Relation between paramagnetic entropy and disordered local moment in La(Fe0.88Si0.12)13 magnetocaloric compound

Abstract

The paramagnetic fluctuations are investigated in La(Fe0.88Si0.12)13. The disordered local moment (DLM) is represented by the first principle calculations. With a reduction of the volume, the DLM amplitude decreases gradually. In the temperature dependence of electrical resistivity ρ under hydrostatic pressure, an upturn in the variation of ρ in the paramagnetic state was observed with decreasing temperature, which is originated from the Curie-Weiss-type DLM fluctuations. In the vicinity of the critical pressure for disappearance of the DLM, the variation of ρ as a function of log(T) was observed.

Moment‐Volume Coupling in La(Fe1−xSix)13

“…This may be a consequence of the disordered arrangement, whereas the rhombohedral symmetry constraint present in the 28 atom cell enforces that three Fe II sites flip their direction simultaneously, which is an artificial constraint not present in real disordered compounds. Taking into account the differences in the choice of the simulation cell and the technical setup, these results are consistent, while there is also reasonable agreement with previous calculations of ordered LaFe 12 Si 1 using the full potential localized orbital (FPLO) code and VASP and disordered off‐stoichiometric LaFe 11.5 Si 1.5 obtained with the KKR‐CPA method …”

“…Previous approaches have represented off‐stoichiometric 1:13 phases either by placing Si on the (8b) sites − which is incorrect from the crystallography point of view but retains the symmetry − or use an analytic description of disorder within the virtual crystal or the coherent potential approximation . All of these approaches take full advantage of the high cubic symmetry with three inequivalent lattice sites.…”

“…For the knowledge‐based optimization of these materials, a basic understanding of their intrinsic properties on the electronic scale is of fundamental importance. This includes first‐principles calculations of the electronic structure of ternary and quaternary compositions, Mößbauer spectroscopy for the magnetic properties, structural properties from neutron diffraction and even spin wave stiffness or Debye temperature from measurements of the low temperature specific heat . Thus apart from materials engineering such as optimization of microstructure and thermodynamic properties, large efforts have been dedicated to fundamental research.…”

Electronic structure, metamagnetism and thermopower of LaSiFe12and interstitially doped LaSiFe12

“…There is also mounting evidence that the magnetism of La(Fe,Si) 13 is intermediate between a full itineracy and full localisation. The presence of disordered local moments (DLMs) in the paramagnetic state has been supported by anomalous Hall effect measurements [58], photoemission [59], coherent potential approximation (CPA) calculations [60,61] and recent fixed spin moment calculations [62]. Since the DLM moment may be of the order of 1 µ B , we calculate the fieldinduced change of magnetic entropy as a fixed value, −Rln(2J + 1), where we set J = 0.5 rather than the value of J = 1 that Jia et al used, to reduce the possibility of overestimating the magnetic contribution (since the expression ∆S M = −Rln(2J + 1) yields an overestimate for the true change in magnetic entropy at a finite temperature, first order phase transition, even if the appropriate value of J is used).…”

Moment-volume coupling in La(Fe$_{1-x}$Si$_x$)$_{13}$

“…For the knowledge-based optimization of these materials, a basic understanding of their intrinsic properties on the electronic scale is of fundamental importance. This includes first-principles calculations of the electronic structure of ternary and quaternary compositions [22][23][24][25][26][27][28][29][30], Mössbauer spectroscopy for the magnetic properties [23,31,32], structural properties from neutron diffraction [33,34] and even spin wave stiffness or Debye temperature from measurements of the low temperature specific heat [35]. Thus * Markus.Gruner@uni-due.de apart from materials engineering such as optimization of microstructure and thermodynamic properties, a large amount of efforts has been dedicated to fundamental research.…”