Tetsuhiko Okamoto

Reentrant ferromagnetism observed in SmMn2Ge2

Magnetic characteristics of SmMn2Ge2 with a layer structure have been studied by magnetization measurements using single crystal. In the sequence of decreasing temperature, ferromagnetism is observed at 196 K ≲ T ≲ 348 K, collinear antiferromagnetism becomes stable for 64 K ≲ T < 196 K and reentrant ferromagnetism appears below 64 K. The appearance of such successive magnetic orderings are attributed to the variation of the shortest Mn-Mn distance due to thermal expansion and the existence of ferromagnetic coupling between the Sm moments in the intralayer which is dominant at low temperatures.

Magnetic Properties of Rare Earth Copper Intermetallic Compounds, RCu2. II. Light Rare Earth

Measurements of magnetization and susceptibility have been made on single crystals of heavy rare earth copper compounds, RCu 2 . All these compounds show metamagnetism with a relative low critical field at 4.2 K. The paramagnetic Curie temperatures along each principal axis are anisotropic. The crystal field parameters V 2 0 and V 2 2 are determined from the values of anisotropic paramagnetic Curie temperatures on the basis of the molecular field theory. These values are in agreement with those evaluated from a point charge model. The neutron diffraction measurements on a TbCu 2 single crystal confirm the collinear magnetic structure.

Magnetic Characteristics of Laves Phase RMn2 Compounds (R=Gd, Tb, Dy, Ho and Er)

Measurements of magnetization, susceptibility, thermal expansion and electrical resistivity have been carried out on the RMn 2 compounds with R=Gd, Tb, Dy, Ho and Er. Magnetization measurements were made on the single crystals for all the compounds. A simple ferrimagnetic structure is observed at 4.2 K for GdMn 2 , HoMn 2 and ErMn 2 , and an antiferromagnetic one in TbMn 2 . While, a canted ferrimagnetic structure appears at 4.2 K in DyMn 2 . The Mn moment deduced from saturation magnetization decreases rapidly from 1.6 µ B for GdMn 2 to 0.2 µ B for HoMn 2 with increasing the atomic number of rare earth in the C15 compounds. While, the Mn moment is almost zero in ErMn 2 with the C14 structure. Anomalous discontinuities in the thermal expansion and resistivity for GdMn 2 and TbMn 2 are observed at the magnetic transition temperature where Mn moments lose a long range ordering. It seems likely that the discontinuity is associated with the onset of the Mn moment.

Temperature Dependence of the Magnetostriction Constants in Iron and Silicon Iron

The magnetostriction constants λ 100 and λ 111 of Fe, 1.08 and 3.83% Si-Fe have been measured by using single crystals at temperatures below Curie point down to liquid air temperature with two newly designed apparatuses. In iron, λ 100 has a minimum around 400°K, while λ 111 monotonously decreases in numeral with increasing temperature. Addition of silicon to iron has a tendency to make the minimum in λ 100 disappear and to decrease λ 111 numerically at any temperature, retaining the similar monotonous variation with temperature. Several existing theories have been applied to account for the experimental results, but no theory appears to be successful in interpreting them.

Magnetic, crystallographic and hydrogen absorption properties of YMn2 and ZrMn2 hydrides☆

Abstract The effect of hydrogen capacity on crystallographic and magnetic properties has been studied on the Laves phase intermetallic of the C15 cubic YMn2 and the C14 hexagonal ZrMn2. It has been found that there exist intermediate metastable β′ phases between the α phase and the fully charged β phase in both compounds. The β′ phase has the same crystal structure as in the hydrogen-free compound and the unit cell volume is smaller than that in the β phase. Magnetization measurements indicate that the β′ phase stabilizes ferromagnetism and, in the β phase, antiferromagnetism or paramagnetism becomes stable. The results obtained are discussed on the assumption that there is a preferential site among the three kinds of tetrahedral hydrogen sites. ZrMn2 exhibited excellent hydrogen absorption properties for use in thermal energy conversion systems operating under high temperatures.

Magnetic phase transitions in PrCo2Si2

Abstract Magnetic phases in PrCo 2 Si 2 have been studied by measurements of magnetization, neutron diffraction and electrical resistivity. For k = (0,0,1) [2π/ c ] is stable. Incommensurate structures k = (0,0,0.926) and (0,0,0.777) appear for 9 K T T

Magnetic and Transport Properties of New Kondo Compounds CeTIn (T=Ni, Pd and Pt)

Measurements of magnetic susceptibility, electrical resistivity and thermoelectric power have been made on the CeTIn system (T=Ni, Pd and Pt) with the hexagonal Fe2P-type structure. The results suggest that CeNiIn is an intermediate valence compound with Kondo-like anomalies in resistivity ?m(T), and CePdIn is a heavy fermion compound with doubie-peak structures in both ?m(T) and S(T) and exhibits an antiferromagnetic order at TN=1.8 K, whereas CePtIn is a heavy fermion peak in ?m(T) and shows no magnetic and superconducting transitions.

Pressure-induced magnetic transition in Fe2P

Abstract The weak field ac susceptibility and the resistivity of Fe 2 P single crystals were measured as functions of temperature from 4.2–300 K and as functions of hydrostatic pressures up to 20 kbar, using a newly designed clamp-type pressure cell. The Curie temperature, and the first-order transition temperature, decreased rapidly with increasing pressure, and ferromagnetism vanished at about 13 kbar at 0 K. A second-order transition temperature, as well as the first-order transition, appeared in the region below 170 K and above 5 kbar (triple point) and a new pressure-induced magnetic phase was found. The phase is proposed to be antiferromagnetic for reasons discussed in the paper.

Magnetic characteristics of TbMn2Si2

Abstract Magnetic structures in TbMn2Si2 were determined by measurements of magnetization and neutron diffraction. The compound has a canted ferrimagnetic structure at T

Magnetic properties of RMn2Ge2 single crystal compounds (R=heavy rare earth)

Abstract Magnetic characteristics in RMn 2 Ge 2 with a layer structure have been studied by measurements of magnetization, electrical resistivity and neutron diffraction. Ferrimagnetic, antiferromagnetic, weak ferromagnetic and paramagnetic behaviours are observed in the sequence of increasing temperature. The transition from ferrimagnetic to antiferromagnetic states is found to be of first order with a hysteresis of 1 deg.