Yoshiya Adachi

Magnetic Structure of Rhombohedral Cr2Se3

Rhombohedral Cr 2 Se 3 is an antiferromagnetic compound with antiferromagnetic AF(L) phase below 38 K (= T t ) and the antiferromagnetic AF(H) one between 38 K and 45 K (= T N ). Neutron diffraction studies for rhombohedral Cr 2 Se 3 are carried out at temperatures from 6 K to 77 K. The results show that the magnetic structures of AF(L) and AF(H) phase are a non-collinear and collinear antiferromagnetic structures, respectively, with the monoclinic magnetic unit cell. It was found that Cr moments at the a-sites are frustrated in the AF(H) phase.

Thermal expansion in chromium chalcogenides Cr2X3 (X=Se, Te)

The lattice parameters a ( T ) and c ( T ) as a function of temperature ( T ) for rhombohedral-Cr 2 Se 3 and trigonal-Cr 2 Te 3 have been measured in the temperature range between 15 K and 300 K. As T increases, a ( T ) for Cr 2 Se 3 increases up to a magnetic order-order transition temperature T t above which it suddenly shrinks with the change Δ a / a =-1.1×10 -3 , while c ( T ) smoothly increases through T t . In Cr 2 Te 3 , a ( T ) decreases up to about 250 K and then increases while c ( T ) increases in the temperature range measured. The obtained results are qualitatively discussed on the relation beteen the moment stability and volumetric expansion.

A Gifford-McMahon Cycle Cryocooler below 2K

According to theory, a Gifford-McMahon (GM) cycle cryocooler with 4He cannot cool below 2 K because of the 4He superfluid transition near this temperature. However replacing 4He by 3He removes this temperature limitation. The cooling performance of a GM cryocooler with a HoCu 2 magnetic regenerator material is investigated using 3He. The minimum temperature of 2.3 K with 4He goes down to 1.65 K when the 4He working fluid is replaced by 3He. The maximum cooling capacity at 2 K is 53.9 mW with a compressor power of about 2.5 kW, and the cooling capacity at 4.2 K is enhanced by more than 20%.

Magnetic properties of the Cr2S3−xSex and Cr2Te3−ySey systems

Abstract Magnetic and crystallographic properties of the Cr2S3−xSex and Cr2Te3−ySey systems were investigated. An obvious transition point from ferrimagnetism or ferromagnetism to antiferromagnetism cannot be observed in both systems. But at low temperature, mictomagnetism was found in the range of x = 0.9−2.7 of the Cr2S3−xSex system and y = 0.7−2.1 of the Cr2Te3−ySey system. An interesting result was found in a relation between the paramagnetic Curie temperature θp and the lattice parameter ratio c / a.

Pressure effect on the Néel temperature of Cr2Te3−xSex

Abstract The Neel temperature ( T N ) of ferrimagnetic pseudobinary compounds Cr 2 Te 3− x Se x is examined as a function of Se concentration ( x ) and pressure ( p ). It is found that T N decreases with increase of x or p , respectively. The results are discussed in relation with the lattice parameters a and c dependence of magnetic properties of Cr 2 Te 3 .

Neutron diffraction study of Nd3Co

The ferromagnetic compound Nd3Co has Curie temperature TC=25 K and the spin reoriented temperatures TR1=8.5 K and TR2=14 K. Neutron powder-diffraction measurements of Nd3Co were carried out at 50 K above TC and at 2.1 K below TR1. The magnetic structure at 2.1 K was determined, whose unit cell has the volume of 2a×b×2c. The values of magnetic moment on Nd atoms in 4c and 8d sites were 2.47 and 3.08 μB, respectively. This magnetic model is consistent with the results of magnetization curves of a single crystalline Nd3Co.

Magnetic phase diagram of Cr2S3−xSex system

It is found that the Neel temperature for x > 1.4 in the Cr 2 S 3− x Se x system increases with x , and a field cooling effect at low temperature occurs between x = 1.4 and 2.1.

Crystalline electric field effect in single crystalline HoNi

The heat capacity of HoNi was measured in the temperature range from 1.7 to 80 K. The Schotky-type anomaly was explained by the crystalline electric field effect on the basis of the point charge model.

HIGH FIELD MAGNETIC PROPERTIES IN SINGLE CRYSTAL ND3CO

Magnetization as a function of field was measured in pulsed fields of up to 40 T at various temperatures along the principal axes of single crystal Nd3Co. Along the a axis we observed metamagnetic transitions at fields of 1.9 and 4.5 T at 4.2 K. We also observed a sharp increase in the magnetic moment in applied fields between 9.5 and 14 T. Along the b axis a metamagnetic transition was observed at a field of 1.5 T at 4.2 K. Along the c axis we observed ferromagnetic behavior. The H–T (magnetic field and temperature) phase diagram was obtained using a superconducting quantum interference device magnetometer.

Magnetic Properties of Single-Crystalline Pr3Co

Magnetization curve, magnetic susceptibility and electrical resistivity were measured for Pr 3 Co single crystals. The magnetization curves at 1.5 K were measured in magnetic fields up to 7 T. Metamagnetic transitions were observed at 0.85 T along the a -axis and 6.4 T along the b -axis, respectively. From the magnetic susceptibility, the effective magnetic moment is deduced to be 3.59 µ B /Pr ion, which is in good agreement with the Pr 3+ free ion value.