Spin-glass behavior in KxRu4-yNiyO8 hollandite materials

We report the synthesis and comprehensive ac and dc susceptibility measurements of KxRu4−yNiyO8 hollandite. The value of the relative frequency shift, δTf , has been determined as 0.025 which is within the range expected for spin-glass systems (0.005–0.06). Additionally, the characteristic flipping time of a single spin flip, τ0, and the dynamical critical exponent, −zv, were determined to have values of 5.82×10−8 s and 6.1(3), respectively from the power law. While the value of τ0 is comparatively very large, −zv is consistent with what is expected for spin-glass systems. Field-cooled hysteresis behavior demonstrates a small increase in the remnant magnetization (at 2 K) on increasing the strength of the cooling field, suggesting that the degree of short-range correlations increases consistent with the formation of larger spin clusters. Thermoremnant magnetization data indicate an exponential-like decay of the magnetization as a function of time with the remnant magnetization remaining nonzero. However, it is clear from these data that multiple components contribute to the decay behavior. Collectively, these data confirm spin-glass character for K0.73(3)Ni1.9(5)Ru2.1(5)O8 and clearly demonstrate that the magnetic behavior of this material is far from simplistic

The magnetic structure and field dependence of the cycloid phas mediating the spin reorientation transition in Ca₃Ru₂O₇

We report a comprehensive experimental investigation of the magnetic structure of the cycloidal phase in Ca3Ru2O7, which mediates the spin reorientation transition, and establishes its magnetic phase diagram. In zero applied field, single-crystal neutron diffraction data confirms the scenario deduced from an earlier resonant x-ray scattering study: between 46.7~K <T<49.0~K the magnetic moments form a cycloid in the a−b plane with a propagation wavevector of (δ,0,1) with δ≃0.025 and an ordered moment of about 1 μB, with the eccentricity of the cycloid evolving with temperature. In an applied magnetic field applied parallel to the b-axis, the intensity of the (δ,0,1) satellite peaks decreases continuously up to about μ0H≃5 T, above which field the system becomes field polarised. Both the eccentricity of the cycloid and the wavevector increase with field, the latter suggesting an enhancement of the anti−symmetric Dzyaloshinskii−Moriya interaction via magnetostriction effects. Transitions between the various low-temperature magnetic phases have been carefully mapped out using magnetometry and resistivity. The resulting phase diagram reveals that the cycloid phase exists in a temperature window that expands rapidly with increasing field, before transitioning to a polarised paramagnetic state at 5 T. High-field magnetoresistance measurements show that below T≃70 K the resistivity increases continuously with decreasing temperature, indicating the inherent insulating nature at low temperatures of our high-quality, untwinned, single-crystals. We discuss our results with reference to previous reports of the magnetic phase diagram of Ca3Ru2O7 that utilised samples which were more metallic and/or poly-domain

Magnetic structure and field dependence of the cycloid phase mediating the spin reorientation transition in Ca3Ru2 O7

We report a comprehensive experimental investigation of the magnetic structure of the cycloidal phase in Ca3Ru2O7, which mediates the spin reorientation transition and establishes its magnetic phase diagram. In zero applied field, single-crystal neutron diffraction data confirm the scenario deduced from an earlier resonant x-ray scattering study: For 46.7K <T< 49.0 K the magnetic moments form a cycloid in the a-b plane with a propagation wave vector of (δ,0,1) with δ≃0.025 and an ordered moment of about 1μB, with the eccentricity of the cycloid evolving with temperature. In an applied magnetic field applied parallel to the b axis, the intensity of the (δ,0,1) satellite peaks decreases continuously up to about μ0H≃5T, above which field the system becomes field polarized. Both the eccentricity of the cycloid and the wave vector increase with field, the latter suggesting an enhancement of the antisymmetric Dzyaloshinskii-Moriya interaction over the symmetric exchange interactions via magnetostriction effects. Transitions between the various low-temperature magnetic phases have been carefully mapped out using magnetometry and resistivity. The resulting phase diagram reveals that the cycloid phase exists in a temperature window that expands rapidly with increasing field, before transitioning to a polarized paramagnetic state at 5 T. High-field magnetoresistance measurements show that below T≃70K the resistivity increases continuously with decreasing temperature, indicating the inherent insulating nature at low temperatures of our high-quality, untwinned, single crystals. We discuss our results with reference to previous reports of the magnetic phase diagram of Ca3Ru2O7 that utilized samples which were more metallic and/or polydomain

Non-volatile voltage-controlled magnetization in single-phase multiferroic ceramics at room temperature

Single-phase multiferroics (MFs) exhibiting ferroelectricity and ferromagnetism and the strong magnetoelectric (ME) coupling effect at room temperature are seen as key to the development of the next-generation of spintronic devices, multi-state memories, logic devices and sensors. Herein, the single-tetragonal phase (1–x) (Sr0·3Bi0·35Na0·329Li0.021)TiO3-xBiFeO3 (x = 0.2 or 0.4) system was designed to study the intrinsic ME coupling effect at room temperature and high frequencies. The polarization arises from the cooperative displacement of both Fe3+ and Ti4+ relative to the oxygen sublattice in the tetragonally distorted perovskite structure, and the magnetization stems from indirect exchange magnetic interaction between adjacent iron ions. A switchable voltage-controlled magnetization was confirmed by a change of the coercive magnetic field, Hc, and remnant magnetization, Mr, in the x = 0.4 component subjected to an external electric field at room temperature and was possibly attributed to a strain-mediated ME coupling effect. In addition, resonance behaviours of the complex magnetic permeability and complex dielectric permittivity in the GHz band indicate that this ME effect is intrinsic in nature and could broaden the applications of multiferroics to devices operating at microwave frequencies

Quantum critical spin-liquid-like behavior in S = 1/2 quasi-kagome lattice compound CeRh₁-ₓPdₓSn investigated using muon spin relaxation and neutron scattering

We present the results of muon spin relaxation (μSR) and neutron scattering on the Ce-based quasikagome lattice CeRh1−xPdxSn (x=0.1 to 0.75). Our ZF-μSR results reveal the absence of static long-range magnetic order down to 0.05~K in x=0.1 single crystals. The weak temperature-dependent plateaus of the dynamic spin fluctuations below 0.2~K in ZF-μSR together with its longitudinal-field (LF) dependence between 0 and 3~kG indicate the presence of dynamic spin fluctuations persisting even at T = 0.05~K without static magnetic order. On the other hand, C4f/T increases as --log T on cooling below 0.9~K, passes through a broad maximum at 0.13~K and slightly decreases on further cooling. The ac-susceptibility also exhibits a frequency independent broad peak at 0.16~K, which is prominent with an applied field H along c-direction. We, therefore, argue that such a behavior for x=0.1 (namely, a plateau in spin relaxation rate (λ) below 0.2~K and a linear T dependence in C4f below 0.13~K) can be attributed to a metallic spin-liquid (SL) ground state near the quantum critical point in the frustrated Kondo lattice. The LF-μSR study suggests that the out of kagome plane spin fluctuations are responsible for the SL behavior. Low energy inelastic neutron scattering (INS) of x = 0.1 reveals gapless magnetic excitations, which are also supported by the behavior of C4f proportional to T1.1 down to 0.06~K