Distribution of Hyperfine Fields in Magnetically Anisotropic Amorphous Fe_<100-x>B_x Alloys

The temperature dependence of the Mossbauer spectra of the amorphous Fe_B_x (x=14~21) alloys has been measured. The two distributions of intensity, I_ (H) and I_2(H), which are associated with (±3/2-±1/2) and (±1/2-^-_+1/2), and with (±1/2-±1/2) transitions, respectively, are calculated from the spectra separately. The fact that the shapes of I_2(H) are different from those of I_ (H) at 20K gives evidence that the magnitude and direction of hyperfine fields are not independent of each other, but are correlated. The ratio of the average fields H_2, derived from I_2(H), to H, derived from the hyperfine field distribution P(H), at 20K is dependent on the boron concentration. It is considered that there exists a spatial fluctuation of composition in the samples, and that in the regions where x=17 the magnetization changes its direction easily from parallel to perpendicular to the sample plane, under the stresses caused by decreasing temperature

The Curie Temperature of Magnetically Inhomogeneous Amorphous Fe-Zr-B Alloys

The Curie temperature of amorphous Fe-Zr-B alloys was determined by both the Mossbauer thermal scan and a modified Arrott-plots methods. For amorphous Fe_(Zr_B_x)_8 alloys, the two methods make a difference between the values of T_c. On the other hand, for amorphous Fe_(Zr_B_x)_ alloys, the results of the two methods agree with each other within limits of the experimental error. It is found that the magnetic inhomogeneity often causes the difficulty in the determination of T_c and the measurement of T_c necessitating external fields is accompanied by a serious problem in the case of the magnetically inhomogeneous materials. Since no external field is necessary, the Mossbauer thermal scan method is very useful for determining T_c of amorphous alloys containing Fe atoms

Asymmetry in the Mossbauer Spectra of Amorphous Fe_<100-x>B_x (14≤x≤21) Alloys

The Mossbauer spectra of amorphous Fe_B_x (14≤x≤21) alloys which are slightly asymmetric are analyzed in terms of the distributions of hyperfine fields and isomer shifts. On the assumption that the correlation between hyperfine fields H and isomer shifts I. S. is described by I. S.=c_0+c_1・H, where c_0 and c_1 are constants, the value of c_1 is dependent upon the concentration as same as c_0. While the change of c_0 is connected smoothly to the isomer shifts of crystalline α-Fe, Fe_2B and FeB, the value of c_1 which explains the asymmetry is sensitive to the amorphous structure

Neutron Irradiation Effects on Magnetic Properties of Some Heusler Alloys(Metallurgy)

The neutron irradiation effects were studied with measurements of temperature dependence of magnetization in ordered and disordered Heusler alloys. The irradiation was carried out in JMTR with a total flux of fast neutrons of 10^ nvt. Fully ordered Cu_2MnIn, partially ordered Cu_2MnAl and completely disordered Cu_2MnSn were prepared with various temperature treatments. The magnetization-temperature curves of each specimen were measured before and after irradiation. In the irradiated Cu_2MnIn, the disordering by the irradiation gave rise to a decrease of magnetization, and the temperature dependence of magnetization showed that the disordered region contained various regions with different degrees of disorder. For the distribution of the disordered region, the calculation based on the theory of temperature spike by Seitz and Koekler gave a feasible result that a disordered region comprised a central core with a radius of 5.4 A which was completely disordered and a periphery of 3.3 A thickness which was partially disordered. From the magnetization-temperature curves of Cu_2MnAl, it was considered that the disordered regions induced by the irradiation had different properties from those induced by the heat treatment. The former were the localized and comprised regions corresponding to various degrees of disorder, while the latter spread spatially in a wide range with a certain degree of disorder. The ordering by enhanced diffusion occurred simultaneously to an extent comparable to the disordering, and so it played an important role in the magnetization in the partially disordered Cu_2MnAl. In the disordered Cu_2MnSn, however, the ordering effect was very small. It is supposed to be difficult for the A2 structure to transform into the L2_1 structure by the enhanced diffusion

Magnetic Properties of Ternary DyMn_2X_2 Compounds (X=Si and Ge)(Magnetism)

Magnetic properties of DyMn_2Si_2, DyMn_2Ge_2 and their mixed compounds DyMn_2(Si_Ge_x)_2, which display a variety of interesting magnetic behaviors originating in competing magnetic interactions and anisotropy, have been investigated systematically by magnetization mesurements ^Dy Mossbauer spectroscopy and neutron diffraction experiments. This report presents a review of the results mainly obtained by the magnetization measurements

Magnetic Phase Diagrams with Possible Field-induced Antiferroquadrupolar Order in TbB2_2C2_2

Magnetic phase diagrams of a tetragonal antiferromagnet TbB$_2$C$_2$ were clarified by temperature and field dependence of magnetization. It is noticeable that the N{\'e}el temperature in TbB$_2$C$_2$ is anomalously enhanced with magnetic fields, in particular the enhancement reaches 13.5 K for the ${}$ direction at 10 T. The magnetization processes as well as the phase diagrams are well interpreted assuming that there appear field-induced antiferroquadrupolar ordered phases in TbB$_2$C$_2$. The phase diagrams of the AFQ compounds in RB$_2$C$_2$ are systematically understood in terms of the competition with AFQ and AFM interactions.Comment: 4 pages, 4 figures, RevTeX

Mossbauer Spectrometer for Measurements in High Magnetic Fields(Part II. Several Instruments and Techniques Developed in HFLSM)

A Mossbauer spectrometer has been designed and constructed for measurements in high magnetic fields beyond 20 T which are generated by a hybrid magnet in the High Field laboratory for Superconducting Materials at Tohoku University. Simple ways were adopted in order to avoid some obstacles for the spectroscopy. The most serious problem was electromagnetic inductions occurring at metallic components in a source drive system. It was found that the replacement of an aluminum drive-rod to a Bakelite one improved remarkably the Mossbauer spectrum. Test measurements of a-Fe at room temperature were satisfactorily performed under the magnetic fields up to 10 T. The results agreed well with the theoretical expectation