Magnetic properties of Europium-graphite intercalation compound C6Eu

An ordered state with a complex magnetic structure has been observed below 4CK. The magnetization for H ⊥ c (c; the c-axis) shows a field-induced phase transition from a small magnetic moment state ( ～ 0.6μ_B) at lower fields to a larger moment one ( 2.2 - 2.5μ_B) above 25kG. The transition field depends on temperature and is found to be 5 - 2kG. The magnetization for H//c has only a sublinear field dependence. Above 40K the magnetic susceptibility obeys the Curie-Weiss law with θ = +1.3K and the molar Curie constant C_m = 6.78, which suggests that Eu ion is divalent in C₆Eu.     

Magnetic ordering in uranium monophosphide

The magnetic ordering in uranium monophosphide (UP) has been studied by neutron diffraction from a single crystal in a magnetic field. UP orders at T_N ? 122 ± 0.1 K with the type-I antiferromagnetic structure (+-+-), the ordering taking place in a first-order transition. At T₀ = 22.5 K the ordered magnetic moment jumps from 1.7 μ_B to 1.9 μ_B. With a magnetic field H = 25 kOe applied along the [11&#x0304;10] direction, it is found that UP has the collinear single-$\text{K}$ type-I structure above T₀ and undergoes a first-order transition to the planar double-$\text{K}$ type-I structure, accompanied by a “moment jump” due to the change in the moment direction from <001> to <110>.     

Magnetic properties and 57Fe Mössbauer effect in Lu6Fe23 and Lu6Fe23H8

Hydrogen absorption in the cubic compound Lu₆Fe₂₃ ($\text{a}\text{= 11.936}\text{A}\text{?}$) leads to a ternary hydride of the composition Lu₆Fe₂₃H₈ ($\text{a}\text{= 12.072}\text{A}\text{?}$). The H₂ take-up causes a slight increase in the saturation magnetization corresponding to an increase in Fe moment from 1.54 /u_B to 1.64/u_B per atom. The hydrogen absorption did not lead to a substantial change in the linewidth of the ⁵⁷Fe Mössbauer spectrum. On the basis of the Mössbauer data it was inferred that the H atoms occupy the f-type interstitial holes characterized by a tetrahedron formed of three Lu atoms and one Fe atom. The decrease in hyperfine field upon charging was correlated with an increase in Curie temperature.     

Torque magnetometer measurements of the temperature dependence of induced anisotropy energy and of saturation magnetization in amorphous Fe40Ni40P14B6

Induced anisotropy energy K_u and saturation magnetization M have been measured as a function of temperature T between 77 K and T_c on co$\text{n}$venient specimens of amorphous Fe₄₀Ni₄₀P₁₄B₆ by means of a torque magnetometer. The M vs. T curve is found to follow an anomalously low behaviour with respect to crystalline materials. The exper$\text{i}$mental K_u vs. T curve is well fitted by a M² law, also different from higher power laws typical of crystalline alloys.     

Theory of localized magnetic moments in metals I finite cluster approach

The origin of localized magnetic moments formation in metals is investigated theoretically using a self-consistent local spin density molecular cluster approach. Clusters with up to 55 atoms are employed to describe isolated impurity local moment behavior in the cases of Fe$\text{Ag}$ and Fe$\text{Pd}$. Densities of states and spin magnetic moments were determined and compared with results of spectroscopic (notably photoemission) and magnetization measurements, respectively. In the case of a noble metal host, the spin magnetization density is found to be highly localized around the Fe site; the iron moment is ≈ 3.9μ_B and the polarization of the host Ag atoms is small. In the case of a transition metal host, the iron moment is ≈ 3.2 μ_B but here the strong hybridization of the Fe-3d and Pd-4d states results in a large induced magnetic moment in the host PD metal — in essential agreement with experiment for this giant moment system.     

Anomalous permeability in Polder-Smit region of ferrites

A study of the magneto-microwave Kerr effect on two samples of ferrites lying in the Polder-Smit region gives a negative value of μ', the real part of the transverse diagonal term of permeability tensor. There is a negative peak for μ' at a d.c. magnetization approximately equal to $\text{3}\text{4}$ of the saturation magnetization.     

Polarized neutron study of covalency effects in yttrium iron garnet

Magnetic structure amplitudes of 170 reflections up to sin $\text{θ}\text{λ}\text{= 1.0}\text{A}\text{?}{}^{\mathrm{?1}}$ were measured by polarized neutron diffraction at T = 295K on yttrium iron garnet. The data set was completed by model calculations and the magnetization density was determined. The magnetic moments obtained by integration and refinement are considerably reduced on both iron sites due to charge density transferred from intervening ligand ions. A residual moment of uncancelled spin of (0.032 ±0.004) μ_B is observed on the oxygen ion. Evidence for magnetization density on the oxygen atom and between oxygen and tetrahedral iron was found. A qualitative discussion in terms of a molecular orbital model is given. A further data set collected at 4.2K showed equally a magnetic moment lower than expected for the free ion.     

Magnetic studies in amorphous GdxY1−x alloys

We report here our magnetic study on amorphous Gd_xY_1?x alloys with x = 0.17 and 0.70. The alloy with x = 0.17 is paramagnetic down to 4.2 K. For x = 0.70, magnetization shows a peak in low magnetic fields (H < 0.3 T). Magnetic saturation is difficult to obtain even for fields up to 15 T. An extrapolated value gives a moment of $\text{6.2 μ}{}_{\mathrm{B}}\text{Gd at}$. T_c is about 70 K. This led us to the conclusion that ferromagnetic and antiferromagnetic clusters are present in this alloy. The results are discussed by comparing them with crystalline Gd-Y alloys and amorphous Gd-Al, Gd-Au, etc. The effect of Y seems to be specific.     

Non-linear magnetization dynamics of ferromagnetic insulators at parallel pumping

The non-linear dynamic equation for weakly anisotropic ferromagnetic insulators at parallel pumping in the region of frequencies less than that of the parametric resonance is derived. This equation is used for solving some non-linear problems. The process of the non-linear relaxation of magnetization is considered. The non-linear loss in energy in ferromagnets is studied in the low-frequency region ωτ_∥ ? 1, where τ_∥ is the time relaxation of magnetization connected with the dipole-dipole interaction. In the frequency region ωτ_∥ ? 1 a new type of instability is found. If the amplitude of the variable magnetic field $\text{H(t) =}\text{H}\text{+ h}\text{cos}\text{ωτ}$ satisfies the condition $\text{h}\text{H}\text{? Z}{}_{\mathrm{<mtext>c</mtext>}}\text{≈ 2}$, then the ferromagnet is characterized by the stationary homogeneous value of magnetization. In the amplitude region $\text{h/}\text{H > Z}{}_{\mathrm{<mtext>c</mtext>}}$, this state is unstable and the magnetization starts rotating. At the threshold of instability the magnetic state changes abruptly. The loss in energy in the stability region is found.     

Magnetic field dependence of the nuclear spin—lattice relaxation of 93mMo and 94,95Tc in Fe

The nuclear spin—lattice relaxations of ^93mMo$\text{Fe}$ and ^{94, 95}Tc$\text{Fe}$ at T ? 10 mK have been investigated with frequency- modulation-pulsedNMR on oriented nuclei as a function of an external magnetic field B₀. In the range 0?B₀?6kG the relaxation constant varies by a factor >10 and ?6 for ^93mMo$\text{Fe}$ and ^94,95Tc$\text{Fe}$, respectively. The high-field Korringa constants for ^93mMo, ⁹⁴Tc and ⁹⁵Tc in Fe were determined to be 2.5(4), 1.3(4) and 0.55(10) sK.     

Magnetically induced phase transitions in LaCoO<Subscript>3</Subscript> in fields of up to 500 T

The differential magnetization of LaCoO₃ in magnetic fields of up to 500 T has been measured at a temperature of 4.2 K. The magnetization curve reveals several features which suggest a complex pattern of the transition of LaCoO₃ from the low-spin state to the high-spin state. The magnetic moment starts to grow in fields above 50 T to reach a plateau in the 130–240-T region, after which the magnetic moment continues to rise up to saturation in fields ∼500 T.     

Further neighbour interactions in the quasi b.c.c. Heisenberg ferromagnets M2 Cu X4 · 2H2 O (M = NH4, K,Rb or Cs; X = Cl or Br)

The Curie-Weiss constant θ of the quasi b.c.c., $\text{S =}\text{1}\text{2}$, Heisenberg ferromagnets, (NH₄)₂ Cu Br₄ · 2H₂ O and Rb₂ Cu Br₄ · 2H₂ O, have been derived from measurements of the susceptibility in the paramagnetic region (4.2 < T < 100 K) and of the high-field magnetization curves at $\text{T = 4.2}\text{K}\text{(}\text{T}\text{T}{}_{\mathrm{c}}\text{? 2.3)}$. The $\text{T}{}_{\mathrm{c}}\text{θ}$ values obtained point to the presence of further neighbour interactions considerably stronger than previously assumed. The effective number of equivalently interacting magnetic neighbours is estimated to be at least seventeen.     

Magnetic ordering in (La,Gd) Al2 alloys

The detailed dependence of the magnetic ordering temperature θ on Gd concentration n below ～ 15 at.% Gd substitution for La is reported for the system ($\text{La}$Gd) Al₂. In this concentration range, the θ vs.n curve lies markedly below the extrapolation of the linear behavior previously observed for concentrations ? 20 at.% Gd, and apparantely goes to zero at a finite concentration. The effective moment of Gd is enhanced by 1 μ_B over the free ion value.     

Optical spectroscopy in semiconductors in high magnetic fields using polarization modulation

Differential magneto-reflection spectra in the 1.8 to 5 eV energy range are presented for GaP, Ge, GaAs, InSb, and Si. These spectra were obtained using polarization-modulated light from [111] faces of samples in the Faraday configuration. In medium strength magnetic fields, the results are similar to those obtained using other techniques, such as electric field modulation and wavelength derivative spectroscopy in the same energy range. In higher magnetic fields (B of 50 kG or larger) more detailed structure is resolved. Oscillations attributed to Landau level transitions have been seen at critical points in the visible in InSb and in GaSb in fields up to 100 kG. At the E₁ edge an unexpected anomaly has been observed in InSb. Within experimental error, the Landau levels are equally spaced for n < 5 and n > 5 but at n = 5 there is an abrupt change in the cyclotron energy. Here n is the usual magnetic quantum number. The transverse masses are measured as $\text{m}\text{μ}{}_1\text{= 18.9 ± 0.9 (n < 5)}$, and $\text{m}\text{μ}{}_2\text{= 16.0 ± 0.9 (n > 5)}$. Possible causes of this effect are discussed. In GaSb at the corresponding threshold. Landau level observations give a mass value of $\text{m}\text{μt}\text{= 21.4 ± 1.5}$.     

Superparamagnetic-like behaviour of magnetic alloys

The effect of antiferromagnetic interaction on a binary Ising ferromagnetic alloy A_pB_1?p is studied based on cluster-variational method and assuming either J_AB or J_BB or both exchange interactions to be of antiferromagnetic type. In a ferromagnetic state the moment saturates to a value much lower than its full value. Within the temperature interval where moment saturates, the system exhibits superparamagnetic-like behaviour. The induced moment becomes a function of $\text{h}\text{T}$ only, and the zero-field susceptibility follows Curie law. The incomplete saturation of moment persists up to a large value of $\text{h}\text{T}$. The short-range order parameter at T = 0 is much less than that of homogeneous ferromagnet.     

Theorie semimicroscopique des solutions solides Cr1−xVxN

The solid solutions Cr_1?xV_xN show at low temperatures a progressive establishment of an orthorhombic distorsion and an antiferromagnetic order (of the fourth kind) for $\text{x <}\text{1}\text{3}$ accompagnied by a (cubic) fraction which remains disordered at the lowest temperatures : No ordering occurs for $\text{x >}\text{1}\text{3}$. Assuming a Gaussian distribution of local concentrations in otherwise homogeneous cells (cellular model), the mean magnetic moment, measured by neutron diffraction can be related to a constant moment of Cr provided the local vanadium concentration is smaller than 0.26. The cell size contains 20 metal atoms.     

Long range interactions and spin wave excitations in FexPd82−xSi18 metallic glasses

The low temperature magnetization of amorphous Fe_xPd_82?xSi₁₈, 2 ? x ? 25, approaches saturation like 1/H. RKKY-type cluster-cluster interactions and single impurity effects are indicated. The effective strength of the RKKY interaction decreases with increasing x. The magnetization of both spin glass-like and weakly ferromagnetic alloys exhibits Bloch's T^{$\text{3}\text{2}$} dependence. The spin wave stiffness constants increase linearly with 2 ? x ? 25. The range of exchange interactions decreases with increasing x.     

A comparative study of FMR and Brillouin light scattering on amorphous Fe40Ni40B20

It is shown that magnetic surface mode frequencies in the amorphous ferromagnet Fe₄₀Ni₄₀B₂₀ measured using Brillouin light scattering depend upon the incident laser light intensity: presumably due to local heating of the specimen due to the concentration of the light flux into a focal spot only a few microns in diameter. Surface mode frequencies extrapolated to zero light intensity are shown to be consistent with magnetic parameters measured using ferromagnetic resonance at 35.731 GHz to within ±0.5 GHz for specimens of amorphous Fe₄₀Ni₄₀B₂₀. 0.5 GHz corresponds to a change of 0.17 kG in the saturation magnetization, 4πM_s.     

Study of the local susceptibility in the Fe: Au system

Mössbauer effect measurements of the Fe: $\text{Au}$ system are reported which yield the local susceptibility of the Fe ions. At high temperatures (T ? 10°K) a Curie Weiss law with θ₁ = 9.8°K is observed, whereas at low temperatures the Curie Weiss temperature is θ₂ = 0.45°K. In both temperature regimes the local susceptibility is a linear function of the total susceptibility. In addition below 4°K the local magnetization is a linear function of the total magnetization up to external fields of 60 kG.     

Magnetic structure of BaCaFe4O8-analysis of neutron diffraction measurements

The compound BaCaFe₄O₈ crystallizes in the trigonal space group P$\text{31}$m with one formula unit per unit cell with lattice constants $\text{a = 5.4059}\text{A}$ and $\text{c = 7.7023}\text{A}$ Neutron diffraction measurements carried out on a powder sample over the temperature range 300–900 K showed that the compound undergoes a magnetic transition to an antiferromagnetic state at a Néel temperature T_N = 680 ± 5 K. Analysis of the room temperature neutron diffraction pattern gave a magnetic unit cell that has the same periodicty as the crystallographic one. An antiferromagnetic model is proposed with the iron spin magnetic moments parallel to the c-axis of the unit cell. The magnetic moment of the Fe³⁺ ion was found to be (4.5 ± 0.1)μ_B