NiMnSb half-Heusler alloy in the form of a rod has been prepared by rapid quenching (suction-casting) method. The rod is characterized by single phase C1_b crystalline structure with lattice parameter a=5.982 Å. Magnetic measurements reveal an isotropic character of bulk NiMnSb alloy. Our study shows relatively high spin polarization of bulk NiMnSb in the range 35-50%.
The magnetic properties of (U_{1-x}Dy_{x})Ni_{5} compounds were studied in the temperature range 2-800 K and fields up to 7 T. The compounds having x ≥ 0.2 are magnetically ordered. Above the Curie points, the reciprocal susceptibilities follow a modified Curie-Weiss behaviour. UNi_{5} is a paramagnet. A peak in the temperature dependence of the magnetic susceptibility is evidenced at T ≈ 20 K. For T > 140 K the UNi_{5} susceptibility is temperature independent.
We report on the basic magnetic properties of glass-coated Co_2MnSi Heusler microwires. Measurements of hysteresis loops in different directions show that easy magnetization axis coincides with the wire's axis. The frequency dependence of the coercive field has been measured at room temperature in the frequency range from 10 Hz to 10 kHz. The coercivity decreases with the frequency up to 100 Hz and then increases linearly up to 1 kHz.
In the present study SQUID magnetic and ^{57}Fe Mössbauer measurements were performed on bulk Co₂FeAl_{1-x}Siₓ, Co₂Fe_{0.9}TM_{0.1}Si (TM = Ti, V, Cr, Mn, Co, Ni, Cu), Co_{2-y}Fe_{1+y}Si and Co₂Fe_{1+z}Si_{1-z} samples prepared by induction melting. The Co₂FeAl_{1-x}Siₓ shows the L2₁ crystal structure only for x ≥ 0.5, between x = 0 and 0.3 it has the B2 structure (Fe-Al, Si disorder). The average magnetization of these alloys does not follow the expected Slater-Pauling trend (on the Si side saturation is observed around 5.75 μ_{B}/f.u.) and similar deviation is observed for the replacement of Fe by transition metal (TM) atom. The effect of the antisite disorder (Fe-Si) on the magnetization and Fe hyperfine parameters was determined and significant decrease in the Co magnetic moment for excess Si neighbourhood is extrapolated. The formerly reported large ≈ 6 μ_{B}/f.u. magnetization for Co₂FeSi was observed only in samples having Fe excess and Si deficiency.
This report focuses on magnetoelastic properties and critical behaviour of (Fe_{1-x}Ni_{x})_{2}P system. For low Ni content (x=0.01) an isolated critical point was found. Analysis of this critical behaviour in the frame of molecular field approximation was carried out. Moreover, thermal variations of the lattice parameters, as measured by X-ray diffraction techniques, were studied. The (P,T) phase diagrams obtained for several Ni contents show the evidence that the Curie temperature decreases with pressure. The Mössbauer spectra collected for x = 0.025, 0.1, 0.2, 0.25 at different temperatures are also analysed. The existence of two nonequivalent crystallographic sites occupied by iron atoms as well as local magnetic structure is discussed.
Transverse magnetoresistivity (H ∥ [001]; and current ∥ [110]) of U_{3}As_{4} has been measured in field up to 35 T. An abrupt change of the magnetoresistivity behaviour from saturated (low field) to unsaturated (high field) type was observed at the spin reorientational transition (19.1 T at 4.2 K). The transition is accompanied by a peak in the magnetoresistivity. The behaviour is ascribed to fractional spin polarization of the band electrons.
The crystal structure of CrTe suggests two-dimensional magnetism in the plane perpendicular to the c axis. It is consistent with the temperature dependence of the g factor and EPR lines width observed. In the present paper we investigate the CrTe alloy which has been prepared by melting of the powdered Cr₂Te₃ in evacuated quartz ampoule at the temperature 1600 K. ESR spectra were recorded using X-band (9.4 GHz) spectrometer provided with gas nitrogen cryostat. The shape of the EPR line depends strongly on the temperature. In the vicinity of the room temperature the lines become very wide and weak or disappear completely. At lower temperatures the shape of the lines approaches the Dyson function. The asymmetry of lines is attributed to the strong exchange interactions as well as to the semimetal electrical conductivity. Above the room temperature the shape of spectra is characteristic for the paramagnetic phase. Results were addressed based on the model of critical spin fluctuations in two-dimensional Heisenberg magnet proposed by Eremin et al.
Soft/hard magnetic bilayers are attractive systems for investigating their physical behavior due to scientific curiosity and the potential for technological applications. Thus, 10 nm thick hard magnetic layer placed on a 20 nm soft magnetic layer was modeled in this work. After the constructing of magnetic thin films, the bilayer structure was simulated based on micro-magnetic modeling. When constructing the Hamiltonian of the system, magnetocrystalline anisotropy term was also under debate with classical Zeeman and exchange terms. Energy minimization in the simulation was performed using Metropolis algorithm and Markov Chain Monte Carlo (MC-MC) method. As a result of modeling, hysteresis curves, remanent magnetization and coercive fields were obtained at different temperatures.
Electromagnetic waves generated by the Heusler alloy Ni_{2.14}Mn_{0.81}GaFe_{0.05} at structural phase transition was detected in the frequency range of 28-32 GHz. Influence of the kinetics of phase transitions on the nature of the sample millimeter radiation was studied as well. It has been observed that the contribution of the intrinsic radiation increases with increasing of the heating/cooling rate. The possible mechanisms and theory of such effect is discussed. It is shown that the maximum radiation intensity should be emitted in direction perpendicular to the movement of interphase boundary.
One-particle electronic states of ferromagnetic single crystal Laves phase GdAl_{2} is calculated with the help of augmented spherical waves, based on density functional theory. Density of states, partial densities of states are presented. The behavior of the spectrum in the vicinity of the Fermi energy and the number of occupied states are discussed in detail.
We focused on the interaction between two ferromagnetic cobalt layers through a non-magnetic titanium layer. The magnetic properties of the structure were characterized by ferromagnetic resonance technique. The data were collected as a function of non-magnetic titanium layer thickness. Co/Ti multilayer (Ti(50 Å)/Co(45 Å)/Ti(2-40 Å)/Co(40 Å)/Ti(100 Å)) films were grown onto naturally oxidized p-type single crystal Si (100) substrate at UHV condition with magnetron sputtering system at room temperature. The thickness of Ti spacer layer ranges from 2 to 40 Å with 2 Å steps. We did not observe usual optic and acoustic modes; instead we had two broad overlapped peaks for the films ranged from 6 Å to 40 Å. One interesting result was the high anisotropic resonance field values for these films. Exchange coupling between ferromagnetic layers causes shift on resonance field values but these shifts in our samples were much larger than expected. This large anisotropic behavior is not clear at the moment. Our theoretical model was not able to determine a value for the exchange coupling parameter. One reason can be the close thickness values for Co sublayers. The other reason can be the Ti non-magnetic layer. If titanium did not grow layer by layer on cobalt, the cobalt ferromagnetic layers may behave as a single layer. As a result one cannot observe exchange interaction between ferromagnetic layers through non-magnetic spacer.
The magnetic properties of Co-Ni compounds with MnCu_{2}Al or MgAgAs-type structure (the Heusler phases) were studied. Paramagnetic, ferromagnetic moments, Curie's temperature increase with Co content. The ratio of ordered to paramagnetic moment varies with the Curie temperature following itinerant ferromagnetism models. A metal-insulator transition occurs in the TiCo_{x}Ni_{1-x}Sn series, which causes a more rapid drop of the Curie temperature than in TiCo_{x}Ni_{2-x}Sn solid solutions which remain metallic.
A polycrystalline sample of CeOsGa₄ was prepared by arc-melting stoichiometric quantities of high purity elements of 4N and greater, in an arc furnace. The data was confirmed to crystallize in an orthorhombic structure, with a space group Pmma (Number 51). Measurements of the magnetic susceptibility showed a distinct anomaly around T_{o} = 3.8 K, while the high temperature data (above 100 K) obeys Curie-Weiss law. The calculated effective moment of 2.44 μ_{B}, was obtained, which was a bit less than the theoretical moment for a Ce³⁺ ion of 2.54 μ_{B}. Magnetization data at T=2 K depicts that CeOsGa₄ does not saturate up to applied magnetic field of 7 T, while the data measured at 9 K indicates that the compound is purely paramagnetic at that temperature. The low temperature specific heat data is characterized by an anomaly at T_{o} = 3.8 K confirming the χ(T) data. Electrical resistivity shows a metallic behaviour at high temperatures with a deviation at low temperatures, signalling the cooperative behaviour which results to ordering. In this work we present the initial studies of the physical properties measurements performed on this compound.
We report on structural and magnetic properties of Ni_{50}Mn_{50-x}Sn_x (x=12÷14) films and compare them with those of the bulk Ni-Mn-Sn alloys. Magnetic measurements reveal clear presence of martensitic transformation in bulk alloys but in the flash-evaporated Ni-Mn-Sn thin films martensitic transformation is usually less visible. The best film samples annealed for 1 h at about 900 K exhibit clear signs of martensitic transformation: i.e., a small defect in magnetization and a substantial increase in ferromagnetic resonance line width.
We investigated the effect of large compressive stress on magnetic shape memory effect in modulated 10M martensite of Ni-Mn-Ga Heusler alloy. The single crystalline sample deformed approximately elastically up to highest load 540 MPa. Structural and microstructural changes of a single crystal were analysed by X-ray diffraction 2D scan mapping in 2θ and ω. Although the crystal structure, lattice cell parameters, and twinned microstructure (a/b and modulation twinning) exhibited only small changes after the loading, the volume of the sample undergoing the magnetically induced reorientation decreased sharply while magnetic field necessary for the reorientation gradually increased. The extrapolation suggested that no magnetically induced reorientation might occur after compression of about 1 GPa.
Transition metal chalcogenides of a zinc-blende structure are theoretically predicted to be half metallic and, therefore, they are interesting for spintronic applications. However, the ground state of these compounds is hexagonal, of NiAs type, whereas the cubic phase is a metastable one. Here, we investigate the Cr-Te bondings of both phases of Cr-Te from point of view of symmetry. The hybridization in octahedral and tetrahedral lattice is studied for both structures. The fiber bundle presentation of the hybridization problem is also addressed.
Co/Cu multilayers having different bilayer number (total thickness) were electrodeposited on polycrystalline Cu substrates with a strong [100] texture from an electrolyte including Co and Cu ions under potentiostatic control. The structural data from X-ray diffraction (XRD) revealed that all films have face-centered cubic (fcc) structure, but their crystal textures change from [100] to [111] as the bilayer number increases. The magnetic analysis by vibrating sample magnetometer (VSM) showed that the magnetic moment per volume decreases as the bilayer number increases. Magnetoresistance (MR) measurements were made at room temperature in the magnetic fields of ± 12 kOe using the Van der Pauw (VDP) method with four probes. The samples with the bilayer number less than 111 exhibited giant magnetoresistance (GMR) with a negligible amount of anisotropic magnetoresistance (AMR), while the ones with the bilayer number larger than 111 have pure GMR effect.
We investigate the effect of the electronic and magnetic properties on nonmagnetic Cu-3d atoms doping the Heusler alloy Ti_2Ni_{1-x}Cu_xAl (0 ≤ x ≤ 1) using first-principles calculations. The optimized lattice constants are consistent with the Vegard law, and energies of doped systems become more lower as the increase of x concentration. A critical transition diagram from half-metallic to metallic characters is discussed. In addition, the magnetic interactions between p and d states are illustrated. Finally, magnetic moments are given as a function of x value, which implies that the Slater-Pauling rule is obeyed at low Cu content (x ≤ 0.2).
A newly developed pressure setup for a.c. susceptibility measurements in the pressure range up to 2.0 GPa is presented; the temperature domain extends from 77 to 450 K. The steel pressure chamber contains the sample located at the center of a set of three compensated pick-up coils and the pressure and temperature sensors. Either alcohol or extraction naphtha is used as the liquid pressure transmitting medium. The (P,T) magnetic phase diagram of (Fe_{0.975}Ni_{0.025})_{2}P system in the pressure range up to 2.0 GPa is reported.
Soft magnetic composite materials play an important role in nowadays industry, replacing the traditional materials such as electrical steels and soft ferrites, especially at medium and higher frequency applications. The material can be tailored for a specific application by changing the composition of the material and by adaptation of the fabrication process. The aim of this work was to investigate the morphology, phase composition and magnetic properties of soft magnetic composite materials with various magnetic content to minimize the total magnetic losses. The prepared sample series was based on the mixture of two different ferromagnets Vitrovac 6155 and Somaloy 700 without addition of insulating material. The samples were prepared by conventional powder metallurgy with particular fraction of Vitrovac in the form of a ring for magnetic measurements in AC fields and electric resistivity measurements. The samples with 5 wt% and 20 wt% fractions of Vitrovac exhibit lower values of total losses in comparison with Somaloy heat treated at 530°C.
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