The dependence of bilinear and biquadratic interlayer coupling on the thickness of magnetic films is analysed for a trilayer structure with specular reflection at the outer surfaces. It is shown that the oscillation periods corresponding to the case where the thickness of one of the two magnetic films is constant, while that of the second one is varied, can be different from the oscillation periods in the case where the thicknesses of both magnetic films vary simultaneously. The nonoscillatory component of the coupling parameter is shown to be weakly dependent on the thickness of the magnetic films.
We report the discovery of new effect in La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} - the jump of magnetization induced by external electric field E (2.5-4)V/cm at a given magnetic field H (18-25) kOe at T=4.2 K. This effect is large when compared with a metamagnetic transition induced by the magnetic field in many substances. The origin of the magnetization jump induced by external electric field has not yet been explained. We assume that this transition is induced by the hopping of E-excited e_{g} electrons and that this is a source of a jumpwise increase in magnetization in the non-collinear magnetic phase within the perovskite. This effect can be attributed to a strong coupling between carriers induced by the electric field (the conduction electrons e_{g}), and the local magnetic moments (t_{2g}-localized spins) through a mechanism of the Zener double exchange.
Mixed-metal complex consisting of ruthenium(II,III) pivalate, ([Ru₂(piv)₄]⁺) (Hpiv = pivalic acid), tetraethylammonium and octacyanidotungstate(V) ions, (Et₄N)[{Ru₂(piv)₄}₂W(CN)₈]·4H₂O, was synthesized and characterized by elemental analysis, infrared and UV-vis spectra and temperature dependence of magnetic susceptibilities (2-300 K). The magnetic susceptibilities, zero-field-cooled and field-cooled magnetizations, and AC susceptibility data showed that the present complex is ferrimagnetic with T_{c} value of 80 K. The field dependence of magnetization exhibited a hysteresis with a coercive field of 17000 Oe at 5 K.
The magnetization and magnetic susceptibility of Bridgman-grown Sn_{1-x}Gd_{x}Te with values of x up to 0.09 have been measured over a temperature range from 2 to 300 K and in magnetic fields up to 5.5 T. The magnetic susceptibility data followed the Curie-Weiss relation with a small Curie temperature that indicated a weak antiferromagnetic coupling among Gd ions. The magnetic field dependence of the magnetization was fitted to a modified Brillouin function with parameter values that agreed fairly well with those from Curie-Weiss plots. The value of the exchange parameter was larger than in Pb_{1-x}Gd_{x}Te. The samples were p-type with carrier concentrations up to 1.3 x 10^{21} cm^{-3}. The ferromagnetic or spin-glass phase due to the RKKY interaction was not observed.
The effect of a replacing La by Ce in Gd_{0.9}La_{0.1}Cu_{6} was investigated by ESR method. It was found that cerium ions cause an increase in the conduction electron relaxation to the lattice and change the conduction electron band structure.
Antiferromagnetic interlayer exchange coupling in semiconductor EuS-PbS-EuS ferromagnetic trilayers grown on PbS (001) substrates with ultrathin (0.6-1.2 nm) nonmagnetic PbS spacers is studied by SQUID magnetometry and model calculations. Analysis of the experimentally observed magnetic field and temperature dependence of the magnetization of EuS-PbS structures reveals a rapid decrease in the interlayer coupling energy with increasing temperature indicating a temperature dependence of the microscopic coupling mechanism acting in these all-semiconductor ferromagnetic/nonmagnetic multilayers.
The individual Co site contributions to the magnetocrystalline anisotropy in RCo_{5}, RCo_{4}B and R_{3}Co_{11}B_{4} compounds have been studied. An analysis is given of the room temperature anisotropy constants of these compounds by using a model of Streever. The values of the rare earth-transition metal exchange coupling J_{RCo}/k_{B} derived by mean field analysis of the Curie temperatures are -11.2 K, -15 K and -20.9 K, respectively. In general, a decrease in J_{RCo}/k_{B} with increasing Co concentration is observed.
Antiferromagnetic interlayer coupling between ferromagnetic layers of EuS via nonmagnetic PbS spacer layer was experimentally studied in EuS-PbS wedge multilayers grown on KCl (001) substrates with EuS thickness of 6 nm and PbS thickness varying in the wedges in the range 0.3-6 nm (i.e. n=1-20 monolayers). Measurements of magnetic hysteresis loops of EuS-PbS multilayers performed in the temperature range 5-30 K by superconducting (SQUID) and magneto-optical magnetometers revealed a rapid increase in saturation magnetic field in multilayers with PbS spacer thinner than about 1.5 nm. It shows a monotonic increase in interlayer coupling strength with a decreasing PbS spacer thickness, in qualitative agreement with 1/2^n dependence predicted theoretically for semiconductor magnetic superlattices.
Electric conductivity, Hall effect and magnetic susceptibility of Pb_{1-x-y} Sn_{y}Gd_{x}Te mixed crystals with 0.13 ≤ y ≤ 0.93 and 0.001 ≤ x ≤ 0.04 were experimentally studied over the temperature range 4K ≤ T ≤ 300 K. The incorporation of Gd ions into the Pb_{1-y}Sn_{y}Te matrix results in semi-metallic n-type conductivity of the crystals with y < 0.6. For crystals with y > 0.6 one observes only semi-metallic p-type conductivity. We present a model explaining these results in terms of the Sn composition dependence of the location of Gd^{2+/3+} level with respect to the band edges of PbSnGdTe.
Magnetic, transport and structural properties of bulk crystals of Sn_{1-x}Gd_{x}Te with Gd content 0.002 < x < 0.09 and varying carrier concentrations obtained by an isothermal annealing were studied in the temperature range T = 1.5 - 80 K. We found the effect of resonant increase in antiferromagnetic spin-spin exchange interactions in the crystals with 0.025 ≤ x ≤ 0.05. No effect was found in crystals either with higher (x > 0.05) or with lower (x < 0.025) Gd concentration. The observed Gd composition dependence of the magnetic and transport properties of SnGdTe can be explained in a proposed model relating these experimental properties to the Gd composition induced shift of the position of Gd^{3+/2+} level with respect to the top of the valence band of SnGdTe.
Magnetic properties of semiconductor EuS(t)-PbS(d)-EuS(t) ferromagnetic trilayers (t=30÷300Å and d=7.5÷70Å) grown on n-type monocrystalline PbS (100) substrate were studied by SQUID magnetometry and ferromagnetic resonance technique yielding, in particular, the dependence of the ferromagnetic Curie temperature on the thickness of the EuS layer. Structural parameters of layers were examined by X-ray powder diffraction analysis. A high structural quality of the substrate and the multilayer was verified by the measurements of the X-ray rocking curve width indicating the values of the order of 100 arcsec and by atomic force microscopy revealing the presence on the cleft PbS surface regions practically flat in the atomic scale over the area of 1×0.1μm^2.
The influence of boron atoms on the magnetic properties of Νd(Co_{1-x}B_{x})_{5} (i.e. ΝdCo_{5}, NdCo_{4}B, Νd_{3}Co_{11}Β_{4} and Νd_{2}Co_{7}Β_{3}) compounds has been studied. These structures are based on the well-known CaCu_{5} structure. They all have the hexagonal symmetry and belong to the space group of P6/mmm. The experimental values of the Curie temperatures (T_{c}) of Nd(Co_{1-x}B_{x})_{5} are used to calculate the effective intersublattice exchange interactions (J_{NdCO}) between Nd and Co sublattices. As the Β content increases, a tendency to decrease in J_{NdCO} and T_{c} is found. This variation is compared with that observed for the Co magnetic moment.
The specific heat of (Cd_{1-x-y}Zn_{y}Mn_{x})_{3}As_{2} with low Mn concentration (x ≤ 0.067) and for two Zn contents (y = 0.14 and y = 0.34) has been measured in the temperature range of 1.5-30 K. The magnetic contribution to the total specific heat has been analysed within our generalized pair approximation model which takes into account the complicated tetragonal crystal structure of Cd_{1-x-y}Zn_{y}Mn_{x})_{3}As_{2}. Assuming that the total Mn-Mn interaction strength is a sum of superexchange and the Bloembergen-Rowland exchange, we have obtained a very good agreement between our approach and experiment by using the analytical formulae with only two adjustable parameters, i.e. the first nearest-neighbour exchange constants for both mechanisms which appear to be strongly dependent on Zn content.
We studied experimentally and theoretically the magnetisation of the Co/Ti multilayers. The results showed that the magnetic moments on Co atoms located at the Co-Ti interface are strongly reduced. For d_{Ti}=0.35 nm the estimated effective non-magnetic Co thickness at the Co-Ti interface amounts ≈ 0.08 nm and ≈ 0.1 nm at 4 K and 295 K, respectively. We found a good agreement between experimentally determined and theoretically calculated magnetisations.
It is shown that the Co sublayers grow in the soft magnetic nanocrystalline phase up to a critical thickness d≈3 and 2.8 nm for Co/Ti and Co/Zr MLs, respectively. The rapid decrease in the interlayer exchange coupling could be explained by its strong damping due to formation of a non-magnetic quasi-amorphous Co-Ti and Co-Zr alloy layer at the interfaces. The nanocrystalline 2.2 nm-Co/2 nm-Ti ML shows a weak 90° coupling near the transition zone from ferromagnetic to zero coupling.
Magnetic susceptibility has been measured in Pb_{1-x-y}Sn_{y}Mn_{x}Se with x values up to 0.02 and y values up to 0.05. The measurements were carried out using a SQUID system over a temperature range from 5 to 250 K. The susceptibility followed the Curie-Weiss relation with a small paramagnetic Curie temperature that indicated a weak antiferromagnetic exchange interaction between Mn ions. We analyzed the results together with our previously published data on high-field magnetization in this material. A reasonable agreement of the exchange parameters obtained from the low-field susceptibility and high-field magnetization data was obtained.
The CsNiF_3 has been for long time studied as a prototype of quasi-1D planar ferromagnetic system. At very low temperature the studied system is insulator and therefore the magnetic exchange interactions should decay very rapidly. We treated the magnetic exchange coupling within the Heisenberg model for the nearest neighbor interaction between the anti-ferromagnetically coupled Ni-chains. The influence of up to the second-nearest neighbors on the ferromagnetic exchange coupling along the Ni-chains was determined. The exchange interactions were calculated for the experimental volume by the density functional theory, within the all-electron approach using the local density approximation for the exchange and correlation. The Néel temperature was calculated by means of the mean-field theory and by the random-phase approximation method.
The effect of disorder in magnetic layers, in the spacer, and at interfaces between them on periods, amplitudes, and phases of oscillations of interlayer exchange coupling in magnetic multilayers is studied theoretically on the ab initio level. We employ the spin-polarized surface Green function technique within the tight-binding linear muffin-tin orbital method and the Lloyd formulation of the interlayer exchange coupling. The coherent potential approximation is used to describe the effect of alloying. The calculations are significantly simplified by employing the vertex-cancellation theorem. Numerical results illustrating the effect of various kinds of disorder in the system on the properties of the interlayer exchange coupling are presented.
The electronic and magnetic properties as well as the applications of IV-VI semiconductors with rare earth ions of Eu and Yb are briefly discussed. The detailed analysis is presented of the recent experimental investigations of the magnetic and transport properties of IV-VI semimagnetic crystals with Gd. It concerns, in particular, the effect of Fermi level position controlled f-f exchange interaction between Gd ions in Sn_{1-x}Gd_{x}Te.
Analysing the d-d interaction in diluted magnetic semiconductor quantum structures, we used our generalized pair approximation which permits to take into account the real spatial distribution of the magnetic ions in diluted magnetic semiconductor layers close to the nonmagnetic quantum well. We subsequently applied our approach to calculate the Zeeman splittings in the CdTe/Cd_{1-x}Mn_{x}Te quantum structures with x=5 and 7.5% and we obtained a good agreement with the experimental results.
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