Heavy-fermion systems studied by μSR technique

Abstract

The author attempts to give a comprehensive discussion of studies performed with the positive-muon spin rotation and relaxation technique (also known as the SR technique) on heavy-fermion compounds. The subtle competition between the demagnetizing Kondo interaction and the intersite Ruderman-Kittel-Kasuya-Yosida exchange interaction is believed to be the primary ingredient for the wealth of different ground states observed for this class of rare-earth-and actinide-containing intermetallic compounds. Due to its microscopic character, its sensitivity to extremely small internal fields, and its capacity to detect spatially inhomogeneous magnetic features, the SR technique has been extensively utilized to investigate the peculiar magnetic properties of these ground states and improve our knowledge of heavy-fermion phenomena. In addition to providing a short introduction to SR, where the intrinsic difficulties of the method are clearly stated, this article reviews the main results obtained by this technique on the best-known heavy-fermion compounds (superconductors, band magnets, local-moment magnets, non-Fermi-liquid systems, and Kondo insulators). Special emphasis is placed on the particular information obtainable by monitoring the implanted muon. [S0034-6861(97)00104-9] CONTENTS I. Introduction 1119 A. Puzzle of heavy-fermion physics 1119 B. Tentative classification of heavy-fermion systems 1120 C. Advantages of the SR technique in studying heavy-fermion compounds 1122 D. Organization of the review 1123 II. Overview of the SR Technique 1123 A. Muon production 1124 B. Principle of SR 1124 C. The SR transverse-field (TF) technique

Magnetism and superconductivity in underscreened Kondo chains

“…Thus it came as a surprise when it was discovered in 1984 by Schlabitz et al [1] that magnetism and superconductivity actually coexisted in the heavy fermion compound URu 2 Si 2 . Since then, other heavy fermion superconductors were shown to present magnetic moments in their superconducting phase [2]. All these compounds contain rare earth or actinide ions with very localized 4f or 5f orbitals, strongly interacting with the conduction band.…”

Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

“…Among these, Ce-based compounds are well known for exhibiting a wide range of physical properties such as long range magnetic ordering with different ground states, Kondo lattice behavior, heavy fermion behavior, valance fluctuation, superconductivity and quantum criticality which arise from the competition between the RKKY and the Kondo interactions. [1][2][3][4][5][6] The family of CeT 2 X 2 (T= transition element, X = Ge, Si) compounds have been intensively studied because of their interesting magnetic and superconducting properties. [7][8][9][10][11][12] For example, Kondo lattice antiferromagnet CeCu 2 Si 2 is a heavy fermion superconductor that exhibits the coexistence of magnetism and superconductivity.…”

First-order nature of the ferromagnetism in CeIn2investigated using muon spin rotation and by systematic substitution of La for Ce

“…The frequencies are proportional to the local field (2πν = γ μ H loc ) at the muon site, therefore the related values of H loc change from 1.9 kOe at 22 K to 3.1 kOe at 10 K for ν 1 , and from 0.7 to 1.08 kOe for ν 2 , respectively. These values of the internal field H loc , especially those related to ν 1 , are relatively large when compared with those reported for other Ce, Yb, and U compounds, 11 and even larger than those of MnSi, 13 also with a first-order ferromagnetic transition. This may indicate a high degree of localization of 4f moments in CeIn 2 , although H loc does not only depend on the ordered moment, but also on the particularities of the crystallographic structure.…”

“…3) show a fast depolarized signal at low times in CeIn 2 , with a broad distribution of static local fields at the muon site, characteristic of incommensurate magnetic structures. 11,14,16 In fact, the chemical substitution of Ce by La reveals an additional contribution at T * , above T C , in the ac-magnetic susceptibility and specific heat for the samples with a Ce concentration of x = 0.9 and x = 0.95. Furthermore, these results indicate that the magnetic transition taking place at T * is closer to T C in CeIn 2 than in the La-diluted alloys with x = 0.9 and x = 0.95, and thus it might be masked by the short-range magnetic correlations established above T C , as can be concluded from Fig.…”

“…11 Very recently, this technique successfully proved the first-order ferromagnetic transition of the itinerant helimagnet MnSi. 12 Due to its microscopic character and sensitivity to extremely small internal fields, it can reveal spatially inhomogeneous magnetic features associated with the influence of the crystalline environment on the muon spin motion.…”