Soshin Chikazumi

Magnetocrystalline Anisotropy of Low Temperature Phase of Magnetite

The magnetocrystalline anisotropy of low temperature phase of magnetite (Fe 3 O 4 ) was measured for a monoclinic single phase specimen by using computerized fully-automatic torque magnetometer. The anisotropy is expressed by \begin{aligned} E_{\text{a}}=K_{a}\alpha^{2}_{a}+K_{b}\alpha^{2}_{b}+K_{aa}\alpha^{4}_{a}+K_{bb}\alpha^{4}_{b}+K_{ab}\alpha^{2}_{a}\alpha^{2}_{b}-K_{u}\alpha^{2}_{111}, \end{aligned} where α a , α b and α 111 are direction cosines of the magnetization with respect to the monoclinic a -, b - and cubic [111] axes, respectively, the last of which coincides with the longest cube diagonal. The values of the anisotropy constants at 4.2 K are: K a =25.5, K b =3.7, K u =2.1, K a a =1.8, K b b =2.4 and K a b =7.0 in 10 5 erg/cm 3 . It was found that K a , K b and K u exhibit the temperature dependence of an activation type with the activation energy of about 0.02 eV. It was also found that the constants K a a , K b b and K a b are well expressed in terms of cubic K 1 . The mechanism of the an...

Studies on the Magnetic Anisotropy Induced by Cold Rolling of Ferromagnetic Crystal, II. Iron-Aluminum Alloys

Investigation was made on the magnetic anisotropy induced by mechanical rolling of ferromagnetic alloys. Experiments were carried out on the single crystals of Ni 3 Fe through observation of magnetic domain patterns and torque measurements. Easy magnetizing direction was found to be normal to the roll direction for (110) [001] and (001) [100] rolling, while it changes to parallel to roll direction at about 30% reduction for (001) [110] rolling. The maximum value of uniaxial anisotropy was 2∼3×10 5 erg/cc. The results were satisfactorily explained by assuming the appearance of directional order by slip deformation. It was shown theoretically that the anisotropies thus induced are classified into long range order (fine slip) type and short range order (coarse slip) type. Relation to the superlattice formation was also discussed.

On the Origin of Magnetic Anisotropy Induced by Magnetic Annealing

The magnitude of magnetic anisotropy induced by the magnetic annealing was measured as a function of composition for iron-nickel alloys. It is concluded that the magnitude of the anisotropy is proportional neither to the magnetostriction nor to the saturation magnetization. The origin of this anisotropy, therefore, can be explained neither by the theory of “ strain of directional order ” nor by the theory of “ elongated order phase ”. The result can be consistently explained by the dipole. dipole interaction in directionally ordered arrangement of atoms. The result is compared with Neels formulas.

On the Maze Domain of Silicon-Iron Crystal (I)

By using powder pattern technique, the maze-like domain which appears on the mechanically polished surface of Si–Fe crystal was examined. The maze domain was found to be a sort of the closure domain, which transports the magnetic flux of the underlying domains. It was also found that the boundaries between these domains are zigzag-shaped. This is interpreted as a general character of 90° wall. The agreement between theory and experiment is good. The degree of zigzag depends also upon the magnitude of the internal stress. From this relation the internal stresses up to 360 kg/mm 2 was found in the vicinity of the scratch.

Specific Heat and Electrical Conductivity of Low temperature Phase of Magnetite

It was observed for Fe 3 O 4 that the presence of residual stresses lowers the so-called Verwey temperature, T v , considerably, broadens the temperature-width of the anomalous specific heat at T v , produces another additional peak and decreases the discontinuous conductivity change at T v . The entropy change at the phase transition was determined to be 5.4 J /mole·deg but when the effect of short range order is included it becomes 9.6 which is much larger than the value expected for electron hopping under the Andersons restriction. The anisotropic conductivity was measured below T v along the monoclinic axes a , b and c . The magnitude of conductivity was in the order of σ c >σ b >σ a in the range of T v > T >60 K, while it changed to σ b >σ a >σ c below 60 K. The conductivity along [\bar111], or the longest , was also measured by using a squeezed crystal in which a monoclinic single domain is realized. This direction was least conductive among four s in the whole temperature range.

Analysis of Anomalous Thermal Expansion Coefficient of Fe–Ni Invar Alloys

Thermal expansion coefficients of Fe–Ni alloys were analyzed by using the Gruneisen equation. The anomalous thermal expansion coefficient term, α a , was calculated by subtracting the lattice vibration term described by Gruneisen theory from the experimental data. The anomalous volume change obtained by integrating α a was analyzed in terms of the two-states model of iron, the energy separation of which is assumed to be a function of the exchange field and temperature. The temperature dependence of the energy splitting is in good agreement with that of the spontaneous magnetization.

Study of Magnetic Annealing on Ni3Fe Single Crystal

Magnetic anisotropy induced by magnetic annealing was measured for Ni 3 Fe single crystal by means of a high temperature-torque magnetometer. It was found that the magnitude of anisotropy depends upon the crystallographic direction of the field which is applied during annealing. It was largest for , next for and smallest for . It was also found that the minimum of the anisotropy energy lies not in just the same direction as that of annealing field, but in the direction nearer to the neighboring . These facts could be explained qualitatively by Neel-Taniguchi-Yamamotos formula. Quantitative discrepancy between them could be attributed to the nature of face-centred cubic lattice that some of the nearest neighbors of one atom are also in nearest neighbors of one another. Influence of ordinary order was also investigated.

Induced Magnetic Moment in Ferromagnetic Fe Alloys by Tetragonally Elongated Lattice Expansion

Magnetization and Mossbauer spectra were measured for Fe-C, Fe-N and Fe-Ni-C systems. The mass ratio of the tetragonal martensite in the mixed phases was determined by means of Mossbauer spectroscopy, leading to the average magnetic moment of Fe atoms in the body centered tetragonal (bct) structure. The magnetic moment of Fe atoms increases from 2.2 µ B to 2.6 µ B as the axial ratio and the volume of unit cell increase. In other words, the volume expansion and/or the tetragonal elongation seem to cause an increase in the magnetic moment of Fe in bct alloys. It is concluded that the variation of the magnetic moment of Fe in the bct structure can be explained as a superposing effect of both volume expansion and tetragonal expansion. The mechanism of these effects is discussed in terms of energy band splitting of d electrons and magnetovolume effects.

Effects of Atomic Ordering on the Curie Temperature of Fe3Pt

The ferrromagnetic Curie temperatures were measured for ordered and disordered phases of Fe 1- x Pt x (0.25≤ x ≤0.30). The effect of atomic ordering on the Curie temperature was discussed by a pair-interaction model. It was concluded that Fe-Fe pair interaction is negative when only the nearest neighbor pair interactions were taken into account.

Crystal Symmetry of Magnetite in Low Temperature Phase Deduced from Magnetoelectric Measurements

Electric polarization of magnetite, induced by rotating magnetic field in the triclinic b c plane, was measured along the triclinic a axis below 60 K where magnetite is ferrimagnetic as well as ferroelectric. The magnetoelectric polarization was influenced by the way of application of mechanical stress onto the single crystal. Mechanism of this phenomenon was discussed on the basis of the formation of twins including new types. Point group of the crystallographic symmetry of the magnetoelectric single phase was analyzed. It was shown that the present experiment was not inconsistent with the fact that among three crystalline angles, in addition to the a c , at least the b c is not right-angle. Thus magnetite in the temperature range, 4.2 K to 35 K, is of triclinic 1 , irrespective of the magnitude of the angle a b .