N. Iwata

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 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

Exchange interaction and magnetocrystalline anisotropy in GdMn2Ge2

Abstract Tetragonal GdMn 2 Ge 2 is a ferrimagnet at low temperatures and changes to an antiferromagnet undergoing a first-order transition at 95 K. The temperature dependence of the magnetization has been analyzed in terms of the molecular-field approximation with interactions between Gd-Gd, Gd-Mn and Mn-Mn atoms. The Gd-Mn interaction is antiferromagnetic, and this permits the appearance of the ferrimagnetic structure at low temperatures. The uniaxial anisotropy (the easy axis of magnetization is the c -axis for both Gd and Mn moments) plays an important role in the first-order ferrimagnetic to antiferromagnetic transition.

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 phase transitions and magnetization process in PrCo2Si2

Abstract The PrCo 2 Si 2 compound has a high-order commensurate structure with a propagation vector Q 3 = (0, 0, 0.777) for T N = 30 K ≥ T > 17 K and a structure with Q 2 = (0, 0, 0.926) for 17 K ≥ T > 9 K , and undergoes a transition between the high-order commensurate structure and a commensurate structure with Q 1 = (0, 0, 1) at 9 K. The magnetic moments are parallel or antiparallel to the c -axis and perpendicular to the ferromagnetic c -planes for all the ordered structures. The magnetization at 4.2 K proceeds by a four-step metamagnetic process. The magnetic transitions and the magnetization process have been studied by introducing a wave-like molecular field H m (i) = Σ q λ(q)〈J q 〉 cos(πqi + φ q ) . Results of the numerical calcul ations made with the Ising spin chain are presented. The wavenumber-dependent molecular field coefficient λ(q) has a maximum at q = Q 3 and is large positive for 1 ≥ q ≥ Q 3 and is negative for 0.4 > q ≥ 0 . The appearance of the magnetic transitions is shown by calculating the free energy. The magnetization at T = 0 K proceeds by three intermediate structures: a structure with Q = 13 14 and m = 1 14 , a structure with Q = 7 9 and m = 2 9 and a structure with Q = 3 4 and m = case |1 4 , where Q is a wavenumber for which the Fourier component of the total angular momentum of the Pr atoms 〈J Q 〉 is a maximum and m is a reduced magnetization. The temperature dependence of the 〈J q 〉 s is also presented in comparison with the neutron diffraction data.

Neutron diffraction studies of PrCo2Si2 single crystal

Magnetic structures of three antiferromagnetic phases in PrCo2Si2 have been determined from neutron diffraction and magnetization measurements on a single crystal. Square-wave structures with propagation vectors k= (0, 0, 1), (0, 0, 2527) and (0, 0, 79) appear in the sequence of T<9K, 9K

Magnetic properties of LaMn2Ge2 single crystal

Abstract Measurements of magnetization have been made on the single crystal LaMn2Ge2 compound. The easy axis of magnetization is the [001] axis. Values of the magnetic moment and anisotropy constant K1 are estimated to be 1.55μB per Mn atom and 2.26×106 erg/cm3 at 0 K. The magnetic moment decreases with increasing temperature following the T3/2 law and K1 decreases as {M(T)/M(0)}1.6. The inverse susceptibility follows the Curie-Weiss and the effective magnetic moment is 3.5μB per Mn atom, and the pc/ps ratio is 1.7.

Metamagnetism in DyCo2Si2

A metamagnetic magnetization process along the 2 Si 2 single crystal. The behavior of the magnetization and the susceptibility is highly anisotropic. The data are well represented by molecular field calculations involving inter-planar coupling constants 1 , 2 , 3 and a constant of coupling within the planes 0 and the crystal-field effect.

Antiferromagnetic to ferromagnetic transition in Y1-xLaxMn2Ge2

Abstract An antiferro-ferromagnetic transition appears in the range 0.25 ≦ x ≦ 0.35 in Y 1- x La x Mn 2 Ge 2 with a layer structure. Experimental results indicate that the magnetic configuration along the c -axis depends on R a Mn-Mn rather than R c Mn-Mn . This is explained by a model that the effective interaction between interlayer Mn moments depends on the stratified density of states.

Exchange interaction and crystalline field in PrMn2Ge2

Abstract Measurements of magnetization have been made on the single crystal of PrMn 2 Ge 2 compound with a layer structure. The compound exhibits ferromagnetism with T c = 329 K. The magnetization and magnetocrystalline anisotropy constant at 0 K are estimated to be 5.9μ B /f.u. and 5.3 x 10 7 erg/cm 3 , respectively, The results have been analyzed in terms of the molecular field theory including the crystalline field.