Magnetic susceptibility of dilute magnetic alloys

The magnetic susceptibility of dilute magnetic alloys is calculated using the Nagoaka approximation to the Kondo problem. We use the exact solutions of the Nagaoka equations, or equivalently Suhl's dispersion relations, as obtained recently. Our result is represented by a universal function of a certain temperature parameter. In the case of ferromagnetic coupling no appreciable change of the free spin susceptibility is found over the whole temperature range. In the case of antiferromagnetic coupling we find that the free spin susceptibility is greatly reduced. In fact, for spin 1/2, the result indicates the breakdown of the expansion in terms of the impurity concentration and suggests the onset of impurity ferromagnetism.     

Magnetic susceptibility measurements of dilute MgEu alloys

Magnetic susceptibility measurements of strain-free dilute alloys of Eu in Mg indicate that the Eu is predominantly divalent with ${}^8\text{S}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ ground state. The analysis indicates no solid solubility of Eu in Mg.     

Magnetic breakdown in very dilute aluminum-silver alloys

The temperature and magnetic field dependences of the electrical magnetoresistance of very dilute (1 300 ? RRR ? 10 000) AlAg alloys have been measured for H ? [110]. Although no oscillations were observed, there is evidence in the temperature dependence of the magnetoresistance for the existence of magnetic breakdown.     

Transport properties of dilute magnetic alloys

The electrical resistivity, thermopower, and the electronic part of the thermal resistivity of dilute magnetic alloys are calculated in the framework of the Suhl-Nagoaka theory. Using Bloomfield's and Hamann's solution of the Nagaoka equations, we derive expressions for the transport quantities in the limitT? ¯ T_K andT?¯ T_K to order (In ¯T _K /T)^?4 where ¯T _K is the Kondo temperature which may depend on the spin independent scattering. We find that the thermopower and deviations from the Wiedemann-Franz law in this limit decrease as ¦In ¯T_K/T¦^?3 if one neglects a trivial temperature dependence of the thermopower due to the electron-phonon interaction.     

Magnetic ordering of localized spins in dilute alloys

The interaction of electrons with the ordered magnetic impurity system was shown to lead to great electron spectrum renormalization. Thus the effective mass on the Fermi surface becomes several times as large. For the addition to the effective mass the concentration and temperature dependences are obtained which are in good agreement with the experimental ones.     

Magnetic phase diagram of very dilute Pd-based alloys

The magnetic phase diagram of Pd-based 3d metal alloys is calculated on the basis of the random molecular field model. A paramagnetic-spin glass transition is expected for c < 0.06 at %, a paramagnetic-ferromagnetic one for c > 0.17 at %, while in the intermediate region a paramagnetic-ferromagnetic-spin glass transition is predicted.     

Magnetic susceptibility of dilute Al-Dy alloys at high temperatures

The magnetic susceptibility of Al-Dy alloys with the dysprosium content from 0.1 to 2.0 at % in the temperature range 300–1850 K has been studied. It is established for all compositions that the susceptibility begins to increase when the alloy temperature exceeds the melting temperature of the Al₂Dy compound, and the concentration curves exhibit oscillations of the same type in the solid and liquid states. The experimental results are interpreted in terms of the existence of chains composed of Al₂Dy quasi-molecules in the alloys.     

Magnetic properties of Cr-Fe-Mn alloys

The magnetic behaviour of a Cr_80−xFe₂₀Mn_x alloy system with x=2, 7, 10, 13 and 22 has been investigated in the temperature range 2-400 K through measurements of magnetization, electrical resistivity, magnetoresistivity, specific heat and thermal expansion. The temperature vs. Mn concentration magnetic phase diagram of the system is rich in magnetic behaviour with ferromagnetic (FM), antiferromagnetic (AFM) and paramagnetic phase regions and a spin-glass (SG) region at the lowest temperatures. Phase transition temperatures amongst these different magnetic phases could be identified from well-defined anomalies of magnetic origin that are displayed by graphs of the above-mentioned physical properties as a function of temperature. The time relaxation of the thermoremanent, isothermal remanent and field-cooled magnetizations below and above the SG freezing temperature show unusual aspects. These relaxations do not follow the usual superposition principle that is expected for typical SG materials. Negative giant magetoresistance (GMR) is observed in the alloys at 4 K. The GMR initially increases sharply on increasing the Mn content in the alloy system, followed by a tendency towards a saturation negative value for concentrations of more than about 10 at% Mn. Low-temperature plots of C_p/T vs. T², where C_p is the specific heat, present anomalous behaviour for alloys with x=2, 10 and 22. For x=2 the plot shows an upturn at the lowest temperatures that changes over to a prominent downturn for x=10 and 22. This behaviour is attributed to Fe concentration fluctuations in the alloys, confirming the theoretical model of Matthews.     

Magnetic properties of amorphous alloys

The magnetic properties of existing amorphous iron based materials, i.e., Fe--metalloid, Fe--early transition metals and Fe--rare earth alloys, are briefly discussed for some representative alloys. The spin orientation of amorphous Fe--metalloid alloys has been determined by the angular dependence of hyperfine interactions. It is shown that in iron--early transition metals ferromagnetic order is not long-ranged, but determined by magnetic clusters. The magnetic hyperfine field distributions of Fe-rich iron--early transition metals consist of a high and a low field tail. The magnetic structure has been investigated for two representative Fe--RE (RE = Er, Ce) amorphous alloys. For the first time, the magnetic coupling phenomenon in amorphous/crystalline multilayers has been discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetic properties of CuRh alloys

By means of rapid quenching techniques single phased samples of Cu_xRh_1?x(0?x?1) were obtained. For these alloys the Knight shift of ⁶³Cu and ¹⁰³Rh has been determined employing pulsed NMR at low temperatures, furthermore the magnetic susceptibility was measured for temperatures between 4.2 and 300 K. While the Knight shift of ¹⁰³Rh is dominated by s-electron contributions in spite of a high density of d-states at the Fermi level, for the susceptibility, however, the d-electron contributions prevail. In addition the susceptibility shows a pronounced maximum at about 10 at.% Cu. Using the extrapolated Knight shift of copper (x→0) we estimate a net copper hyperfine field of — 15 T in close agreement with the corresponding values for CuPd and CuPt.     

Magnetic properties of electrodeposited iron-nickel alloys

The basic magnetic properties, viz., magnetic saturation and coercive force, have been established by measurement of about 150 specimens for electrodeposited iron-nickel alloys over the entire range of chemical compositions. The magnetization data were related ot the physicochemical aspects of the electrodeposition process.     

Magnetic properties of metastable Gd-Cr alloys

We report on the magnetization, magnetocaloric effect, magnetic ordering temperatures, saturation magnetic moments and anisotropy of sputter-deposited Gd_xCr_1−x alloys with Gd atomic concentrations, x, ranging from 0.13 to 0.52. The complex magnetic nature of the Gd-Cr films was revealed from the M×H isotherms, which do not show saturation even at an applied field of 70 kOe and a temperature of 2 K and do not exhibit a linear behavior at higher temperatures. For some of the samples, the isotherms were used to determine the isothermal entropy variation as a function of temperature, for a change of 50 kOe in the applied magnetic field. The saturation magnetic moment varies with x and follows the dilution law, implying that the Cr atoms do not contribute to the total moment of the Gd-Cr alloys. Both static magnetization and dynamic susceptibility measurements reveal the existence of a magnetic glassy behavior in the alloys, which occurs below a freezing temperature. The existence of anisotropy at low temperatures for all samples was revealed by their M×H hysteresis loops from which the in-plane coercive fields, H_c, were determined. A monotonical increase in H_c with increasing Gd concentration was observed.     

Magnetic properties of amorphous NiP alloys

Magnetization, NMR and coercive force measurements were performed on amorphous Ni_1?cP_c alloys for concentration ranging between 0.15 and 0.25. The experimental results show that the magnetism is not of the same nature below and above some critical concentration c₀ which determines the concentration ranges: the first one (0.15 < c < 0.18) presents the characters of a weak homogeneous ferromagnetism, while inhomogeneities dominate the magnetic properties of the second one (0.18 < c < 0.25).     

Magnetic susceptibility and electrical resistivity of dilute liquid copper - iron alloys

Electrical resistivity and magnetic susceptibility measurements on dilute liquid CuFe alloys are reported. Small additions of Fe increase the resistivity of liquid Cu in a drastic manner, whereas the temperature coefficient is found to be decreased. Due to the localized magnetic moments of the impurity atoms the diamagnetism of Cu is converted into a strong temperature-dependent paramagnetism indicating about 3.5 unpaired d electrons per Fe atom. The electronic properties of CuFe resemble those of liquid CuMn and AuFe which, in the solid state, are known for their Kondo-like behaviour. The experimental findings are tentatively interpreted in terms of spin-disorder scattering with special emphasis on the negative temperature coefficient of the impurity resistivity.     

Magnetic field dependence of the impurity specific heat in dilute magnetic alloys

Using a trial sunction scheme at finite temperature, the impurity specific heat has been calculated in terms of the Wolff model with an external magnetic field. When local moments exist, the magnetic field effect is drastic under accessible experimental condition. In the absence of local moments, the specific heat is practically field independent. If accurate specific heat can be measured, it provides a new method to detect local moments in dilute magnetic alloys.     

Magnetic properties of dilute Co impurities in liquid Sn

The susceptibility of dilute Co impurities in liquid Sn is reported. It displays an almost linear increase from 1.8 × 10^?4 cm³/mole at 240°C to 4.5 × 10^?4 cm³/mole at 1000°C. These results are compared with other experimental information and are shown to be consistent with a recently proposed ionic impurity model if an interaction parameter is assumed to be temperature dependent.     

Magnetic and structural properties of FeCr alloys

Synergistic synchrotron x-ray absorption experiments using imaging magnetic microspectroscopy, x-ray magnetic circular dichroism, and ab initio calculations on FeCr alloys reveal that the Cr content strongly influences the ferromagnetic microstructure and the Fe magnetic moments. The Cr local structure resolved by extended x-ray absorption fine structure (EXAFS) is also found to be affected by the alloy's composition. Both EXAFS and ab initio calculations show a change in the Cr local atomic structure above 10 at.% Cr content from the distance contraction of the first two coordination shells around the Cr absorbing atom. These results indicate the strong dependence of magnetic and structural properties of these alloys on Cr concentration.     

Magnetic properties of 36 wt% Ni-Fe alloys

This paper reports the effect of adding molybdenum, chromium or copper, in amounts up to 5 wt%, on the initial permeability μ_i, magnetostriction constant λ_ps and saturation magnetisation M_s of a 36 wt% Ni-Fe alloy. Mo and Cr decrease λ_ps and M_s, but Cu has the opposite effect. The initial permeability is increased by Mo and Cr additions, except at high concentrations, whereas Cu produces little change in μ_i. Changes in the magnetic moment per atom are discussed in terms of the effect of alloying on the mean number of (d+s) outer electrons. It is suggested that the change in magnetic moment per atom may influence the value of μ_i indirectly due to changes in the spin-orbit and exchange interactions, which alter the anisotropy and magnetostriction constants and domain wall energy.     

Magnetic properties of CrPd alloys

Magnetic susceptibility, resistivity, and neutron diffraction measurements have been obtained for a series of CrPd alloys containing up to 3 at.% Pd. The Néel temperature variation is irregular for a solute which is to the right of Cr in the periodic table.