Dynamic magnetic properties of ferromagnetic and antiferromagnetic Heusler alloys

Inelastic neutron scattering measurements on a ferromagnetic Heusler alloy, Pd₂MnIn_1?xSn_x at the composition x = 0.75, have established the spin wave dispersion in the three principal symmetry directions. The results have been interpreted using a simple Heisenberg model in which the exchange constants are of long range, extending beyond 12 Å. The Curie temperature, spin wave stiffness constant and the thermal variation of the magnetisation, calculated using the derived exchange parameters are in close agreement with observation.Anomalies in the spin wave dispersion, which are also present to a lesser degree in Pd₂MnSn, have been interpreted as precursor effects associated with the onset of antiferromagnetic ordering, type AF3A, which is the magnetic structure observed in the range 0.2 ? x ? 0.6.     

Density of states and asphericity of electron distribution in ferromagnetic Co-Ni alloys

The coherent potential approximation has been extended in order to treat the case of multiple bands in ferromagnetic substitutional binary alloys. The concentration dependence of total magnetic moments and their aspherical contribution, e_g and t_2g, were derived and compared with experimental data in Co-Ni f.c.c. alloys.     

Peaks in low field a.c. susceptibility of ferromagnetic Heusler alloys

The observation of a peak in the low field susceptibility need not always be taken to imply spin glass type of freezing. It may also be the consequence of a rapid build up of anisotropy field below the ordering temperature. The results of low field a.c. susceptibility measurements on Ru and Rh based ferromagnetic Heusler alloys presented here substantiate the above statement.     

The radial dependence of the magnetic hyperfine field for Sn atoms in the ferromagnetic Heusler alloys

The magnetic hyperfine fields,B _hf, for impurity¹¹⁹Sn atoms in Z sites of ferromagnetic Heusler alloys Co₂MnZ (Z=Si, Ge) are measured by the Mössbauer effect. At 77 KB _hf=–1.43±0.04 T in Co₂MnSi andB _hf=+1.05±0.05 T in Co₂MnGe. From the comparison between the values ofB _hf for Sn atoms in Co₂MnZ (Z=Si, Ge, Sn), it follows that the negative contribution toB _hf drops as the interatomic distance begins to increase. This radial dependence also manifests itself in the anomalies of the temperature dependences of the hyperfine fields. The temperature anomaly is positive for Sn in Co₂MnGe and negative for Sn in Co₂MnSi.     

Electrical properties of ferromagnetic Ni2MnGa and Co2CrGa Heusler alloys

The electrical properties of ferromagnetic Ni₂MnGa and Co₂CrGa Heusler alloys are measured in the temperature range 4–900 K. The effect of the energy gap near the Fermi level in the electronic spectrum on the behavior of electrical resistivity and absolute differential thermopower is discussed.     

Electronic structure and magnetic, electrical and optical properties of ferromagnetic Heusler alloys

Measurements of the electrical resistivity and the Hall effect of the Heusler alloys NiMnSb, PtMnSb, CoMnSb, AuMnSb, CuMnSb and PtMnSn are reported. The anomalous Hall effect is analyzed in terms of the contributions from skew scattering and side jump. The spin polarization of the charge carriers is proportional to the magnetization. This is an indication that the electronic structure as a function of the temperature is best described by a local band model, with complete spin polarization of charge carriers parallel to the local magnetization at all temperatures. The spin disorder resistivity of NiMnSb is calculated with the local band model. The magneto-optical Kerr effect of PtMnSb is enhanced by the plasma resonance of the charge carriers.     

Laser-plasma deposited nanosized layers of ferromagnetic semiconductors and silicon- and germanium-based Heusler alloys

The electric, magnetic resonance, and magneto-optical properties of thin laser-plasma deposited 50–100-nm layers of diluted magnetic semiconductors Ge:(Mn, Al)/GaAs, Ge:(Mn, Al)/Si, and Heusler alloys Co₂MnSi/Si, Co₂MnSi/GaAs, and Fe₂CrSi/GaAs with T _c > 293 K were studied. Anomalous ferromagnetic resonance in Ge:(Mn, Al) layers, ferromagnetism in CoSi/Si characterized by strong hysteresis in the magneto-optic Kerr effect, and the anomalous Hall effect at 293 K were observed.     

Temperature and pressure dependence of NMR frequencies in ferromagnetic Heusler alloys containing cobalt and manganese

The ⁵⁹Co and ⁵⁵Mn NMR frequencies ν in Co₂MnZ (Z = Si, Ge, Sn and Ga) were measured as a function of temperature T and pressure P by the cw method. The ν/ν_4.2 value decreased faster for ⁵⁹Co than for ⁵⁵Mn with increasing T/T_C especially in Co₂MnGa, for which ∂ν/∂P was positive at 0°C in contrast to the results in other alloys.     

A note on magnon life-time in itinerant electron ferromagnetic alloys

A model of a binary ferromagnetic alloy A_1?cB_c is discussed in terms of a single band Hubbard type hamiltonian. It is shown by summing up contribution of single-site scattering to all orders, that the inverse life time of long-wavelength magnons due to disorder scattering is proportional to q⁵ and, in the limit c ? 1, to the concentration c.     

Solubility and distribution of substitutional impurities in ferromagnetic alloys

We investigate the solubility of a magnetic substitutional impurity and its distribution over the sites of a face centered crystallographic lattice of an ordered A-B alloy of arbitrary composition, in which ferromagnetism can occur.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 66–72, June, 1986.     

The spin wave stiffness constant in itinerant electron ferromagnetic transition metal dilute alloys

The spin wave stiffness constant is calculated for itenerant electron ferromagnetic transition metal dilute alloys. Calculations are made in the Random Phase Approximation, using the method of effective magnon Hamiltonian. The term in the magnon energy proportional to impurity concentration is calculated by summing up exactly a perturbational series.     

The special features of ferromagnetism in ordered Heusler alloys

The electronic structure and magnetic properties of the Cu₂MnA, Ni₂MnA, Pd₂MnA, Co₂MnA, and Fe₂FeA compounds with cubic lattices, where A is a nontransition element anion (A=Al, In, Ge, As, Sn, Si, or Sb), are studied. An analysis is performed in terms of the generalized Hubbard model with an infinite electronic repulsion energy within the same atom. Equations for determining the spin magnetic susceptibility of the compounds are obtained. These equations are used to determine the conditions of ferromagnetic instability and to construct the phase diagram for the existence of ferromagnetic ordering.     

Mössbauer studies of moment distribution in amorphous ferromagnetic alloys

A spin spatial distribution in terms of an expansion in spherical harmonics containing deviation parameters from the symmetry axis P (0, ?) is used to describe the moment distribution of amorphous ribbon alloys. According to the theoretical analysis and Mössbauer measurement, P (0, ?) values and squareness S_xy (0, ?) and S_z can be obtained. The P (0, ?) distribution of FeNiSiBC and hydrided FeCrSiB amorphous alloys are studied.     

Exchange bias in bulk Ni-Mn-In-based Heusler alloys

The crystal structure and exchange bias of the bulk Heusler alloys Ni₅₀Mn_50−xIn_x with 14.5?x?15.2 have been investigated using X-ray diffraction and magnetization measurements, respectively. Magnetic measurements were performed with SQUID magnetometry after samples were zero-field cooled and field cooled (FC) in positive magnetic fields up to H=50 kOe, from a temperature T=380 K. Three temperatures of the phase transitions, T₁<T_M<T_C, and a shift of the FC (50 kOe) magnetic hysteresis loops up to 120 Oe at 5 K have been detected for all samples. The exchange bias field (H_E) was almost constant for intermediate In concentrations 14.8<x<15.2, and sharply decreased to about 20 Oe on the borders of this concentration interval (x?14.5; 15.2?x). The changes of H_E have been related to changes in the ratio of T₁ to T_M: the overlapping of transitions at T₁ and T_M (for x=14.8, and 15.2) results in a decrease in H_E.     

Calculation of the ordering temperature in Heusler alloys

In the paper we calculate the ordering temperature for ternary solid solutions of variable composition with several sublattices. The results obtained by the Bragg-Williams-Gorskii scheme are compared with those found by the methods of cluster components and other approaches.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 92–95, April, 1981.The authors are indebted to F. A. Sidorenko, N. V. Nikitina, and A. F. Rybalko for their discussions and to K. Yu. Shunyaev for his useful comments.     

Quasi-diamagnetism and exchange anisotropy in Ni-Mn-In-Co Heusler alloys

The quasi-diamagnetism effect that manifests itself in the negative magnetic susceptibility observed in weak magnetic fields during cooling of samples below some critical temperature has been revealed in Ni₄₈Co₂Mn₃₅In₁₅ Heusler alloys. The effect has been attributed to a strong nonequilibrium of the system due to the presence of magnetic and structural disorders and exchange anisotropy.     

Phase transitions in Heusler alloys with exchange inversion

Phase diagrams of the Heusler Ni–Mn–X (X=In, Sn, Sb) alloys with exchange inversion are investigated. It is shown that a few different types of the phase diagrams depending on the signs of phenomenological parameters of the Ginzburg–Landau functional are obtained. In the diagrams there are thermodynamic paths, which can explain the experimentally observed sequences of the phase transitions in Ni–Mn–X alloys.