Neutron diffraction and inelastic spectroscopy is used to characterize the magnetic Hamiltonian of SrHo 2 O 4 and SrDy 2 O 4 . Through a detailed computation of the crystal-field levels we find site-dependent anisotropic single-ion magnetism in both materials, and diffraction measurements show the presence of strong one-dimensional spin correlations. Our measurements indicate that competing interactions of the zigzag chain, combined with frustrated interchain interactions, play a crucial role in stabilizing spin-liquid type correlations in this series.

Magnetic frustration and low dimensionality can prevent long range magnetic order and lead to exotic correlated ground states. SrDy 2 O 4 consists of magnetic Dy 3+ ions forming magnetically frustrated zig-zag chains along the c-axis and shows no long range order to temperatures as low as T = 60 mK. We carried out neutron scattering and AC magnetic susceptibility measurements using powder and single crystals of SrDy 2 O 4 . Diffuse neutron scattering indicates strong one-dimensional (1D) magnetic correlations along the chain direction that can be qualitatively accounted for by the axial next-nearest neighbour Ising (ANNNI) model with nearestneighbor and next-nearest-neighbor exchange J 1 = 0.3 meV and J 2 = 0.2 meV, respectively. Three-dimensional (3D) correlations become important below T * ≈ 0.7 K. At T = 60 mK, the short range correlations are characterized by a putative propagation vector k 1/2 = (0,2 ). We argue that the absence of long range order arises from the presence of slowly decaying 1D domain walls that are trapped due to 3D correlations. This stabilizes a low-temperature phase without long range magnetic order, but with well-ordered chain segments separated by slowly-moving domain walls.

We report on muon spin rotation studies of the noncentrosymmetric heavy fermion antiferromagnet CeRhSi3. A drastic and monotonic suppression of the internal fields, at the lowest measured temperature, was observed upon an increase of external pressure. Our data suggest that the ordered moments are gradually quenched with increasing pressure, in a manner different from the pressure dependence of the Néel temperature. At 23.6 kbar, the ordered magnetic moments are fully suppressed via a second-order phase transition, and TN is zero. Thus, we directly observed the quantum critical point at 23.6 kbar hidden inside the superconducting phase of CeRhSi3. PACS numbers: 76.75.+i, 75.50.Ee, 75.30.Mb, 75.40.Cx The role of magnetism in many superconducting materials is a topic of intense research. Often, these materials display a quantum critical point (QCP) that separates a nonmagnetic from a magnetic metallic phase [1][2][3]. This usually leads to the formation of new phases of matter, whose properties are dominated by quantum fluctuations. These fluctuations can be fine-tuned by an external parameter, such as chemical substitution, magnetic field or external pressure. The location and nature of QCPs are central to the understanding of the interplay between superconductivity and magnetism in these systems. In a number of heavy fermion compounds such as CePd 2 Si 2 , CeIn 3 , and CeIrSi 3 , the QCP is buried deep inside of a superconducting phase in the pressuretemperature phase diagram [2,4,5]. In these cases, it is challenging to establish the presence of a QCP and to study the microscopic magnetic properties coexisting with superconductivity. In this muon spin rotation (µSR) study on the heavy fermion CeRhSi 3 , we uncovered the previously conjectured QCP hidden inside the superconducting phase. We directly observed the disappearance of the ordered magnetic moments at the critical pressure p * = 23.6 kbar deep inside the superconducting phase. This suppression of the ordered moments was found to be accompanied by a zeroing of the Néel temperature at p * suggesting that this QCP is of magnetic nature.CeRhSi 3 is a noncentrosymmetric heavy fermion system [6][7][8], suspected to display a QCP [6, 9, 10] at pressures of the order of 26 kbar. The compound features an intriguing phase diagram. It displays an AFM phase at ambient and applied pressure and a superconducting phase for pressures p > 12 kbar [6,11]. Measurements of the de Haas-van Alphen effect at ambient and applied pressure show that the f electrons are itinerant up to at least 30 kbar [9]. Neutron diffraction at ambient pressure showed that the magnetic order is incommensurate, with ordered moments of the order of 0.1 µ B /Ce [12]. From previous results of thermal and transport properties, it was established that the antiferromagnetic ordering temperature T N ≈ 1.6 K at ambient pressure initially increases with increasing pressure and then decreases towards the superconducting transition temperature T c ∼ 1 K for p ≈ 20 kbar. The nature of the magnetism above...