Effective Bohr Magneton Number Research Articles

Spin wave dispersion and energy bands in fcc metals

The spin wave dispersion along the principal axis directions from the center to the surface of the Brillouin zone is studied numerically for the fee metals, the study being based on the 3d energy bands of nickel as calculated by Hanus. The dispersion dependence on the splitting between the up- and down-spin bands and on the magnitude of the interatomic exchange is given. Fourier analysis of the dispersion curves indicates that an effective exchange interaction is long range. It is also found that for sufficiently large interatomic exchange, the spin wave spectrum intersects the continuum of single particle excitations and that the single particle excitations will be thermally excited at temperatures well below the Curie point. Using experimental spin wave mass values for the nickel-copper alloys, the results of this dispersion calculation indicate that the splitting between the up- and down-spin bands decreases more rapidly with increasing copper than does the effective number of Bohr magnetons per atom. This implies that the effective band splitting interaction is alloy dependent.

Structural and magnetic properties of Mg_{0.8-x}M_{0.2}Ni_xFe_2O_4 (M = Zn, Mn) ferrite powders

Structural and magnetic properties of Mg_{0.8-x}M_{0.2}Ni_xFe_2O_4 (M = Zn, Mn; x = 0, 0.2, 0.4, 0.6, 0.8) ferrite powders, prepared by solid state reaction method, were studied. The variations of lattice parameter, X-ray density, crystallite size, saturation magnetization, effective number of Bohr magneton, and coercivity with Ni content were investigated. The role of grain size was found to be crucial in the behavior of coercivity.

Dynamical Coherent-Potential Approximation and Tight-Binding Linear Muffintin Orbital Approach to Correlated Electron System

Dynamical coherent-potential approximation (CPA) to correlated electrons has been extended to a system with realistic Hamiltonian which consists of the first-principles tight-binding linear muffintin orbital (LMTO) bands and intraatomic Coulomb interactions. Thermodynamic potential and self-consistent equations for Green function are obtained on the basis of the functional integral method and the harmonic approximation which neglects the mode–mode couplings between the dynamical potentials with different frequency. Numerical calculations have been performed for Fe and Ni within the second-order dynamical corrections to the static approximation. The band narrowing of the quasiparticle states and the 6 eV satellite are obtained for Ni at finite temperatures. The theory leads to the Curie–Weiss law for both Fe and Ni. Calculated effective Bohr magneton numbers are 3.0 µ B for Fe and 1.2 µ B for Ni, explaining the experimental data. But calculated Curie temperatures are 2020 K for Fe and 1260 K for Ni, being ...

Electrical conductivity and magnetic properties of La1 − x Ca x Mn1 − y Fe y O3 ceramic samples (x = 0.67, y = 0, 0.05)

The temperature dependences of the magnetic susceptibility χ(T) and the electrical resistivity ρ(T) of ceramic samples of La1 − xCaxMnO3 with x = 0.67 (LCMO) and La1 − xCaxMn1 − yFeyO3 with x = 0.67 and y = 0.05 (LCMFO) are investigated in magnetic fields B = 50–105 G and the temperature range T = 4.2–400 K. Both samples undergo a transition from the paramagnetic state to a state with charge (orbital) ordering (CO) at temperatures TCO ≈ 272 K for LCMO and TCO ≈ 222 K for LCMFO. The behavior of the paramagnetic phase in the temperature range 320–400 K for LCMO and 260–400 K for LCMFO is described by the Curie-Weiss law with effective Bohr magneton numbers peff = 4.83 μB (LCMO) and 4.77 μB (LCMFO), respectively. The disagreement between the observed positive Weiss temperatures (θ ≈ 175 K (LCMO) and θ ≈ 134 K (LCMFO)) and negative Weiss temperatures required for the antiferromagnetic ground state can be explained by the phase separation and transition to the charge-ordered state. The magnetic irreversibility for T < TCO is accounted for by the existence of a mixture of the ferromagnetic and antiferromagnetic phases, as well as the cluster glass phase. At low temperatures, doping with iron enhances the frustration of the system, which manifests itself in a more regular behavior of the decay rate of the remanent magnetization with time. The temperature dependence of the electrical resistivity in the range of the charge-ordered phase conforms to the variable-range hopping model. The behavior of the electrical resistivity is governed by the complex structure of the density of localized states near the Fermi level, which includes a soft Coulomb gap Δ = 0.464 eV for LCMO and 0.446 eV for LCMFO. It is established that the ratio between the localization radii of charge carriers a for LCMFO and aund for LCMO is a/aund = 0.88.

Magnetic susceptibility of several germanium garnets

The general chemical formula for a garnet oxide is represented as {C} 3[A] 2(D) 3O 12, where the three cation sites are C-, A-, and D-sites. These cation sites are surrounded by oxygen ions O 2− at dodecahedron, octahedron and tetrahedron, respectively. Several germanium garnets of {Ho 2Mg}[Mg] 2(Ge) 3O 12, {Tm 2Mg}[Mg] 2(Ge) 3O 12, {Ca} 3[Ho] 2(Ge) 3O 12, {Ca} 3[Tm] 2(Ge) 3O 12, {Sr} 3[Ho] 2(Ge) 3O 12, and {Sr} 3[Tm] 2(Ge) 3O 12 are synthesized. Magnetic susceptibilities of these garnets obey well the Curie–Weiss law. Paramagnetism with negative intercept of the 1/ χ versus T curve is observed. The results indicate that all the Ho and Tm ions possess tri-valence states as Ho 3+ and Tm 3+ ions with the effective number of Bohr magnetons p eff=11/Ho 3+-ion and p eff=7.6/Tm 3+-ion approximately, regardless of the consequences of the site preference problem.

Origin of Weak Ferromagnetism in YbxFe4Sb12, Relationship between Weak Ferromagnetism and Filling Ratio x

The magnetization and specific heat of single-crystalline samples of filled-skutterudite compounds Yb x Fe 4 Sb 12 were measured. Six single crystals with the filling ratio of Yb, x , from 0.875 to 0.910 were prepared. The weak ferromagnetism of Yb x Fe 4 Sb 12 appearing at low temperatures was found to strongly correlate with x ; with increasing x from 0.875 to 0.910, the transition temperature, T C , decreases from 17 to 5 K and the weak-ferromagnetic moment, m 0 , decreases from 0.066 to 0.005 µ B /Fe. From these trends, both T C and m 0 were expected to reach zero at the critical concentration, x c =0.93. In the temperature dependence of the specific heat, no anomaly at T C was observed, reflecting that m 0 is extremely small compared with the effective Bohr magneton number. With the application of pressure, the T C of the sample with x =0.882 increases rapidly, with the ratio of d T C /d P =+5.27 K/GPa. This weak ferromagnetism of Yb x Fe 4 Sb 12 originates from the itinerant 3d electrons of Fe in anions [Fe 4 Sb 12 ].

Spin-liquid behavior in the spinel-type Cu(Cr 1−xZr x) 2S 4

A spinel mixed crystal CuCrZrS 4 has an asymptotic Curie temperature θ≈62 K with an effective number of Bohr magnetons p eff=3.70/Cr-atom. The most striking feature is the absence of peak or step in the heat capacity at temperatures close to 62 K. The geometrical spin frustration is introduced through antiferromagnetic interaction due to the substitution of nonmagnetic Zr for Cr atom, on the B sites forming a network of linked tetrahedra. The magnetizations in field-cooled (FC) and zero-field-cooled (ZFC) are observed with irreversibility in T ⩽ T g (≈10 K). This paper will present the magnetic properties of mixed crystals Cu(Cr 1− x Zr x ) 2S 4 focused on the specimen for x=0.45 which has θ=164 K and p eff=2.37/Cr-atom. Experimental results lead to a physical picture for Cu(Cr 1− x Zr x ) 2S 4 that a spin-glass state for T⩽ T g, a spin-liquid state which remains unordered in a cooperative paramagnetic state termed a spin-liquid state for T g⩽ T⩽ θ, and a spin-gas state for θ⩽ T with a Curie–Weiss law. The spins for T g⩽ T⩽ θ will exhibit subtle correlations in the absence of long-range order and may form into clusters of frustrated system. In comparison with a typical ferromagnet for T⩽ θ, the fairly slender magnetization as a function of temperature is observed in a constant field. The difference of hysteresis curves between the spin-glass state for T⩽ T g and the spin-liquid state for T g⩽ T⩽ θ is clearly detected in low magnetic field.

Influence of the phase separation effect on low-field magnetic properties of La 1−xBa xMnO 3

Magnetic susceptibility, χ ( T ) , is investigated in ceramic La 1− x Ba x MnO 3 (LBMO) with x = 0.02 – 0.25 in the range of fields B = 10 – 80 G and temperatures T = 5 – 310 K . All samples exhibit a paramagnetic (PM) to ferromagnetic (FM) transition with T C increasing with x from 177 K ( x = 0.02 ) to 295 K ( x = 0.25 ) and magnetic irreversibility decreasing below T C with increasing x . In the PM phase an interval of the Curie–Weiss behavior of χ ( T ) with an effective Bohr magneton number, p eff ∼ 30 – 40 , is observed above T 1 ∼ 260 – 290 K . Below T 1 and down to T cr ∼ 190 – 220 K the susceptibility follows the scaling law χ - 1 ( T ) - χ - 1 ( T C ) ∼ ( T / T C - 1 ) γ with γ = γ 1 ≈ 1.4 corresponding to a three-dimensional (3D) Heisenberg spin system. Below T cr, χ ( T ) obeys the same scaling law as for T > T cr , but with another value of γ = γ 2 ≈ 1.7 – 1.8 , characteristic of a 3D percolation system. The temperature dependence of the susceptibility observed in the PM phase is explained by small FM particles embedded in the host LBMO matrix above T 1. The size of these particles increases between T 1 and T cr up to nanometer scale, forming critical percolation clusters below T cr. The magnetic irreversibility is connected to a mixed, FM and cluster-glass, phase.

Magnetic-field-drivenx≈1/8anomaly of superconductivity inLa2−x−ySrxMnyCuO4

Dependence of superconducting transition temperature ${T}_{c}(\mathrm{y})$ on an applied magnetic field B is investigated in ${\mathrm{La}}_{2\ensuremath{-}x\ensuremath{-}y}{\mathrm{Sr}}_{x}{\mathrm{Mn}}_{y}{\mathrm{CuO}}_{4}$ with $0&lt;~y&lt;~0.05$ and $x+y=0.15.$ A strong linear decrease of ${T}_{c}$ with increasing B is observed around the manganese concentration $y=0.025,$ which correlates with the $x\ensuremath{\approx}1/8$ anomaly in ${\mathrm{La}}_{1.875}{\mathrm{Sr}}_{0.125}{\mathrm{CuO}}_{4}.$ At this value of y the number of ${\mathrm{Mn}}^{3+}$ pairs, the effective Bohr magneton number ${p}_{\mathrm{eff}},$ and the antiferromagnetic Curie temperature $\ensuremath{\Theta}$ attain their maxima, suggesting that local magnetic order of the Mn system is responsible for the observed effect.

Effective spin quantum numbers in iron, cobalt and nickel

The known macroscopic data for the temperature dependence of the normalized spontaneous magnetization, m s( T), of iron, cobalt and nickel are reconsidered and compared with our normalized zero-field hyperfine field data, h hf( T), obtained by Mössbauer spectroscopy or nuclear magnetic resonance. It is observed that for all three metals h hf( T) is not proportional to m s( T) and systematically smaller than m s( T). This is attributed to smaller magnetic interactions in the domain walls compared to the volume of the domains. The temperature dependence of m s( T) and h hf( T) can be described in the whole range 0< T< T C by a few temperature power functions with analytical changes (crossovers) at the intersections of these functions. Below the critical power law, m s∼( T C− T) β , further power functions of the absolute temperature according to m s( T)= A− cT ε , follow. From the observed rational exponents ε it can be concluded whether the effective spin is integer or half-integer. Using additionally the known data for the saturation magnetic moments and the effective paramagnetic Bohr magneton numbers it is suggested that for nickel the effective spin is S=1/2 for T→0 but S=1 for higher temperatures including the paramagnetic phase. For iron and cobalt the corresponding values are S=3/2 and 2 .

Magnetic properties of Y-substituted Y xGd 1− xBa 2Cu 3O 7− δ

Measurements on magnetic properties of Y-substituted Y x Gd 1− x Ba 2Cu 3O 7− δ ceramics are performed and effects of Y substitution on the normal and superconducting properties are investigated. The temperature dependence of the normal susceptibility obeys the Curie–Weiss law with antiferromagnetic Weiss temperature, becoming larger with oxygen deficiency as well as Y substitution. The effective Bohr magneton number p e for Gd spins estimated from the temperature-coefficient is fairly close to or slightly larger than the theoretical value of the 8S 7/2 ground state. Substitution of Y atoms to Gd sites seems to basically result in simple dilution of Gd spins, the number p e being not much dependent on the Y substitution. Possible role of diluting magnetism on the T c-improvement in oxygen deficient, Y-substituted Y x Gd 1− x Ba 2Cu 3O 7− δ is discussed. Enhancement of the superconducting magnetization hysteresis and the critical current density with Y substitution is also observed and examined.

On magnetic properties of DyNi5−xAlx (x=0, 1, 1.5, 2, 2.5, 3) intermetallics

The bulk magnetic properties of the DyNi5-xAlx (x=0, 1, 1.5, 2, 2.5 and 3) intermetallic compounds, have been investigated up to 25 K. It has been found that substitution of Ni by Al decreases the Curie temperature for those compounds with the CaCu5 type of crystal structure (x >2) but when the YCo3Ga2 structure type is adopted (x>2), the Curie temperature increases once more at x=2.5. For all alloys, the paramagnetic effective Bohr magneton numbers, peff were found to be close to the free ion value of Dy3+. A complex low temperature magnetic behaviour with a possibility of up to three ordered magnetic states was observed for the alloys with x>2.

Magnetic and transport properties of III–V diluted magnetic semiconductor Ga1−xCrxAs

Magnetic and transport properties of Cr-based III–V diluted magnetic semiconductor Ga1−xCrxAs Cr concentrations up to x=0.10 have been investigated. For all the films, no long-range magnetic order was observed down to 2 K. A sign of paramagnetic Curie temperature is positive, indicating that the dominant magnetic interaction between Cr atoms is ferromagnetic. The effective number of Bohr magneton is estimated to be 5.1±0.4, which is close to that of Cr2+ ion. The magnetization curve shows superparamagnetic behavior at low temperatures. The radius of the local spin order in x=0.034 is estimated to be 1.5–2.0 nm at T=5 K and it decreases with increasing temperature. From Hall effect measurements at room temperature, the magnitude of mobility is estimated to be less than 0.5 cm2/V s. This low mobility strongly suggests that the hopping conductivity is dominant in Ga1−xCrxAs films.

Rietveld refinement and solid state NMR study of Nd-, Sm-, Gd-, and Dy-containing Y zeolites

Na-Y zeolites ion exchanged with rare earth cations (Nd 3+, Sm 3+, Gd 3+, Dy 3+) were studied by X-ray diffraction in order to locate the rare earth cations in the zeolite framework and the resulting changes in its structural properties. The results indicate that the rare earth cations dealuminate the framework differently. This is observed as a decrease in the values of the unit cell parameters, a 0. This systematic decrease in a 0 is related to the rare earth ionic radius and its coordination to the oxygen framework. The correlation between the Si/Al ratio obtained from the Fichtner-Schmittler equation and the ionic radius of the rare earth cations reveals that smaller ionic radii gives higher dealumination and smaller a 0. This is related to hydrolysis constant cation. Samples treated with Dy 3+ cations show a higher level of dealumination than those treated with the other cations (Sm 3+, Gd 3+, Nd 3+). In order to characterize the dealumination process 29 Si and 27 Al magic angle spinning NMR measurements were attempted. Except for the Sm 3+ treated sample, the Nd 3+, Gd 3+, Dy 3+ samples could not have their tetrahedral and octahedral aluminum signal detected due to the high concentration of the paramagnetic ions with large effective number of Bohr magnetons.

Magnetic properties of single crystal CePtGa

Magnetic and transport properties are reported for the first time on single crystal of CePtGa which is isostructural with the Kondo semiconductor CeNiSn. Magnetic susceptibility shows the Curie–Weiss behavior at high temperatures and an effective number of Bohr magneton for trivalent Ce ion and antiferromagnetic order was found below 3.5 K. These behaviors were analyzed in terms of crystalline field. Electrical resistivity shows metallic behavior for all three axes.

Disappearance of magnetic moments in CePd 1− xNi xAl

We present the chemical pressure effect on the specific heat and magnetic susceptibility in the substituted system CePd 1− x Ni x Al. By substitution of 10% of Ni, T N has almost disappeared. Further substitution of Ni drastically diminishes the magnetic moment and the effective number of Bohr magnetons. The entropy integrated up to 10 K is 66% for CePdAl, and it decreases to 3% of R ln 2 with increasing x. The electronic specific-heat coefficient C/ T approaches 1.1 J/mol K 2 for CePd 0.9Ni 0.1Al at low temperatures. Single crystals for x=0.0 and 0.1 have been grown to investigate the magnetic anisotropy.

Magnetic susceptibility of La xCe 1− xF 3 single crystals

The magnetic susceptibility of La x Ce 1− x F 3 single crystals, for 0< x⩽0.5, has been measured from 4 up to 300 K in a magnetic field B≈0.2 T applied parallel to the crystallographic a-axis (perpendicular to the c-axis). The effective Bohr magneton number p eff and paramagnetic Curie temperature θ p have been obtained, using the Curie–Weiss law in the temperature range 100–300 K. The interconfiguration excited energy E ex, the spin-fluctuation temperature T sf, and the g-values, corresponding to three Kramers doublets in the 2 F 5/2 ground multiplet of Ce 3+ ion in La x Ce 1− x F 3 have been determined, using quantum theory of paramagnetic susceptibility. The mixed-valent and crystal field effects influence significantly the g-values. The effect of the dilution of the paramagnetic Ce 3+ ions with diamagnetic La 3+ ions is also discussed.

An Electron and X-Ray Powder Diffraction Study of the Defect Fluorite Structure of Mn0.6Ta0.4O1.65

The oxide Mn0.6Ta0.4O1.65 has been synthesized in air by rapidly cooling a melt from 1400°C, and it has been studied by X-ray powder diffraction (XRPD), selected-area electron diffraction (SAED), high-resolution electron microscopy (HREM), thermal analysis, and measurements of magnetic susceptibility and electrical conductivity. The average structure is that of a cubic fluorite with a=4.9826(3) Å and 18% vacancies on the O atom sites. Prominent diffuse scattering is present in its electron diffraction patterns (EDP's) and a structural model for this scattering is proposed. It is based on ca. 10 Å large microdomains with a pyrochlore type structure which are separated by antiphase boundaries. The magnetic susceptibility shows an antiferromagnetic interaction between the Mn2+ ions and an effective number of Bohr magnetons that increases with temperature. When heated in air at 500°C, the compound is oxidized to the composition Mn0.6Ta0.4O1.75, while retaining a cubic fluorite structure with a=4.8380(4) Å. This latter phase is a semiconductor with an activation energy of 0.64 eV.

Magnetic and electrical properties of a stable Zn-Mg-Ho icosahedral quasicrystal

We investigated the electrical resistivity and the magnetism of heavy-rare-earth-based Zn 60Mg 30Ho 10 F-type icosahedral quasicrystals in the temperature region between 2 K and room temperature below 80 kOe in magnetic field. The maximum value of the electrical resistivity is 159 μΩ cm which is comparatively lower than other quasicrystal systems. Below 15 K, the magnetic-field dependence exhibits a magnetoresistance maximum which has not been observed in quasicrystals studied to date, and the temperature dependence shows a resistance minimum. The temperature dependence of the magnetic susceptibility follows, a Curie–Weiss law between 10 K and room temperature corresponding to the effective number of Bohr magneton 10.6 for every Ho atom in the sample. The earlier mentioned anomalies are considered to be related to the dense and large magnetic moments located at the quasiperiodic lattice.

The Distribution of Cu(II) on Boehmite and Silica Surfaces: Correlating EPR Signal Loss with the Effective Bohr Magneton Number of Sorbed Ions

The effective Bohr magneton number μeffof Cu(II) adsorbed at the boehmite/water interface is 14% to 21% less than anticipated for a uniform dispersal of Cu(II) ions throughout the interface. Insufficient evidence for exchange coupling indicates the lost electron paramagnetic resonance signal intensity must largely result from spin–spin relaxation. Polynuclear Cu(II) clusters at the silica/water interface are superparamagnetic with a blocking temperature between 5 K and 7 K. Superparamagnetic Cu(II) clusters at the silica/water interface do not saturate at magnetic fields as high as 10,000 G.