Jamming in Spin Systems

Abstract

Dedicated to my family and all my teachers.i "The true sign of intelligence is not knowledge but imagination." Albert Einsteinii Abstract Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for the existence of a glassy state, that we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which shows unconventional spin glass properties, such as the quadratic low-temperature dependence of heatcapacity, a broad elastic neutron scattering peak centred around a non-zero wavevector ( ), and insensitivity to low-concentration of defects. We have mainly studied two isostructural frustrated magnets, SrCr9pGa12-9pO19 (SCGO(p)) and BaCr9pGa12-9pO19 (BCGO(p)), in which the magnetic Cr 3+ (s=3/2) ions form a quasi-two-dimensional (Q2D) triangular system of bi-pyramids, in comparison to several other magnetic glasses ranging from dilute magnetic alloys to threedimensional frustrated magnets.We performed both bulk susceptibility and neutron scattering experiments on both SCGO(p) and BCGO(p) systems as a function of dilution p in the range of 0.4 ≲ p ≲0.97. Our bulk susceptibility data exhibit glassy behavior at much lower temperatures ( ) than the absolute values of the Curie-Weiss temperature, | | ≈ -504(2) K for SCGO(p = 0.968(6)) and -695(1) K for BCGO(p = 0.902(8)). The frustration index = | |/ is as high as 130 for SCGO(p = 0.968(6)) and 190for BCGO(p = 0.902(8)) indicating strong frustration. Low-temperature susceptibility measurements of SCGO(p)/BCGO(p) reveals glass-like signatures such as zero-field cooled (ZFC) -field cooled (FC) hysteresis and frequency dependent AC susceptibility but the low-temperature magnetic phases found in the dense limit of magnetic ions show distinct properties from conventional spin glasses.Our inelastic neutron scattering data on SCGO(p = 0.968(6)) and BCGO(p = 0.902(8)) shows dispersionless magnetic excitations centered at ℏω = 18.6(1) meV and 16.5(1) meV respectively, due to singlet to triplet excitations of spin s = 3/2 dimers. The spin dimers are formed by Cr 3+ ions in two 4fvi layers that lie between 12k-2a-12k (kagome-triangle-kagome) trilayers. Moreover, a iii continuum spectrum centered around ≈ 1.5 Å , observed in time-of-flight (TOF) neutron scattering experiments for SCGO(p)/BCGO(p) magnets, confirm that the kagome−triangular−kagome trilayer is responsible for low-energy spin dynamics. The imaginary part of dynamical susceptibility ( ( )) for SCGO(p = 0.968(6)) or BCGO(p = 0.902 (8)) shows linear dependence at low-energies which is inconsistent with energy independent behavior of di...

Effect of aqueous extracts of the sprouted seeds on the quantitative and qualitative yield of the coral lettuce cultured under the modified nutrient solution film NFT system

“…The production of vegetables by hydroponics is increasing rapidly with the increased interest in consuming high-quality, fresh local foods throughout the year. Among the various hydroponic systems, producing leafy green vegetables using NFT is the most common practice in this system 1,2 , where the nutrient solution is continuously cycled to replenish nutrients and oxygen dissolved during the production cycle.…”