Spin glass and ferromagnetism in Kondo lattice compounds (original) (raw)
Related papers
Journal of Magnetism and Magnetic Materials, 2013
The present work studies the effects of a random magnetic field on the competition among Kondo effect, spin glass (SG) phase and ferromagnetic (FE) order in disordered cerium systems such as CeNi 1Àx Cu x. A Kondo lattice model is used with an intersite disordered interaction J ij between localized canonical ones [2-6]. Particularly, the competition between Kondo effect, SG-type state and FE has been investigated using distinct types of random exchange interactions as, for example, the Sherrington-Kirkpatrick (SK) model [2,3], the van Hemmen model [6] and the generalized Mattis model [4]. Nevertheless, the disorder in these studies has been introduced only in the random exchange interaction between the localized f-spins.
Phase diagram of the CeNi1-xCux Kondo system with spin-glass-like behavior favored by hybridization
Physical Review B, 2000
We present the magnetic phase diagram of the Kondo ͑ferromagnetic and antiferromagnetic͒ CeNi 1Ϫx Cu x series revealing the existence of a ''spin-glass-like'' state above the Curie temperature T C. The stability temperature range of this magnetically disordered phase increases when approaching the magnetic localizeddelocalized crossover point (xϷ0.1). This phenomenology is first discussed considering a classical model of spin-glass phase diagram including the effect of Kondo interactions. The similarities to the scenario described by recent theoretical analysis of strongly correlated electron systems, considering disorder and competing Ruderman-Kittel-Kasuya-Yosida and Kondo interactions, are also pointed out.
Spin-glass transition in a Kondo lattice with quenched disorder
Journal of Experimental and Theoretical Physics Letters, 2000
We use the Popov-Fedotov representation of spin operators to construct an effective action for a Kondo lattice model with quenched disorder at finite temperatures. We study the competition between the Kondo effect and frozen spin order in Ising-like spin glass. We present the derivation of new mean-field equations for the spin-glass order parameter and analyze the effects of screening of localized spins by conduction electrons on the spin-glass phase transition.
Intersite Coupling Effects in a Kondo Lattice
Physical Review Letters, 2002
The La dilution of the Kondo lattice CeCoIn5 is studied. The scaling laws found for the magnetic susceptibility and the specific heat reveal two well-separated energy scales, corresponding to the single impurity Kondo temperature TK and an intersite spin-liquid temperature T * . The Ce-dilute alloy has the expected Fermi liquid ground state, while the specific heat and resistivity in the dense Kondo regime exhibit non-Fermi-liquid behavior, which scales with T * . These observations indicate that the screening of the magnetic moments in the lattice involves antiferromagnetic intersite correlations with a larger energy scale in comparison with the Kondo impurity case.
Spin dynamics in the diluted ferromagnetic Kondo lattice model
Journal of Physics: Condensed Matter, 2007
The interplay of disorder and competing interactions is investigated in the carrier-induced ferromagnetic state of the Kondo lattice model within a numerical finite-size study in which disorder is treated exactly. Competition between impurity spin couplings, stability of the ferromagnetic state, and magnetic transition temperature are quantitatively investigated in terms of magnon properties for different models including dilution, disorder, and weakly-coupled spins. A strong optimization is obtained for Tc at hole doping p << x, highlighting the importance of compensation in diluted magnetic semiconductors. The estimated Tc is in good agreement with experimental results for Ga1−xMnxAs for corresponding impurity concentration, hole bandwidth, and compensation. Finite-temperature spin dynamics is quantitatively studied within a locally self-consistent magnon renormalization scheme, which yields a substantial enhancement in Tc due to spin clustering, and highlights the nearly-paramagnetic spin dynamics of weakly-coupled spins. The large enhancement in density of low-energy magnetic excitations due to disorder and competing interactions results in a strong thermal decay of magnetization, which fits well with the Bloch form M0(1 − BT 3/2) at low temperature, with B of same order of magnitude as obtained in recent squid magnetization measurements on Ga1−xMnxAs samples.
Charge and spin inhomogeneous phases in the ferromagnetic Kondo lattice model
Physical Review B, 2002
We study numerically the one-dimensional ferromagnetic Kondo lattice. This model is widely used to describe nickel and manganese perovskites. Due to the competition between double and super-exchange, we find a region where the formation of magnetic polarons induces a charge-ordered state. This ordering is present even in the absence of any inter-site Coulomb repulsion. There is an insulating gap associated to the charge structure formation. We also study the insulator-metal transition induced by a magnetic field which removes simultaneously both charge and spin ordering.
Scaling theory of magnetic ordering in the Kondo lattices with anisotropic exchange interactions
Physical Review B, 1999
The lowest-order scaling consideration of the magnetic state formation in the Kondo lattices is performed within the s−f model with inclusion of anisotropy for both the f − f coupling and s − f exchange interaction. The Kondo renormalizations of the effective transverse and longitudinal s − f coupling parameters, spin-wave frequency, gap in the magnon spectrum and ordered moment are calculated in the case of both ferro-and antiferromagnets. The anisotropy-driven change of the scaling behavior (e.g., critical value of g for entering the strong-coupling region and the corresponding critical exponents) is investigated numerically for N = 2 and analytically in the large-N limit. The dependence of the effective Kondo temperature on the bare s−f coupling parameter g weakens in the presence of anisotropy. The relative anisotropy parameters for both the s − f and f − f coupling are demonstrated to decrease during the renormalization process. The role of next-nearest exchange interactions for this effect in the antiferromagnet is discussed.
Magnetic moment screening in the correlated Kondo lattice model
Journal of the Korean Physical Society, 2013
The magnetic correlations, local moments and the susceptibility in the correlated 2D Kondo lattice model at half filling are investigated. We calculate their systematic dependence on the control parameters J K /t and U/t. An unbiased and reliable exact diagonalization (ED) approach for ground state properties as well as the finite temperature Lanczos method (FTLM) for specific heat and the uniform susceptibility are employed for small tiles on the square lattice. They lead to two major results: Firstly we show that the screened local moment exhibits non-monotonic behavior as a function of U for weak Kondo coupling J K. Secondly the temperature dependence of the susceptibility obtained from FTLM allows to extract the dependence of the characteristic Kondo temperature scale T * on the correlation strength U. A monotonic increase of T * for small U is found resolving the ambiguity from earlier investigations. In the large U limit the model is equivalent to the 2D Kondo necklace model with two types of localized spins. In this limit the numerical results can be compared to those of the analytical bond operator method in mean field treatment and excellent agreement for the total paramagnetic moment is found, supporting the reliability of both methods.
Anisotropic Magnetic Response in Kondo Lattice with Antiferromagnetic Order
Journal of the Physical Society of Japan, 2014
Magnetic properties are investigated for the Kondo lattice by using the continuous time quantum Monte Carlo (CT-QMC) and the dynamical mean field theory (DMFT). The DMFT+CT-QMC approach is extended so as to derive the anisotropic magnetic response in the antiferromagnetic phase. The longitudinal and transverse magnetic susceptibilities are numerically calculated in the antiferromagnetic phase. For the RKKY regime with a small Kondo coupling, the transverse susceptibility does not decrease below the transition temperature while the longitudinal susceptibility decreases as expected from the mean field picture. In the competing region between the RKKY interaction and the Kondo effect, however, both longitudinal and transverse susceptibilities decrease below the transition temperature. The obtained results naturally explain the temperature dependence of the magnetic susceptibility observed in CeT 2 Al 10 (T =Ru,Os,Fe) family.
Magnetism in the dilute Kondo lattice model
Physical Review B, 2004
The one dimensional dilute Kondo lattice model is investigated by means of bosonization for different dilution patterns of the array of impurity spins. The physical picture is very different if a commensurate or incommensurate doping of the impurity spins is considered. For the commensurate case, the obtained phase diagram is verified using a non-Abelian density-matrix renormalization-group algorithm. The paramagnetic phase widens at the expense of the ferromagnetic phase as the f-spins are diluted. For the incommensurate case, antiferromagnetism is found at low doping, which distinguishes the dilute Kondo lattice model from the standard Kondo lattice model.