Takasu Hashimoto

Magnetic Properties of Potassium Iron Group Fluorides KMF3

Evidence of antiferromagnetism in perovskite-type potassium iron group fluoride KMF 3 was found through the susceptibility measurements made between 80°K and 700°K. The obtained results are as follows:

Antiferromagnetism of γ-FeMn Alloys. III. Specific Heat and Thermoelectric Power Studies

The specific heat and the thermoelectric power of γ-FeMn alloys were measured for three different compositions. The peak of the specific heat at the Neel temperature is broad for Fe 70 Mn 30 but it becomes sharp when the concentration of Fe decreases. This tendency is interpreted in terms of the temperature variation of the sublattice magnetization of the alloys. The magnetic entropies obtained are 1.4, 0.83 and 0.57 cal/mol. deg. for Fe 70 Mn 30 , Fe 60 Mn 40 and Fe 50 Mn 50 respectively. These values are nearly a half of those estimated for the localized spin system. The thermoelectric power is also strongly composition dependent. The temperature dependence of the thermoelectric power suggests that two types of carriers exists in the alloys. Only a small anomaly was observed at the Neel temperature. The results suggest that the antiferromagnetism of γ-FeMn alloys is distinctly different from that of Cr.

The Nonlinear Magnetic Susceptibility of YIG in the High Frequency Magnetic Field near the Curie Temperature

In order to obtain the information about nonlinear terms of the high frequency magnetic susceptibility at 2MHz near the Curie temperature the 2nd and 3rd order nonlinear terms against the high frequency magnetic field are derived from the observations of the 2nd and 3rd harmonics. Both terms decrease abruptly as the temperature deviates from the Curie temperature. It is a very remarkable result that the 2nd harmonic signal is observed above the Curie temperature in contradiction to the simple theoretical consideration. As for the 3rd harmonic its temperature dependence is explained qualitatively by the molecular field theory.

Magnetic Properties of Cr3Te4 in Ferromagnetic Region

Single crystals of Cr 3 Te 4 with the pseudo-NiAs type structure have been made by chemical transport method in order to investigate the anomaly below 80 K. The saturation moment at 4.2 K is equal to 1.79±0.03 µ B per Cr 1- x Te (x=0.25), and the Curie temperature is 316 K. The magnetization only in the direction to the a -axis shows the anomaly that the saturation field increases abruptly below 80 K, which corresponds to the Neel point proposed by Andresen. But on the contrary to his result, the easy axis of the moment is parallel to the c -axis in the whole ferromagnetic region and antiferromagnetic order appears only in the c -plane. By a spin echo method, two nuclear magnetic resonance absorption lines of Cr 53 -nuclei are observed at 45.3 and 57.5 MHz at 4.2 K. The resonance frequencies increase remarkably below 80 K. This fact may support subsidiarily the existence of the antiferromagnetic order below 80 K.

ESR Investigation of TGS Doped with Cr3+ Ions

We observed the ESR signal of Cr 3+ ions in triglycine-sulphate. It is found that a pair of lines gradually approach to each other with increasing temperature in the ferroelectric phase and converge at the Curie temperature. The results are interpreted by using the concept of motional narrowing on the basis of the model of order-disorder type. The linewidth for the applied magnetic field nearly parallel to the principal axis z shows an anomalous increase near the Curie temperature. The critical exponent of the linewidth in the ferroelectric region is determined to be 0.5 in the vicinity of the Curie temperature and to be 2.0 far from the Curie temperature.

Magnetic Properties of the Solid Solutions between KMnF3, KCoF3 and KNiF3

In order to obtain informations on superexchange interaction, the magnetic susceptibility of KNiF 3 and the solid solutions between KMnF 5 , KCoF 3 and KNiF 3 has been measured in the temperature range between 80°K and 850°K. The values of exchange integral | J / k | between the two adjacent magnetic ions are derived by use of the molecular field approximation and by use of the Danielian-Stevens(D-S) procedure as follows:

Spin Relaxation on Yttrium Iron Garnet near Curie Temperature Studied by High Frequency Magnetic Susceptibility

The high frequency magnetic susceptibilities in yttrium iron garnet are observed in the temperature range from 546 K and 553 K in the high frequency range from 100 kHz to 100 MHz and the low frequency range lower than 100 Hz. The anomalous sharp peak appears in the temperature dependence curves of the imaginary part of the magnetic susceptibility in MHz range and is broadened with increasing frequency. From frequency dependence of the magnetic susceptibilities it is made clear that the relaxation of spin system occurs in the above two frequency ranges and relaxation process near the Curie temperature is not monodispersive but polydispersive. The temperature dependence of the relaxation time in spin system is obtained near the Curie temperature and is corresponding with the critical slowing down phenomena.

Relaxation Time of Spin System in K2CuF4 near Tc Determined by Magnetic Susceptibility Measurement in High Frequency Magnetic Field

The magnetic susceptibilities of K 2 CuF 4 in a high frequency magnetic field were measured in the frequency range from 3 MHz to 64 MHz and in the temperature range from 5.5 K to 7.5 K using a Sche...

A New Type of Polydispersive Spin Relaxation in Mn-Zn Ferrite near Tc

The spin relaxation process in (Fe 0.06 Mn 0.60 Zn 0.34 )Fe 2 O 4 has been investigated near T c in the paramagnetic region by magnetic susceptibility measurement in a high frequency (MHz) magnetic field. This process is polydispersive and the frequency dependence of magnetic susceptibility is explained by a similar formula to the one introduced by Cole and Cole, and Matsubara and Yoshimitsu. Moreover, it is observed that the relaxation process becomes more polydispersive with the approach of T c . These experimental results are explained qualitatively by using the Glauber model and the molecular field approximation.