Nahonori Miyata

Electric Conduction of Ferrites containing Fe2+-ions

The D.C. electric conductivity was measured between 100°K and 300°K for the ferrite solid solution (MeFe 2 O 4 ) 1- y Fe 3 O 4 ) y , where Me=Mn, Ni, Mn-Ni or Zn. Above 120°K the specific conductivity of each specimen depends on temperature as σ= A ·exp (- e / k T )/ T . The activation energy e is (5∼8)×10 -2 eV. A depends on the concentration, y , of Fe 3 O 4 as A =(6.5±2.5)×10 4 ( y /1- y ) degree/Ωcm. The analysis of these experimental expressions shows that the dependence of the mobility on temperature for each specimen can be fitted by the expression, µ=µ 0 ·exp (- e / k T )/ T and the dependence on the Fe 2+ -ion concentration, y , by µ 0 =(3.0±1.2)×10 1 (1/1- y ) degree (cm 2 /volt sec). µ 0 is independent of the kind and distribution of Me 2+ -ions.

Ferromagnetic Crystalline Anisotropy of MeFe2O4-Fe3O4 Ferrite Solid Solutions

The ferrite crystals of ternary system (Mn x Fe y Ni z )Fe 2 O 4 , where x + y + z =1, were grown by the Bridgman method in the air. According to the X-ray analysis, they have the spinel structure, except in the region near NiFe 2 O 4 , and their lattice constants depend linearly on the concentration: a =(8.518-0.125 y -0.176 z )±0.005 A. The ferromagnetic crystalline anisotropy was measured by the torque method in the temperature range between 90°K and 300°K. In normal specimens K 1 decreases with decreasing temperature. NiFe 2 O 4 –Fe 3 O 4 system shows an anomalous temperature dependence for a wide range of concentration: K 1 increases and changes its sign from negative to positive at low temperature. This will be due to the short range order of Fe 2+ and Fe 3+ at the octahedral site of the spinel lattice. If such an anomaly is subtracted, K 1 of the ternary system becomes maximum at a certain Fe 3 O 4 concentration. This can be attributable to the special contribution of Fe 2+ -ion. The crystal of (Zn...

Exchange Anisotropy of Fe65(Ni1-xMnx)35 Alloys

Ternary alloys of Fe 65 (Ni 1- x Mn x ) 35 have an f.c.c. structure over a whole range of composition and show a transition from ferromagnetic to antiferromagnetic at around the composition of x =0.3. In this transition region it is quite interesting to study their magnetic properties because of the possible coexistence of ferromagnetic and antiferromagnetic regions. This paper mainly deals with the exchange anisotropy of these alloys at low temperatures down to 1.4°K obtained by measurements of rotational hysteresis loss and unidirectional anisotropy. The results show an evidence for the coexistence of ferro- and antiferromagnetic regions at low temperatures. A temperature T K , where the rotational loss disappears due to the small anisotropy constant of antiferromagnetic regions, is considered to indicate a lower limit of the Neel temperature, T N of the regions. Values of T K for x ≤0.4 connect smoothly onto values of T N for x ≥0.4.

Ferromagnetic Crystalline Anisotropy of Fe-Mn-Ferrite System

Ferromagnetic resonance absorption of microwave (9300 Mc/s) in synthetic single crystals of Mn x Fe 3- x O 4 (0.2≦ x ≦1.15) has been investigated to study their magnetic crystalline anisotropy, g -factor and line width. The pronounced valley in the curve, magnetic crystalline anisotropy (- K 1 / M ) v s . composition ( x ), was observed in the temperature region between 90°K and 300°K. - K 1 / M was a minimum in the region 0.6 0.6. It seems difficult to explain these experimental results on the view point of one-ion-model which proved successful in many other ferrites.

Ferromagnetic Crystalline Anisotropy of Pd1-xFex Alloys. I. (\(x{\lesssim}0.3\), FCC Phase)

Magnetic crystalline anisotropy of Pd 1- x Fe x (\(0.1{\lesssim}x{\lesssim}0.3\)) in cubic phase was studied by torque method. An abrupt change was found in the composition dependence of anisotropy constant K 1 at 4.2 K around x =0.17: from +17×10 4 erg/cm 3 for x =0.16 to -6×10 4 erg/cm 3 for x =0.18. Values of K 1 for x =0.26 and 0.33 were negative (-1.2 and -2.6 in 10 4 erg/cm 3 at 4.2 K, respectively) in the quenched state, while, after annealing, they became positive at 4.2 K (+7.0 and +13.0 in 10 4 erg/cm 3 , respectively) and changed their sign with increasing temperature. In the region of \(0.3{\lesssim}x{\lesssim}0.6\), torque curves of quenched specimens depended strongly on magnetic field strength. The results on this region will be presented in the next paper (Part II).

Ferromagnetic Crystalline Anisotropy of Pd1-xFex Alloys. II. (\(0.3{\lesssim}x{\lesssim}0.6\), Quenched)

Ferromagnetic crystalline anisotropy of Pd 1- x Fe x in the range of \(0.3{\lesssim}x{\lesssim}0.6\) was studied by torque method. Because this composition range included tetragonal L1 0 -type superstructure, all specimens were quenched, as rapidly as possible, for realizing cubic structure. In spite of such heat treatment, observed torque curves included a 2-fold symmetry part and their shape was strongly influenced by intensity of magnetic field. These characters suggest coexistence of regions with uniaxial anisotropy in the specimen. They appeared more obviously in the specimen of x =0.42 compared to that of x =0.48. Analysis of the experiment suggests that the usual assumption of neglecting magnetic interaction among regions should be corrected.

Magnetic study on the precipitate from the aqueous solutions of NiCl2 · 6H2O and Na 2SiO3 ·nH2O

Abstract The X-ray powder diffractions, magnetic susceptibility χ and magnetization M were measured for the precipitate from the aqueous solutions of NiCl 2 ·6H 2 O and Na 2 SiO 3 · n H 2 O. From the X-ray and magnetic analysis, the precipitate has the component of monolayer Ni(OH) 2 with the diameter of 20–30A. The temperature dependence of χ and M showed a magnetic transition just above 10 K and field cooling effect.

The effect of heat treatment on ferromagnetic crystalline anisotropy of PdCo alloys

The effect of annealing on the ferromagnetic crystalline anisotropy constant K 1 of Pd 1- x Co x alloys was studied in connection with a short range order structure. Compositions of alloys are x =0.27, 0.30, 0.48 and 0.76. No evidence of occurrence of uniaxial magneic anisotropy was observed for annealed specimen with x =0.48, contrary to the case of quenched PdFe alloys with nearly the same composition which show torque curves changing with magnetic field strength. Negative K 1 was obtained for all specimens in the observed temperature range (below room temperature). The absolute value of K 1 in annealed state was larger than that in quenched one. The difference was obvious for x =0.27 and 0.30 (about 10% at 77 K), while that for x =0.48 and 0.76 (a few per cent) was close to the experimental error.

Magnetic Alignment and Diamagnetic Anisotropy of Cholesteric Liquid Crystalline Poly-γ-Ethyl-L-Glutamate

Abstract The axes of the cholesteric structure of liquid crystalline PELG solution in ethyl acetate tend to be perpendicular to a direction of magnetic field, so that the solution becomes anisotropic in the presence of an applied field. The torque exerted on such anisotropic solutions was measured by appling a magnetic field in a different direction from the original field used for alignment of the cholesteric axes. The anisotropy of diamagnetic susceptibility of the cholesteric structure and that of PELG molecule are estimated from the strength of the torque. The latter is larger than 1.64 × 10-8 emu/g. The average magnetic susceptibilities of PBLG, PEDG and PMLG in the solid state were also measured. These values are in good agreement with those calculated using Pascals additivity rule.

Magneto-thermoelectric Powers of Nickel Single Crystals

The magneto-thermoelectric power (change of thermoelectric power due to magnetization of ferromagnetic substances) and its temperature dependency of nickel single crystals are measured. The ( E m ) 100 and ( E m ) 111 , which specify the characteristic property along the directions [100] and [111] respectively, are calculated under some reasonable approximations. The true magneto-thermoelectric power depends on the orientations of the crystal and is always positive, except that in the neighbourhood of the Curie point which is negative and is due to additive magnetizations proportional to the external magnetic fields, and represents a maximum value near the room temperature and tends to zero at 0°K and also at the Curie point respectively.