Masao Kiyama

Surface magnetism of α-Fe2O3 by Mössbauer spectroscopy

Abstract α-Fe 2 O 3 particles were prepared from pure 56 Fe and the surface was very thinly coated with 57 Fe. Mossbauer results elucidated that the surface hyperfine field rapidly decreased with increase of temperature but the Morin transition took place at the same transition temperature as the bulk crystal.

NMR Determination of Metal Ion Distribution in Manganese Ferrite Prepared from Aqueous Solution

In order to determine the metal ion distribution in a new type manganese ferrite (MnFe 2 O 4 ), which was prepared by precipitation from aqueous solution, the nuclear magnetic resonance (NMR) of Mn 55 was studied. In this ferrite, two separate resonance signals were observed, which were identified as associated with Mn 2+ ions located at the tetrahedral ( A -) and the octahedral ( B -) sites respectively. By integrating those NMR spectra, it was decided that about 10% of Mn 2+ ions are present at B -sites. Using the ratio of the amount of the Mn 2+ ions located at A -sites to that at B -sites and the value of saturation moment (4.2µ B ), the metal ion distribution in this manganese ferrite was determined to be Mn 0.48 2+ Fe 0.52 2+ (Mn 0.06 2+ Mn 0.46 3+ Fe 1.02 3+ Fe 0.46 2+ )O 4 . From the temperature dependence of the resonance frequency, the Curie temperature was estimated to be 770°K. The high Curie temperature compared with that of ordinary manganese ferrite (573°K) is explainable by the above metal...

Surface Magnetic Properties of γ-Fe2O3 by 57Fe Mössbauer Emission Spectroscopy

Surface magnetic properties of γ-Fe 2 O 3 were studied with the Mossbauer emission spectra of the decayed 57 Fe. The results suggested two surface anomalies: a steep temperature dependence of the surface hyperfine field and a non-collinear spin arrangement in the surface region.

Z2 Vortex-Induced Broadening of the EPR Linewidth in the Two-Dimensional Triangular Lattice Antiferromagnets, HCrO2 and LiCrO2

The title compounds are the family of the AMO 2 -type (R\bar3m) crystal which has a pronounced layer structure and are promising candidates for the two-dimensional Heisenberg triangular lattice antiferromagnet (2DH TAL-AF). The interesting observation is that a singular point of the EPR signal is located around T KM =0.66 J S 2 for the critical temperature of phase transition associated with the pairing-dissociation of the Z 2 vortices, suggesting the present system behaves as 2DH TAL-AF down to very close to T KM . The EPR linewidth exhibits Z 2 vortex-induced broadening above the critical temperature which is inversely proportional to the thermally excited vortex density, n v ∝exp (- E v / k B T ) with the activation energy \(E_{\text{v}}{\cong}4k_{\text{B}}T_{\text{KM}}\).

Mossbauer Effect Study of α-FeOOH and β-FeOOH; Making Use of Oriented Particles

Mossbauer absorption spectra were measured for oriented samples of α- and β-FeOOH particles at antiferromagnetic and paramagnetic states, which were prepared utilizing the anisotropic particle shape. Considering the intensity ratio of six absorption peaks, the direction of the electron spin in antiferromagnetic state was concluded to be parallel to crystal c -axis in each compound. From the intensity ratio of paramagnetic quadrupole doublet, the electric field gradient was discussed. The gradient axis of β-FeOOH was estimated to be in c -plane.

Surface magnetism of α-FeOOH by Mössbauer spectroscopy

Abstract Surface magnetic properties of α-FeOOH were investigated by means of 57Fe Mossbauer absorption spectroscopy. α-FeOOH fine particles were prepared using pure 57Fe isotope and the surfaces of the particles were coated with extremely thin 57Fe(III) layers. Mossbauer results showed that Fe ions in the top surface layer are involved in the magnetic order and the surface hyperfine field rapidly decreased with increasing temperature.

FORMATION AND SOLUBILITY OF BASIC LEAD CHLORIDES AT DIFFERENT PH VALUES

Suspensions prepared by mixing solutions of NaOH and PbCl2 in various mol ratios were subjected to aging at 25, 50 and 80°C. Formation of three kinds of basic lead chlorides takes place, depending mainly on the pH. Their solubilities in the suspension media with various pH values at 25°C were determined.

Surface magnetism of α-FeO(OH) and β-FeO(OH) by Mössbauer spectroscopy

Fine particles of α-FeO(OH) and β-FeO(OH) were prepared using 56 Fe isotope and the surfaces of the particles were coated with extremely thin 57 Fe(III) layers. Mossbauer results show that the Fe(III) ions in the top surface layer are involved in the magnetic order and the surface hyperfine fields rapidly decrease with increasing temperature. The exchange fields at surface sites, estimated from the temperature dependences of the hyperfine fields, are smaller than the bulk values in both cases. The decrease of exchange fields at the surface sites corresponds to the reduced number of neighboring magnetic ions at each site.

Preparation and magnetic properties of BaFe12O19 particles coated with epitaxially grown Fe3O4 layers:6xFe3O4(1 − x)BaFe12O19

Abstract Platelike particles of BaFe 12 O 19 with epitaxially grown Fe 3 O 4 overlayers,6 x Fe 3 O 4 (1 − x )Ba Fe 12 O 19 , were prepared by a wet method. The structure was characterized by X-ray diffraction and TEM and SEM observations. Magnetic properties were studied by VSM and Moossbauer spectroscopic measurements. In order to study the magnetic behavior of very thin Fe 3 O 4 overlayers, Moossbauer measurements were applied to enrich samples, 6 x 57 Fe 56 Fe 2 O 4 (1 − x)Ba 56 Fe 12 O 19 , prepared from alkaline suspensions of Ba 56 Fe 12 O 19 particles and 57 Fe(OH) 2 .

A Mössbauer Study of Magnetic Hyperfine Fields in Fe3+-Antiferromagnetic Oxides

The single-ion hyperfine fields in Fe 3+ ions diluted in KAl 3 (OH) 6 (SO 4 ) 2 , γ-AlOOH and ZnAl 2 O 4 have been measured with the Mossbauer effect in an external magnetic field of 50 kOe at liquid helium temperatures. The values are 570±8 kOe, 565±8 kOe, and 550±10 kOe, respectively, while the previously reported hyperfine fields of the corresponding antiferromagnets at 0 K are 490 kOe, 470 kOe and 515 kOe. The remarkable reductions in KFe 3 (OH) 6 (SO 4 ) 2 and γ-FeOOH indicate large spin deviations due to two dimensional antiferromagnetic interactions.