Nonmagnetic Dilution Research Articles

Evolution from long-range order to Kondo lattice inGd1−xYbxNi2B2C

The evolution from a local moment, magnetically ordered ground state (below 20 K), in ${\mathrm{GdNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ to a Kondo lattice in ${\mathrm{YbNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ compounds $(\ensuremath{\gamma}\ensuremath{\approx}530{\mathrm{m}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{}\mathrm{K}}^{2},{T}_{N}<0.03\mathrm{K})$ was studied on single crystals of the ${\mathrm{Gd}}_{1\ensuremath{-}x}{\mathrm{Yb}}_{x}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ series by thermodynamic and transport measurements with particular attention to the concentration range in which there is the development of a spin-glass state. Results are compared with an example of magnetic to nonmagnetic rare-earth dilution in the ${\mathrm{Gd}}_{1\ensuremath{-}x}{\mathrm{Lu}}_{x}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ series.

Electronic Structures of the Kondo Semiconductor YbB12: Temperature and Non-Magnetic Dilution Effects

We present our optical studies on the Kondo semiconductor YbB 12 , and on the “diluted” compounds Yb 1- x Lu x B 12 (0 ≤ x ≤1). The optical conductivity spectrum σ(ω) of YbB 12 is characterized by the opening of an energ gap of ∼20 meV below 80 K, and a pronounced mid-infrared (IR) peak which is also strongly temperature ( T ) dependent. For Yb 1- x Lu x B 12 with increasing x , the clear gap for x =0 is rapidly filled in from the bottom, and the mid-IR peak shows large red shifts. It is shown that increasing T and increasing x have qualitatively very similar effects on the energy gap and the mid-IR peaks. We discuss the evolutions of Yb 4 f -related electronic states near the Fermi level with T and x , and its relation to the gap evolution.

Quasi-elastic scattering from unconventional antiferromagnetic compounds

Certain apparently simple antiferromagnets show a broad range of fluctuating behaviour at temperatures below the mean field interaction energy, generally due to particular lattice properties such as low dimensionality or geometric frustration. In such systems competition between qualitatively different ground states is common. A ‘spin-liquid’ ground state, characterised in the ideal case by a total absence of elastic response and possibly by a gap for magnetic excitations can occur while, due to various reasons including non-magnetic dilution, a tendency to ordering can be recovered. A common feature originating from the competing ground states of these unconventional spin systems is the appearance of a fluctuation energy scale well below the typical nearest neighbour interactions, even in the absence of an associated development of long-range spatial order. In this paper we outline the qualitative differences of such a magnetic response with respect to the standard paramagnet-critical regime-ordered state sequence. We examine representative examples of these type of studies on some antiferromagnetic chain compounds and frustrated antiferromagnets. In all these cases we demonstrate the importance of energy resolved observation in understanding the ordered, elastic diffuse and quasi-elastic components of the magnetic scattering.

Interplay between non-magnetic dilution and pressure effects in magnetism of UCoAl

Effects of external hydrostatic pressure and Y(Lu) substitutions for U on magnetism in U 1− x Y(Lu) x CoAl compounds were studied. Y and Lu doping of UCoAl leads to a gradual development of ferromagnetism in a limited concentration range. Reentrant metamagnetism of the UcoAl type is observed in the ferromagnetic U 1− x Y(Lu) x CoAl compounds after application of a sufficient external pressure.

Localized canting effect in Zn-substituted Ni ferrites

A model of three sublattices (A, B and B′) to describe the magnetic behavior of mixed Ni–Zn ferrites is presented. It is proposed that only sublattice B′ is affected by canting, due to the substitution of Zn 2+ ions in sublattice A. The cases where: (i) only Fe 3+ ions are found in B′, and (ii) B′ is occupied by Fe 3+ and Ni 2+ ions are considered. The two-sublattice model with canting in sublattice B is presented for comparison with cases (i) and (ii). The canting angle θ L is calculated from energetic considerations, assuming that the J ij ion-to-ion interaction energies are not modified by the substitution of Zn 2+ ions in sublattice A. The number of Bohr magnetons per molecule, n B, and the Curie temperature, T c, are predicted as a function of Zn content, z. The experimental values of n B as well as the results for T c are satisfactorily reproduced by the model described in (i). Results on Zn-substituted Li ferrite are also mentioned. It is found that additional considerations on the interactions are needed for this system, as lithium acts as a non-magnetic dilution in the octahedral sublattice.

Magnetic order and reorientation transitions in the diluted Laves hydride(DyxY1−x)Mn2D4.4

We have studied the influence of the nonmagnetic dilution in the rare-earth sublattice on the interplay between the rare-earth and Mn magnetism in the Laves hydrides $({\mathrm{Dy}}_{x}{\mathrm{Y}}_{1\ensuremath{-}x}){\mathrm{Mn}}_{2}{\mathrm{D}}_{4.5}.$ The N\'eel temperature does not vary significantly with the dilution. Mn sublattice imposes a collinear magnetic order in the Dy sublattice even in the strongly diluted samples $(x=0.05).$ In contrast, the direction of the magnetic moments depends on the Dy concentration. In the concentration range $0.1<x<0.8$ we observe a reorientation transition at some intermediate temperature below the N\'eel temperature. From the magnetic phase diagram we conclude that both rare-earth and Mn anisotropies should be taken into account to explain the magnetic properties of the binary hydrides $R{\mathrm{Mn}}_{2}{\mathrm{H}}_{4.5}.$

Mössbauer effect evidence of spin reorientation in (Er1 − xCex)2Fe14B intermetallic compounds

Spin reorientation in (Er1 − xCex)2Fe14B system, originating from competition between the magnetic anisotropies of the erbium and iron sublattices, was observed by the 57Fe Mössbauer spectroscopy below room temperature. The spin transition temperature is lowered by non-magnetic dilution within the rare earth crystal sublattice, caused by substitution of cerium for erbium. There is evidence that the process proceeds not at a discrete temperature but in a wide temperature range. The discrete values of the 57Fe hyperfine interaction parameters, derived from Mössbauer absorption spectra, are consistent with localized interactions of iron atoms with their nearest neighbours. It was found that substitution of cerium for erbium slightly reduces hyperfine magnetic fields at iron sites and it only has a minute influence on the values of the isomer shifts and quadrupole interactions.

Diluted quasi-one-dimensional classical antiferromagnets.

We consider the effect of the exchange disordering, mainly the nonmagnetic dilution, on the low-temperature properties of the quasi-one-dimensional classical antiferromagnets. Dynamic susceptibility expansion in defect concentration shows that even a low level of doping substantially changes the spin-wave stiffness and the transverse susceptibility. We investigate the nonperturbative concentration dependencies of the spin-wave velocities and susceptibility arising when the impurity concentration exceeds the small characteristic value ${\mathit{x}}_{0}$= \ensuremath{\surd}${\mathit{J}}_{\mathrm{\ensuremath{\perp}}}$/${\mathit{J}}_{\mathrm{\ensuremath{\parallel}}}$ . A general result, pertinent to the true three-dimensional antiferromagnets as well, concerns the excitation spectrum of the disordered nonfrustrated antiferromagnets with nonfluctuating anisotropy. In this case the hydrodynamical description of long-wave excitations breaks down, and the spin waves with energies near the anisotropy gap are overdamped.

Magnetic properties of (Cr1-xTix)5S6 and (Cr1-xVx)5S6

Abstract Nonmagnetic dilution effects of Ti and V atoms for Cr in CrS 1.18 are investigated by means of magnetic measurements. Magnetic phase diagrams and molar Curie constants C mole are determined. A considerable difference in x -dependences of C mole for both systems is briefly discussed in view of localization-delocalization concept of 3d electrons.