V. Šíma

The effect of local disorder on the magnetic, electric and thermal properties of RE(Fe1-xAlx)2 (RE=Gd, Dy)

Measurements of magnetic properties, X-ray and neutron diffraction, differential thermal analysis (DTA), thermal expansion and resistivity were made on Gd(Fe1-xAlx)2 and Dy(Fe1-xAlx)2. Both systems exhibit a line broadening observed by X-ray diffraction on the Al-rich side, indicating a small variation of the lattice constants. This effect leads to a smoothing of the magnetic phase transition at the Curie temperature Tc, which becomes observable in all the measurements mentioned above. The neutron experiments give evidence of a disordered component of the Dy moment due to Fe substitution. By subtracting the thermal expansion of non-magnetic YAl2 from that of the mixed crystal series, a reduction of the spontaneous magnetostriction from its value in the corresponding boundary phase is also obtained. In the case of anisotropic Dy the magnetisation behaviour can be explained by the pinning of narrow domain walls on inhomogeneities caused by chemical substitution. All physical properties indicate a magnetically quasi-amorphous state.

Neutron diffraction study of the magnetic structure of HoCu2

Abstract Neutron diffraction measurements show that in the temperature range from 7.4 to TN=10.4 K the magnetic structure of HoCu2 is a commensurably modulated a-axis collinear structure with a wave vector q1=1/3a∗. Below 7.4 K an additional structure component develops and the low temperature magnetic structure of HoCu2 is found to be an incommensurably modulated non-collinear structure characterized by wave vectors q1=/13;a∗, q2=qcc∗ and 2q2, where a∗ and c∗ are reciprocal lattice vectors of the orthorhombic structure and qc=0.300±0.005. The corresponding moment components μ-q1, μq2 and μ2q2 lie along the a, b and b directions of the orthorhombic crystal lattice, respectively.

Magnetic arrangement in the Dy(Fe1−xAlx)2 pseudobinary laves phases

Abstract The magnetic structure and magnetic moments of Dy and Fe have been studied at 4.2 K by means of neutron diffraction measurements on powdered samples of Dy(Fe 1− x Al x ) 2 for x=1.0, 0.9, 0.3 (the C 15 structure) and for x=0.5 (the C 14 structure). A strong reduction of the Dy-moment for x≤0.9 is explained by the crystallographic disorder in the Fe-Al sublattice as well as lattice defects.

Temperature dependence of the magnetic structure of TbCu2

Abstract The orthorhombic compound TbCu 2 was studied by neutron powder diffraction. The temperature development of the magnetic structure is interpreted by means of Fourier analysis of the diffraction data below T N = 55 K .

Neutron diffraction study of the R(Cu1-xNix)2(R = Tb, Ho) system

Abstract Neutron diffraction study on powder samples of Tb(Cu1-xNix)2 with x = 0.00, 0.05, 0.10 and Ho(Cu1-xNix)2 with x = 0.00, 0.10 was performed at T = 4.2, 2.5K and above ordering temperature. In both cases (R = Tb, Ho) for x = 0.10 the decreasing concentration of conduction electrons gives rise to predominate ferromagnetic component.

On crystal-field spectroscopy based on specific heat and thermal expansion measurements: application to the TmCu2 intermetallic compound

An experimental study based on specific heat, thermal expansion, magnetisation and neutron diffraction measurements on polycrystal and single crystal of the orthorhombic TmCu2 compound is presented. The results are satisfactorily interpreted within a model involving the crystal and molecular field acting on the Tm3+ ions. The energy spectrum of the ground-state multiple 3H6 of Tm3+ with the isolated split lowest quasi-doublet ( Delta 1=5+or-1 K, Delta 2=68+or-3 K) is proposed. The appropriate sets of crystal-field parameters Vlm are obtained and discussed.

On the temperature dependence of the sublattice magnetizations in TbCu2

Abstract Calculations based on molecular and crystal field models were used for the interpretation of the temperature dependence of the sublattice magnetizations found by neutron diffraction in the antiferromagnetic compound TbCu 2 . The observed dependence is explained as a result of comparable amounts of exchange and crystal field energy in this compound.

Magnetic phase transitions in TmCu2

Magnetisation, susceptibility, resistivity and specific-heat measurements on TmCu2 reveal magnetic transitions at 3.3K, 3.9K, 4.3K and 6.3K, which reflect a change of magnetic structure and Neel temperature. These transitions are strongly field dependent. The behaviour of TmCu2 is very similar to that of ErCu2 and therefore a complicated magnetic structure should be expected.

Magnetic structures of R(Cu, Ni)2 compounds (R = heavy rare earth) studied by neutron diffraction

Magnetics structures of powdered orthorhombic R(Cu, Ni)2 compounds (R = heavy rare earth) determined by neutron diffraction are described. The influence of magnetocrystalline anisotropy and exchange interactions on the type of magnetic ordering is discussed.

Magnetic phase transitions in Tm(Cu1−xNix)2

Abstract The crystal field ground state quasidoublet was established for Tm(Cu 1− x Ni x ) 2 ( x ⩽0.3) using specific heat experiments. The magnetization isotherms were described through an effective spin S = 1 2 Hamiltonian. The change from AF to F ordering was observed for this induced moment system with increasing x .