Neutron scattering measurements on the pyrochlore magnet Ce2Zr2O7 reveal an unusual crystal field splitting of its lowest J = 5/2 multiplet, such that its ground state doublet is composed of mJ = ± 3/2, giving these doublets a dipole -octupole (DO) character with local Ising anisotropy. Its magnetic susceptibility shows weak antiferromagnetic correlations with θCW = -0.4(2) K, leading to a naive expectation of an All-In, All-Out ordered state at low temperatures. Instead our low energy inelastic neutron scattering measurements show a dynamic quantum spin ice state, with suppressed scattering near |Q| = 0, and no long range order at low temperatures. This is consistent with recent theory predicting symmetry enriched U(1) quantum spin liquids for such DO doublets decorating the pyrochlore lattice. Finally, we show that disorder, especially oxidation of powder samples, is important in Ce2Zr2O7 and could play an important role in the low temperature behaviour of this material.The rare-earth pyrochlore oxides R 2 B 2 O 7 , where R 3+ and B 4+ consist generally of rare earth and transitionmetal ions respectively, display a wealth of both exotic and conventional magnetic ground states. Their R 3+ ions decorate a network of corner-sharing tetrahedra, one of the archetypes for geometrical frustration in three dimensions. Due to strong crystal electric field (CEF) effects, the nature of the magnetic interactions in such materials are strongly influenced by their single-ion physics [1][2][3]. A naive theoretical description of the magnetic interactions in rare-earth pyrochlores is generally performed by introducing an ad hoc effective single-ion term in addition to Heisenberg exchange interactions. For example, Heisenberg antiferromagnetism with an effective Ising anisotropy leads to non-frustrated All-In, All-Out (AIAO) magnetic order, as seen in several heavy rare earth iridate pyrochlores [4,5] and illustrated in the insert to Fig.1(a). Heisenberg ferromagnetism and an effective Ising anisotropy give rise to a classical spin ice ground state [6], as seen in (Ho,Dy) 2 Ti 2 O 7 [7, 8] and illustrated as the 2I2O local structure in the inset to Fig.1(a). However, to capture all the physics that can arise at low temperatures, the magnetic interactions should be projected into pseudo-spin operators acting solely on the low energy CEF states [3,[9][10][11][12][13]. This procedure has been applied for example in the Yb 3+ [11,14,15] and Er 3+ [12, 16-18] XY pyrochlores where CEF effects give rise to effective S = 1/2 quantum degrees of freedom that interact via anisotropic exchange interactions.More recently, it has been realized that the precise composition of the ground state crystal field doublets in rare-earth pyrochlores is crucial in determining the form of the microscopic Hamiltonian, and in itself, diversifies the possibility of quantum magnetic states [3,19]. This has been appreciated for some time in the case of non-Kramers doublets, based on magnetic ions with an even number of electrons such as the 4f 2 configuratio...

We present muon spin rotation and relaxation (µSR) measurements as well as demagnetising field corrected magnetisation measurements on polycrystalline samples of the noncentrosymmetric superconductor BeAu. From µSR measurements in a transverse field, we determine that BeAu is a type-I superconductor with Hc = 256 Oe, amending the previous understanding of the compound as a type-II superconductor. To account for demagnetising effects in magnetisation measurements, we produce an ellipsoidal sample, for which a demagnetisation factor can be calculated. After correcting for demagnetising effects, our magnetisation results are in agreement with our µSR measurements. Using both types of measurements we construct a phase diagram from T = 30 mK to Tc ≈ 3.25 K. We then study the effect of hydrostatic pressure and find that 450 MPa decreases Tc by 34 mK, comparable to the change seen in type-I elemental superconductors Sn, In and Ta, suggesting BeAu is far from a quantum critical point accessible by the application of pressure. arXiv:1902.00073v1 [cond-mat.supr-con]

Rare earth garnets are an exciting playground for studying the exotic magnetic properties of the frustrated hyperkagome lattice. Here we present a comprehensive study of the single ion and collective magnetic properties of the garnet Er3Ga5O12. Using inelastic neutron scattering, we find a crystal field ground state doublet for Er 3+ with strong Ising anisotropy along local [100] axes. Magnetic susceptibility and heat capacity measurements provide evidence for long-range magnetic ordering with TN = 0.8 K, and no evidence for residual entropy is found when cooling through the ordering transition. Neutron powder diffraction reveals that the ground state spin configuration corresponds to the six-sublattice, Ising antiferromagnetic state (Γ3) common to many of the rare earth garnets. Our results indicate that Er3Ga5O12 is an excellent model system for studying the complex metamagnetism expected for a multi-axis antiferromagnet.

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We report a chemical substitution-induced ferromagnetic quantum critical point in polycrystalline Ni1−xRhx alloys. Through magnetization and muon spin relaxation measurements, we show that the ferromagnetic ordering temperature is suppressed continuously to zero at xcrit = 0.375 while the magnetic volume fraction remains 100% up to xcrit, pointing to a second order transition. Non-Fermi liquid behavior is observed close to xcrit, where the electronic specific heat C el /T diverges logarithmically, while immediately above xcrit the volume thermal expansion coefficient αV /T and the Grüneisen ratio Γ = αV /C el both diverge logarithmically in the low temperature limit, further indication of a ferromagnetic quantum critical point in Ni1−xRhx.

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We present a detailed magnetic study of the triangular antiferromagnet ErMgGaO4. A point charge calculation under the single ion approximation reveals a crystal field ground state doublet with a strong Ising-like behavior of the Er 3+ moment along the c axis. Magnetic susceptibility and specific heat measurements indicate no presence of magnetic transitions above 0.5 K and no evidence of residual entropy as temperature approaching zero. Zero field (ZF) µSR measurements shows no sign of static uniform or random field and longitudinal field (LF) µSR measurements exhibit persistent spin fluctuations down to our lowest temperature of 25 mK. Our results provide evidence of a quantum spin liquid state in the triangular antiferromagnet ErMgGaO4.A quantum spin liquid (QSL) is a state of matter in which spins are highly entangled and do not show magnetic order down to zero temperature [1]. QSL's are of great current interest both from a fundamental physics point of view and for possible applications in quantum computation [2]. Geometrically frustrated magnets (where competing magnetic interactions cannot be simultaneously satisfied) are excellent candidate materials for QSL behavior since magnetic order is suppressed in them by the frustration [3][4][5]. Such frustration frequently arises from antiferromagnetically coupled spins located on triangle-based lattices (stacked triangular, kagome, pyrochlore), and can lead to a highly degenerate ground state without magnetic order. The previously studied quasi-two dimensional triangular layered material YbMgGaO 4 (with YbFe 2 O 4 -type structure) has been attracting considerable interest as a potential quantum spin liquid candidate [6][7][8][9][10][11][12].YbMgGaO 4 has a Curie-Weiss temperature of ∼ -4 K but shows no sign of long-range order down to 30 mK [6,7,9,10]. Its magnetic specific heat in zero field shows a broad hump at 2.4 K instead of sharp λ-type peak which would be expected for a well-defined second order phase transition. The magnetic excitation spectra appears as a broad continuum in inelastic neutron scattering measurements, which has been taken as an evidence for a QSL state [7,10]. Particularly, the anisotropic exchange interactions between rare earth ions are found to be playing a crucial role in stabilizing such spin liquid ground state [6-10], although an alternative explanantion in terms of the random Ga/Mg site mixing has also been proposed [11]. Such exchange interactions associated with spin orbit coupling strongly depends on rare earth ions. It has also been found, particularly, in rare earth pyrochlores (R 2 B 2 O 7 with R = rare earth, B = non-magnetic cation), that the interplay of exchange couplings, dipolar interactions, and single ion anisotropy leads to spin glasses [5,13], spin liquids [14-16], spin ices [17], order-by-disorder [18, 19], magnetic moment fragmentation [20,21], and conventional long-range magnetic ordering [22]. These observations indicating different rare earth ions can result in much different ground states, motivating the sea...