It is now well established that the paramagnetic to ferromagnetic transition in the magnetocaloric La(FeSi)13 is a cooperative effect involving spin, charge and lattice degrees of freedom. However, the influence of this correlated behaviour on the ferromagnetic state is as yet little studied. Here we measure the specific heat at low temperatures in a systematic set of LaFexMnySiz samples with and without hydrogen, to extract the Sommerfeld coefficient, the Debye temperature and the spin wave stiffness. Substantial and systematic changes in magnitude of the Sommerfeld coefficient are observed with Mn substitution and introduction of hydrogen, showing that over and above the changes to the density of states at the Fermi energy there are significant enhanced d band electronic interactions, at play. The Sommerfeld coefficient is found to be 90-210 mJmol -1 K -2 unusually high compared to that expected from band structure calculations. The Debye temperature determined from the specific heat measurement is insensitive to Mn and Si doping, but increases when hydrogen is introduced into the system. The Sommerfeld coefficient is reduced in magnetic field for all compositions that have a measurable spin wave contribution. These results move our understanding of the cooperative effects forward in this important and interesting class of materials significantly, and provides a basis for future theoretical development.

High performance quantum information processing requires efficient control of undesired decohering effects, which are present in realistic quantum dynamics. To deal with this issue, a powerful strategy is to employ transitionless quantum driving (TQD), where additional fields are added to speed up the evolution of the quantum system, achieving a desired state in a short time in comparison with the natural decoherence time scales. In this paper, we provide an experimental investigation of the performance of a generalized approach for TQD to implement shortcuts to adiabaticity in nuclear magnetic resonance (NMR). As a first discussion, we consider a single nuclear spin-1 2 system in a time-dependent rotating magnetic field. While the adiabatic dynamics is violated at a resonance situation, the TQD Hamiltonian is shown to be robust against resonance, allowing us to mimic the adiabatic behavior in a fast evolution even under the resonant configurations of the original (adiabatic) Hamiltonian. Moreover, we show that the generalized TQD theory requires less energy resources, with the strength of the magnetic field less than that required by standard TQD. As a second discussion, we analyze the experimental implementation of shortcuts to single-qubit adiabatic gates. By adopting generalized TQD, we can provide feasible time-independent driving Hamiltonians, which are optimized in terms of the number of pulses used to implement the quantum dynamics. The robustness of adiabatic and generalized TQD evolutions against typical decoherence processes in NMR is also analyzed.

A new binuclear copper(ii) complex, namely [Cu2L(pz)(DMSO)], where L = 2,6-bis[(2-phenoxy)iminomethyl]-4-methylthiophenolate(3-) and pz = pyrazolate ligand, has been synthesized by a one-pot synthesis involving copper(ii) acetate monohydrate, the S-protected ligand precursor 2-(N,N-dimethylthiocarbamato)-5-methylisophthalaldehyde di-2'-hydroxy anil, (), and pyrazole, in which a metal-promoted S-deprotection reaction occurs during the formation of the complex. This was characterized by routine physicochemical studies, single crystal X-ray diffraction and electron paramagnetic resonance (EPR) techniques. The structure analysis reveals that there are copper centres in two different environments, a slightly distorted square planar and a distorted square-pyramidal, arranged in binuclear units. The EPR study of these binuclear units performed at 9.4 GHz in the temperature range between 4 and 293 K shows an antiferromagnetic interaction between Cu(II) ions, and allows evaluating g factors gx = 2.068(1), gy = 2.091(1) and gz = 2.165(1), with = 2.108(1), an exchange coupling parameter J0 = -26(1) cm(-1) (defined as ), and a zero field splitting of the ground triplet state described by D = 86(2) × 10(-4) cm(-1) and E = -48(3) × 10(-4) cm(-1). These results are discussed and compared with the existing literature.