Magnetostrictive Model Research Articles

Magnetic and dielectric properties of the spinel ferrite system Ni0.65Zn0.35Fe2−xMnxO4

The recent development of a high-magnetization nickel–zinc ferrite with stress-insensitive square hysteresis loop achieved through substitution of Mn3+ ions has prompted a study of the family Fe3+0.65Zn2+0.35 [Ni2+0.65Fe3+1.35−xMn3+x]O4. The magnetic and dielectric properties of compositions with x ranging from 0 to 0.4 were measured to determine the effects of the manganese substitutions over this concentration range. As anticipated, the saturation magnetizations decreased gradually with increasing x because of reduced magnetic moments in the B sublattice. Of greater importance, however, was the observation that maximum hysteresis loop squareness and minimum stress sensitivity occurred with x∼0.2. A single-ion magnetostriction model is used to interpret this result. Since the electrical resistivity remained above 106 Ω cm and the dielectric loss tangent stayed below 10−3 for the entire series, Fe2+ ion formation is probably negligible.

Linear magnetostriction in polycrystalline Ni-Fe-Cr and Ni-Fe-V alloys

The linear saturation magnetostriction λ s has been measured in some polycrystalline samples of Ni-Fe-Cr and Ni-Fe-V alloys on which the extraordinary Hall conductivity YHs was measured earlier. The λ s ≈ 0 lines on the ternary alloy composition diagrams are found to lie below those predicted by the split-band model and much above the YHs ≈ t 0 lines. However, the present λ s data on polycrystalline samples are quite close to the λ s ≈t 0 lines derived from the already existing single crystal data. The λ s ( T) curves are qualitatively explained in terms of the existing localized model for magnetostriction.

Anisotropy Fields on Implanted (100) Magnetic Garnet LPE Films

LPE-grown (100) magnetic garnet films were implanted with He+ ions under different conditions and annealed at 300°C, and the effect on the anisotropy field was studied. The field H k1 for implanted layers was less than half that of unimplanted films, and decreased with increasing temperature; the change in effective anisotropy field ?(H k -4?M s ) related to the magnetostriction constant ? 100 is large at high temperatures. The temperature characteristic of change in effective anisotropy field ?(H k -4?M s ) exhibits an anomalous shift near T c , which cannot be explained via a simple magnetostriction model.

鉄基低磁気ひずみ非晶質合金の透磁率と熱安定性

Magnetic permeability and its thermal stability have been investigated in low magnetostrictive amorphous Fe-based alloys. Crystallization temperature, Curie temperature, saturation magnetization, and effective permeability up to 1 MHz have been measured. A value for the effective permeability of 2×104 is obtained at 1 kHz for Fe-based amorphous alloys with low magnetostriction of the 10-6 order, which is comparable to the value of zero magnetostrictive Co-based amorphous alloys.Disaccommodation and thermal variation of magnetic permeability have been also measured. Small disaccommodation, good thermal stability, are achieved in low magnetostrictive Fe-based amorphous alloys. Disaccommodation, however, is not directly proportional to λs2 in the 10-6 range of magnetostriction, suggesting that the magnetostrictive model of Allia is not valid in low magnetostrictive Fe-based amorphous alloys. Even for Fe-based amorphous alloys, disaccommodation should be considered in terms of induced magnetic anisotropy, in addition to the magnetostriction.

Structural Lifshitz point in the quasi d = 1 magnetostrictive XY model

We obtain, within a framework in which the crystalline degrees of freedom (assumed essentially three-dimensional) are adiabatically treated and the magnetic degrees of freedom are exactly (approximately) treated in the disordered (ordered) phase (s), the peculiar phase diagram of the d = 1 first-neighbour spin- 1 2 magnetostrictive XY model in the presence of a magnetic field along the Z-axis. The structural instability wavevector continuously varies along the (2nd order) critical line. This variation presents two non-trivial points: one of them corresponds, in the phase diagram, to a Lifshitz point, where the uniform and dimerized phases converge with a (complex) modulated one; the other one presents characteristics which, to the best of our knowledge, have never been observed.

Spin anisotropy effects on the dimerization of the magnetostrictive quasi-one-dimensional XY model

The one-dimensional first-neighbour spin - 1 2 magnetostrictive XY model (with crystalline degrees of freedom assumed three- dimensional) with different X and Y spin coupling constants presents a quite rich spin-Peierls dimerization phase diagram. In the (low anisotropy) - (low temperature) region we recover previous results (in particular the possibility for a first-order phase transition in the absence of external magnetic field); in the other three regions of the temperature-anisotropy space interesting branches of the phase diagram (including the tricritical line) are exhibited (for the first time as far as we know).

Dimerization in the magnetostrictive one-dimensional XY model

We discuss the one-dimensional first-neighbor 1 2 -spin magnetostrictive XY model (where the crystalline degrees of freedom are assumed to be three- dimensional), and exhibit that, for all temperatures below T c , no other contributions to the structural order appear than the pure dimerization one. The influences of temperature and elastic constant on the order parameter and sound velocity are analyzed as well.

Columnar model of magnetostriction in amorphous films

Columnar model of magnetostriction in amorphous films

Influence of the surface anisotropy on the r.f. collapse effect

The influence of magnetic surface anisotropy on the fast relaxation of the hyperfine field forced by an r.f. field in invar (r.f. collapse effect) has been studied using the Mössbauer technique. The Mössbauer measurements were performed as a function of sample thickness (2.5–12 μm) and intensity (1–9 Oe) of the 50 MHz r.f. field applied. Due to the very high sensitivity of the r.f. collapse effect to the anisotropy field it was possible to detect the influence of “spin pinning” on the r.f. collapse effect. It is shown that a decrease of the sample thickness causes a decrease of the r.f. collapse effect at a given r.f. field frequency and intensity which is connected with the increase of the anisotropy field due to surface anisotropy. The dependence of the r.f. sidebands effect, which accompanies the r.f. collapse effect, on the sample thickness is discussed. The r.f. sidebands effect increases with decreasing sample thickness, which is in good agreement with the magnetostriction model of sidebands formation.

An exactly soluble model of quadratic magnetostriction

Spin-phonon coupling, quadratic in the lattice displacements, is studied assuming that the spin interactions are of infinite range. The magnetic phase transition changes from second to first order for a sufficiently strong coupling. The ferromagnetic spinodal temperature becomes infinite and the paramagnetic spinodal temperature becomes zero for couplings of appropriate signs and strength. Renormalization of the phonon frequencies, within both the Einstein and the Debye schem schemes, is found.

Temperature dependence of the effective linewidth in porous and fine grain polycrystalline yttrium iron garnet

Data on the temperature dependence of the off-resonance effective linewidth \DeltaH_{eff} have been obtained at 9.94 GHz for porous and fine grained samples of polycrystalline YIG. The high field \DeltaH_{eff} increases with decreasing temperature from 300K to 250K. From 250K to 100K, \DeltaH_{eff} is constant. \DeltaH_{eff} is linearly proportional to porosity, with about 0.4 Oe/%, which is superimposed on a porosity independent contribution which increases from a few tenths Oe at 300K to about 2.2 Oe below 250K. For samples with an average grain size a o of 3μ to 30\mu, \DeltaH_{eff} is proportional to a_{o}^{-1/2} at 300K and to a_{o}^{-1} below 250K. These results are discussed in terms of a magnetostriction model and a spin-wave transit time model.

Mössbauer study of FM sidebands produced by the RF magnetic field applied to an iron foil

AbstractThe formation of rf sidebands in the Mössbauer spectra of metallic iron as a result of the application of an external rf magnetic field is studied. The dependence of the sideband intensities on the rf field intensity and the thickness of the sample is discussed. Experiments show that the formation of sidebands is connected with atomic vibrations induced within the foil by the rf field applied. Basing on the experimental spectra obtained, modulation indices are calculated in accordance with the FM theory. The results obtained are interpreted in terms of the modified magnetostriction model. The dependence of sideband formation on the coating of the foil with a damping medium is studied. It is found that covering of the sample surface with a silicon grease, adhesive tape, or metallic zinc causes a considerable damping of the sidebands and in some cases causes their complete quenching. This effect has been attributed to the dissipation of energy generated within the sample by the rf field. If the acoustic resistivity of the medium covering the sample is higher than that of air the energy transferred from the foil to the environment increases and the sidebands are damped.

Linear Magnetic Birefringence in Transition Metal Oxides: CoO

AbstractThe optical linear magnetic birefringence (LMB) of cobalt oxide single crystals was determined as a function of temperature near the antiferromagnetic Néel point. The measurements were taken from single‐domain crystals with the tetragonal c‐axis oriented parallel or perpendicular to the direction of the light beam. Below TN the change of LMB with temperature in perpendicular arrangement is found to be proportional to the c‐axis contraction and to the square of the long‐range order parameter. Magnetic short‐range order effects have been observed even far above TN. The results are discussed by means of a magnetostriction model.

Solvable Compressible Ising Model

The results for the solvable Baker-Essam model of a compressible Ising lattice are rederived by utilizing the equivalence of the system to a set of linear chains each described by the Mattis-Schultz one-dimensional magnetostriction model.

A model of magnetostriction in an Ising system and its application to PrCl3and NdCl3

A magnetostriction model for a second order phase transition in an insulating antiferromagnet is proposed and solved, treating the spin system in the two chain approximation with the distortion in the mean field approximation. The solution obtained agrees well with the experimental PrCl3 data but badly with the corresponding NdCl3 data.

Magnetic Domain Nucleation and Propagation in Fine Wires

The effect of material composition and structure on the magnetic domain nucleation field (Hn) and the domain wall propagation field (Hp) in fine cold-drawn Permalloy wires is reported. Binary Ni/Fe wires (Fe>20%) were reentrant (Hn>Hp) when cold drawn to less than 250 μm diam. Alloying additions inhibited stress recovery during drawing and annealing and thereby increased and stabilized Hn. Variations in Hn along the wire length correlated with defects in the wire surface. Sputter coating the wire improved the surface condition and reduced variations in Hn. A magnetostrictive model of re-entrancy is proposed and discussed.

Magnetostriction of polycrystalline silicon iron sheet

A model of magnetostriction of ferromagnetic polycrystalline sheet has been devised based on the orientation distribution of the crystals and the domain theory of magnetization. Comparison with experimental data for silicon iron shows that the model gives a good numerical agreement at a flux density of 15 000 gauss and a good qualitative description of the dependence of magnetostriction on flux density. It shows also that magnetostriction is sensitive to the preferred orientation of the material and that variations in measured magnetostriction are largely attributable to differences in the orientation distribution.