Itinerant-electron Antiferromagnet Research Articles

Phenomenological model of longitudinal spin fluctuations in itinerant antiferromagnets

We present the phenomenological analysis of the spectrum of longitudinal spin fluctuations in isotropic itinerant electron antiferromagnets with account of spin anharmonicity giving rise to coupling of transverse and longitudinal normal modes. The spectrum consists of a quasielastic part forming a central peak or a dip, depending on temperature and the Landau relaxation rate. Effects of spin fluctuation coupling also give rise to an inelastic part of the spectrum which has a form of resonances or antiresonances near the magnon frequencies related to non-propagating longitudinal excitations.

Quantum Phase Transition in the Itinerant Antiferromagnet(V0.9Ti0.1)2O3

Quantum-critical behavior of the itinerant electron antiferromagnet (V0.9Ti0.1)2O3 has been studied by single-crystal neutron scattering. By directly observing antiferromagnetic spin fluctuations in the paramagnetic phase, we have shown that the characteristic energy depends on temperature as c1 +c2T3/2, where c1 and c2 are constants. This T3/2 dependence demonstrates that the present strongly correlated d-electron antiferromagnet clearly shows the criticality of the spin-density-wave quantum phase transition in three space dimensions.

Thermal expansion of itinerant nearly and weakly antiferromagnetic materials

Magnetic thermal expansions of itinerant electron antiferromagnets are discussed along the Grüneisen's approach to the thermal expansions due to lattice vibrations. We show that the thermal expansion consists of two terms, ω 0 ( T ) , that corresponds to the Moriya–Usami's result, and a new term ω t ( T ) derived for ferromagnets recently. Comparison of these terms shows that the second term becomes dominant at low temperatures around the magnetic instability point, leading to the T 2 -linear behavior there for nearly antiferromagnetic compounds.

Uranium Nitride — A Spin Polarized Weak Itinerant Electron Antiferromagnet with Strongly Correlated Electrons

AbstractFor Abstract see ChemInform Abstract in Full Text.

Uranium nitride—a spin polarized weak itinerant electron antiferromagnet with strongly correlated electrons

A brief survey of anomalous properties of uranium nitride—a collinear metallic antiferromagnet with NaCl-structure is presented and argued that it must be regarded as a weak antiferromagnet with polarized itinerant electrons. It is shown that this new weak itinerant antiferromagnet appears to be a very simple magnetic system, well understood within the Fermi liquid picture of spin polarized 5 f-electrons, and may be used as a model to study basic problems of strongly correlated systems.

μSR and neutron scattering studies of spin dynamics

Aspects of the complementary roles of muon and neutron beam techniques in the investigation of magnetic systems are presented and discussed, particularly in the context of studies of spin fluctuations and spin glass-like behaviour in itinerant electron antiferromagnets (e.g. YMn 2, β-MnAl) and ferromagnets (e.g. Ni 3Al).

Antiferromagnetism and low-temperature specific heatof β-Mn1−xIrxalloys

The site preference of Ir, the temperature dependence of magnetic susceptibility and thelow-temperature specific heat of β-Mn1−xIrxalloys have been investigated. In Mn1−xIrx alloys, theβ-phase existsbelow x = 0.102.From x-ray diffraction patterns, almost all Ir atoms aresubstituted at site 1 in the β-Mnlattice. The electronic specific heat coefficient γ is proportional to the Néeltemperature TN inthe form TN3/4in regions of low-Ir concentration. With increasingx, however, the gradualdecrease in γ leads toa relative increase in γfrom the straight line. Therefore, it is concluded that the magneticstate of the β-Mn1−xIrxalloys varies from a weak itinerant-electron antiferromagnet to an intermediateantiferromagnet with increasing Ir concentration. The point to observe is that the γ versusTN3/4plots give a universal line for all the β-Mnalloy systems over the entire concentration range.

Magnetic and charge structures in itinerant-electron magnets: Coexistence of multiple spin-density and charge-density waves

A theory of Kondo lattices is applied to studying possible magnetic and charge structures of itinerant-electron antiferromagnets. Even helical spin structures can be stabilized when the nesting of the Fermi surface is not sharp and the superexchange interaction, which arises from the virtual exchange of pair excitations across the Mott-Hubbard gap, is mainly responsible for magnetic instability. Sinusoidal spin structures or spin density waves (SDW) are only stabilized when the nesting of the Fermi surface is sharp enough and a novel exchange interaction arising from that of pair excitations of quasi-particles is mainly responsible for magnetic instability. In particular, multiple SDW are stabilized when their incommensurate ordering wave-numbers $\pm{\bf Q}$ are multiple; magnetizations of different $\pm{\bf Q}$ components are orthogonal to each other in double and triple SDW when magnetic anisotropy is weak enough. Unless $\pm 2{\bf Q}$ are commensurate, charge density waves (CDW) with $\pm 2{\bf Q}$ coexist with SDW with $\pm{\bf Q}$. Because the quenching of magnetic moments by the Kondo effect depends on local numbers of electrons, the phase of CDW or electron densities is such that magnetic moments are large where the quenching is weak. It is proposed that the so called stipe order in cuprate-oxide high-temperature superconductors must be the coexisting state of double incommensurate SDW and CDW.

Development of itinerant-electron antiferromagnetism in the approach to metal–insulator transition in metallic NiS 2− xSe x as studied by [formula omitted] NMR

From the T-dependences of the Knight shift and 1/ T 1 T of 77 Se NMR, the approach to the metal–insulator transition from the metallic side in NiS 2− x Se x has been clarified to be characterized by the development of antiferromagnetic spin fluctuation.

Electronic transition inLa1−xSrxTiO3

The transition with increasing x in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{TiO}}_{3}$ from an antiferromagnetic, p-type polaronic conductor to an n-type metal with an enhanced Pauli paramagnetism was investigated by monitoring changes in structure, magnetic properties, and, under different hydrostatic pressures, the resistance and thermoelectric power of ceramic samples. We conclude that ${\mathrm{LaTiO}}_{3}$ is an itinerant-electron antiferromagnet and the transition is first order with a phase separation associated with cooperative oxygen-atom displacements that segregate strongly correlated states from Fermi-liquid states. The N\'eel temperature ${T}_{N}\ensuremath{\approx}145\mathrm{K}$ decreases precipitously to 100 K at the phase limit $x=0.045\ifmmode\pm\else\textpm\fi{}0.005;$ the two-phase domain extends over the compositions $0.045l~xl~0.08.$

Electron Transport Properties of La1-xSrxTiO3 Under Hydrostatic Pressure

ABSTRACTThe temperature dependence of the resistance and thermoelectric power under hydrostatic pressure between 10 and 300 K are reported for two compositions, x = 0.044 and x = 0.05, of the narrowband system La1-xSrxTiO3. The application of hydrostatic pressure at room temperature induces a transition from a positive p-type to a negative n-type thermoelectric power for x = 0.044. This behavior is interpreted within a model of itinerant-electron antiferromagnetism in LaTiO3.

Invar-like behaviours in an itinerant-electron antiferromagnet

By making use of the Landau - Ginzburg energy expansion up to the sixth power of the sublattice magnetization density, the spontaneous volume magnetostriction and the dependence on pressure of the Néel temperature in an itinerant-electron antiferromagnet are discussed. The antiferromagnetic moment is found to show first-order and second-order transitions at - according to the values of the Landau coefficients. It is shown that the difference between the spontaneous volume magnetostrictions at T = 0 and is large and the P-dependence of becomes anomalously large when a certain condition is satisfied by the Landau coefficients.

An ultrasonic study of the Néel transition in dilute Cr-Al alloy single crystals

Measurements are reported of the temperature variation of the sound velocity and ultrasonic attenuation coefficient of Cr-Al alloy single crystals containing 1.2, 1.9, and 2.6 at % Al. The results close to the Néel temperature are not satisfied by existing theories for the critical behavior of itinerant electron antiferromagnets.

MAGNETIC BEHAVIOUR OF A Cr+1.6 at.% Si SINGLE CRYSTAL

Measurements of thermal expansion and velocity of sound around the Néel temperature (TN) of a Cr+1.6 at.% Si single crystal are presented. A weak continuous transition superimposed on a sharp first-order discontinuity was observed in the thermal expansion near TN. The continuous component is accurately described by a critical exponent power law. The sound velocity diverges sharply near TN in contrast with theoretical predictions for Cr-like itinerant electron antiferromagnets.

Spin-wave spectrum of a two-dimensional itinerant-electron antiferromagnet based on a CuO2 layer: Approximate mapping onto an effective Heisenberg model.

We calculate the spin-wave spectrum of a ${\mathrm{CuO}}_{2}$ antiferromagnetic layer with one hole per Cu site, as described by a three-band Hubbard model with a local repulsion U at Cu sites, a hopping integral t between Cu and O sites, and a charge-transfer energy \ensuremath{\Delta} between Cu and O sites, by locating the poles of the transverse spin correlation function at given momentum and frequency within the random-phase approximation. We find that the calculated spin-wave spectrum can be fitted rather accurately over the whole Brillouin zone by the corresponding spectrum of a localized spin-1/2 Heisenberg model with a suitably chosen effective exchange coupling ${\mathit{J}}_{\mathit{e}\mathit{f}\mathit{f}}$, the relative error \ensuremath{\Delta}${\mathit{J}}_{\mathit{e}\mathit{f}\mathit{f}}$/${\mathit{J}}_{\mathit{e}\mathit{f}\mathit{f}}$ introduced by the fitting being smaller than 15% when \ensuremath{\Delta}/t+2U/t\ensuremath{\ge}5. With the values for U, t, and \ensuremath{\Delta} appropriate to ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$, we find ${\mathit{J}}_{\mathit{e}\mathit{f}\mathit{f}}$\ensuremath{\simeq}0.12 eV and \ensuremath{\Delta}${\mathit{J}}_{\mathit{e}\mathit{f}\mathit{f}}$/${\mathit{J}}_{\mathit{e}\mathit{f}\mathit{f}}$\ensuremath{\simeq}4.5%, in good agreement with the estimated experimental values. Our results suggest that some caution is in order when embracing a localized-spin model to describe the magnetic properties of the parent compounds of oxide superconductors.

Magnetic excitations in the triangular antiferromagnet Mn 3Sn

The intermetallic compound Mn 3Sn has a triangular spin configuration below the Néel point at 420 K. Below 230 K, this triangular spin arrangement remains within each hexagonal layer, but the spins rotate about the c axis with a period of about 10 c 0. We have studied the magnetic excitations of this itinerant electron antiferromagnet along high-symmetry directions at temperatures above and below the helical phase transition T h. At 295 K, the spin-wave dispersion is approximately linear in q along {100} and quadratic in q along the {1, 0, ζ} and {1, 1, ζ} directions. The spin-wave energies at 295 K can be described by (ℏω) 2=Δ 2+A 2q 2 and ℏω=Δ+Bq 2 where the anisotropy gap Δ=4.3 meV, A≅100 meV Å for <100}, A≅135 meVÅfor {110}, and B=130meVÅ 2 for {1, 0, ζ} and {1, 1, ζ} Below T h, the zone center shifts to the satellite positions of the helical structure, and the dispersion along {1, 0, ζ} becomes linear in q withℏω≅95 q [meV].

Mössbauer spectroscopy at high pressure on magnetic neptunium compounds

Abstract The Mossbauer transition in127Np was used to study the volume dependence of magnetic parameters like the hyperfine field B and the ordering temperature Tc or TN in intermetallic compounds of Np. Typical examples are NpOs2, NpAl2, NpCo2Si2, NpAs and NpSn3-. The spectrometer employed a clamp device with a high pressure cell based on opposite boron-carbide anvils and allowed measurements up to 100 kbar at temperatures between 300 K and 2 K. The data were mainly used to gain information on the degree of delocalization of 5f-electrons, that is, whether the compound resembles in its magnetic properties more a typical rare earth (4f) or a 3d transition material. Most of the high pressure results can basically be understood in terms of accepted models of 5f-electron structure. A most surprising behavior, however, was seen for NpSn3-. Although this compound is considered on account of its bulk magnetic properties a prototype itinerant electron antiferromagnet, the pressure dependencies of Bhf and TNreveal...

The influence of the spin-glass state on the itinerant-electron antiferromagnetic state

The dependence of the critical temperature on the concentration for an itinerant-electron antiferromagnet containing frozen magnetic impurities in the spin-glass state has been calculated. We showed that important deviations from the Abrikosov-Gor'kov theory appear due to the averaging procedure. The theoretical results can be applied to explain the decreasing of the Néel temperature in the Cr alloys with the rare earth metals.

Quantitative Aspects of the Theory of Weak Itinerant Antiferromagnetism

The self-consistent renormalization (SCR) theory of spin fluctuations in itinerant electron antiferromagnets is formulated in a rotationally invariant way with four independent parameters associated with the band structure and the exchange enhancement factor. Various physical quantities are expressed in terms of these parameters and possible quantitative comparisons with experiment are discussed. Numerical calculations for some typical examples are performed for the temperature dependences of the staggered magnetic susceptibility above T N and the staggered magnetization below T N .

Itinerant antiferromagnetism of the Ti-Si solid solutions

Magnetic susceptibility measurements of Ti-Si solid solutions are reported. Silicon by alloying acts on the Néel temperature of pure titanium. The Néel temperature decreases monotonously with increasing silicon concentration. The experimental and theoretical magnetic phase diagrams are in good agreement. This means that the antiferromagnetism of the Ti-Si solid solutions can be interpreted in terms of itinerant electron antiferromagnetism of the SDS type magnetic structure.