level. Our results yield a Van Vleck paramagnet picture, at variance with the formerly proposed spin-liquid ground state.

Quantized hyperfine field at an implanted micro+ site in PrPb3: interplay between localized f electrons and an interstitial charged particle

The local effect of an interstitial hydrogenlike particle on localized f electrons was studied in PrPb3 by means of micro+ spin rotation and relaxation. Spontaneous micro+ spin precession with harmonic frequencies was observed for the first time in f electron compounds. We demonstrate that the signal is derived from a coupling between the micro+ spin and the hyperfine-enhanced nuclear spin of nearest neighbor (NN) 141Pr with Ising-like anisotropy. The signal also suggests a marked suppression of spin dynamics of the NN 141Pr in comparison with that of the bulk 141Pr. These facts strongly indicate modification of the f electronic state due to the interstitial charged particle.

Temperature and field dependence of the order parameter in the antiferroquadrupolar phase of CeB6 from mu+ Knight shift measurements

The Fermi contact hyperfine contribution to the Knight shift of positive muons, implanted at the interstitial 3d sites in CeB6, is found to exhibit the same temperature dependence below T(Q) in phase II as the quadrupolar order parameter determined from resonant and nonresonant x-ray scattering. Furthermore, the contact coupling parameter is shown to be anisotropic and field dependent. These unanticipated features are interpreted to arise from the RKKY induced conduction electron spin polarization, which depends on the orientation and expectation value of the ordered 4f quadrupole moments.