5 research outputs found
Magnetoelectric correlations in BiMnO whithin Landau theory: comparison with experiment
We discuss a simple phenomenological Landau theory of phase transitions with
two coupled single-component order parameters and compare the results with
available experimental data. The model corresponds to the case of a ferroic
system, in which ferromagnetic and ferroelectric transitions originally occur
at temperatures and , respectively. For the
magnetoelectric coupling strongly renormalizes the magnetic transition
temperature, (with ), as well as generates an
additional anomaly in ferroelectric subsystem . Full susceptibility
tensor has also been determined. The concept of \textit{Arrot plot} is replaced
by the \textit{Arrot planes} which appear when both types of order coexist. The
results are in good overall agreement with experimental data for the
ferroelectromagnetic BiMnO. We also estimate the contribution of Gaussian
fluctuations of both order parameters, that lead to corrections to the
mean-field specific heat. Those corrections are still insufficient even though
other quantities agree quite well with experiment. We calculate the temperature
dependence of the coherence length for both types of order as well.Comment: 27 pages, 12 figure
Anderson lattice with explicit Kondo coupling: general features and the field-induced suppression of heavy-fermion state in ferromagnetic phase
We apply the extended (statistically-consistent, SGA) Gutzwiller-type
approach to the periodic Anderson model (PAM) in an applied magnetic field and
in the strong correlation limit. The finite-U corrections are included
systematically by transforming PAM into the form with Kondo-type interaction
and residual hybridization, appearing both at the same time. This effective
Hamiltonian represents the essence of \textit{Anderson-Kondo lattice model}. We
show that in ferromagnetic phases the low-energy single-particle states are
strongly affected by the presence of the applied magnetic field. We also find
that for large values of hybridization strength the system enters the so-called
\textit{locked heavy fermion state}. In this state the chemical potential lies
in the majority-spin hybridization gap and as a consequence, the system
evolution is insensitive to further increase of the applied field. However, for
a sufficiently strong magnetic field, the system transforms from the locked
state to the fully spin-polarized phase. This is accompanied by a metamagnetic
transition, as well as by drastic reduction of the effective mass of
quasiparticles. In particular, we observe a reduction of effective mass
enhancement in the majority-spin subband by as much as 20% in the fully
polarized state. The findings are consistent with experimental results for
CeLaB compounds. The mass enhancement for the spin-minority
electrons may also diminish with the increasing field, unlike for the
quasiparticles states in a single narrow band in the same limit of strong
correlations
Spin and magnetic field dependences of quasiparticle mass in ferromagnetic state of heavy fermions
We investigate the mechanism underlying the suppression of heavy-fermion mass enhancement in the presence of a magnetic field. In the framework of statistically consistent Gutzwiller method (SGA) we study the periodic Anderson model in the strong correlation limit. The finite-U corrections are included systematically allowing to describe the coexistence of Kondo compensation effect and ferromagnetic ordering, as well as weak delocalization of the f-electrons. In particular, we observe that the resulting mass enhancement factor of spin-up electrons and that of spin-down are not equal in ferromagnetic phases and depend strongly on the applied field and the f-level occupancy. We predict that mass enhancement for the spin-up quasiparticles is larger then that of spin-down and both of them decrease in the applied magnetic field. We argue that above features, as well as a nonmonotonic variation of the quasiparticle effective masses observed in our model are in good agreement with earlier experimental measurements for Ce_{x}La_{1− x}B_{6}