Hanania Ettedgui

MAGNETIC PROPERTIES OF TBCO3B2 STUDIED BY NEUTRON DIFFRACTION, MAGNETIZATION, AND AC-SUSCEPTIBILITY MEASUREMENTS

Neutron-diffraction measurements on TbCo3B2, with the isotope 11B, show ferromagnetic structure below 35(2) K. Ordered magnetic moments of Tb and Co were found to be in the basal planes directed parallel to each other. The Tb ordered moment is significantly smaller than its free-ion value. The Co ordered moment is nearly zero. Ac-susceptibility and SQUID magnetometer measurements agree with the neutron results.

Magnetic phase diagram of the U(Ni1−xCux)2Ge2 system

Abstract Polycrystalline U(Ni 1- x Cu x ) 2 Ge 2 solid solutions, investigated by neutron diffraction and AC susceptibility, exhibit the ThCr 2 Si 2 -type crystal structure and magnetic ordering of the uranium sublattice, with moments along the tetragonal axis: antiferromagnetic type-I (AF-I) [ k =(0,0,1)] for x =0,0.25, and 0.50; ferromagnetic below T c , becoming at T 0 ( T c ); AF-I for x =0.75 and ferrimagnetic [ k =(0, 0, 2/3)] for x =0.90; and ferromagnetic for x =1. The tentative magnetic phase diagram ( T versus x ) of the U(Ni 1- x Cu x ) 2 Ge 2 system is proposed.

Magnetic structure of the solid solution UNiCuSi2: Neutron diffraction versus ac‐susceptibility measurements

Polycrystalline samples of the solid solution UNiCuSi2 have ThCr2Si2‐type crystallographic structure. ac susceptibility indicates an antiferromagnetic (AF) transition at TN=150±5 K, followed by four transitions with ferri/ferromagnetic (F) character at 110±5, 90±5, 70±5, and 45±5 K. Neutron diffraction shows that apart from the AF transition at TN=150±1 K, in accordance with the ac susceptibility, none of the other F transitions is observed. The magnetic structure, down to 1.7 K, is AF‐I, with uranium moments (2.25±0.10μB at 1.7 K) along the tetragonal axis in ferromagnetic planes, stacked antiferromagnetically (+−+−) along the tetragonal axis, with a wave vector k=(0,0,1). A possible explanation for the difference between the ac susceptibility and neutron‐diffraction results is discussed.

Magnetic ordering in the solid solutions UCoNiSi2 and UNiCuSi2

Abstract Polycrystalline samples of UCoNiSi 2 and UNiCuSi 2 have been studied by X-ray diffraction at 295 K and ac susceptibility at 80–295 K. They have a ThCr 2 Si 2 -type crystallographic structureand order magnetically. UCoNiSi 2 undergoes an antiferromagnetic transition at 115K. UNiCuSi 2 undergoes three transitions at 162, 122 and 102 K to antiferromagnetic and ferro/ferrimagnetic phases.

The effect of non-magnetic dilution of the Tb sublattice in TbCo3B2.

Solid solutions of Tb(1-x)Y(x)Co(3)B(2) (x=0.05, 0.1, 0.25, 0.4 and 0.5) were studied by neutron powder diffraction, x-ray diffraction, AC susceptibility and SQUID magnetization measurements. Their magnetic and crystallographic properties were deduced and examined together with those previously published for the end compounds (x=0, 1). These solid solutions have hexagonal symmetry and are paramagnetic at RT, and undergo a magnetic ordering transition of the Co sublattice, with the magnetic moments along the hexagonal axis, at T(Co)∼150(15) K, independent of Y concentration. A second magnetic ordering transition of the Tb sublattice T(Tb)≤30 K accompanied by the rotation of the magnetic moments towards the basal plane, was observed for solid solutions with Y concentration x≤0.25. This transition was also found to be accompanied by a crystallographic symmetry decrease. Unexpectedly, neutron powder diffraction showed that the magnitude of the ordered magnetic moment of the Tb ion decreases with Tb concentration.

Magnetic properties of U(Ni1-xCux)2Si2 solid solutions in the vicinity of x = 0.50 studied by neutron diffraction and AC-susceptibility

Abstract The magnetic properties of two U(Ni 1−x Cu x ) 2 Si 2 solid solutions in the vicinity of x=0.50 (denoted I and II) have been studied by neutron diffraction and ac-susceptibility. Both materials have ThCr 2 Si 2 -type crystallographic structure. AC-susceptibility shows antiferromagnetic transitions at T N =150±5 K in UniCuSi 2 (I) and 155±5 K in UNiCuSi 2 (II), followed by several transitions with ferro/ferrimagnetic (F) character at lower temperatures. Apart from the transitions to AF-I structure (+−+−) at T N (150±1 K and 152±2 K, respectively), none of the F transitions is observed by neutron diffraction. Short-range magnetic order, involving several consecutive ferromagnetic planes or ferrimagnetic groups of planes in the AF-I phase, detected by ac-susceptibility and not by neutron diffraction in both materials and therefore significant to x∼0.50, is proposed to explain the unusual susceptibility.

Crystal structure and magnetic properties of DuY2BaCuO5 (u = 0.00, 0.61, 1.31)

Abstract Samples of D u Y 2 BaCuO 5 ( u =0.61, 1.31), were prepared by a direct reaction of the green phase (Y 2 BaCuO 5 ) with D 2 gas. The crystallographic structure of the three compounds ( u =0.00, 0.61, 1.31) were studied using X-ray and neutron powder diffraction. It was found that as D enters the green phase, a solid solution phase is formed with no symmetry change. Two sites partially occupied by D were determined. The occupancy of these sites is consistent with a maximum solubility of u =2. The temperature dependence of the magnetic susceptibility of the three samples obeyed the Curie-Weiss law with antiferromagnetic interaction. The paramagnetic Curie temperature decreased with deuteriding, while, the Cu + + magnetic moment remained unchanged.

Magnetic phase transition in YCo3B2 studied by magnetic resonance

Magnetic-susceptibility measurements, nuclear magnetic resonance (NMR) of B11, and electron magnetic-resonance (EMR) spectra of YCo3B2 were measured as a function of the temperature. The temperature dependence of the magnetic susceptibility showed a lambda-shaped anomaly at 150K. Whereas upon cooling, a shift in the resonance position of the NMR and EMR spectra is observed at 150K, marking the emergence of an internal magnetic field. The quadrupolar splitting of the NMR lines showed a marked discontinuity at 150K. The (T1T)−1∕2 values were found to be independent of temperature for T>175K, and to increase sharply upon cooling for T 160K is also found to increase markly upon cooling below 150K. All these effects are discussed and it is proposed that YCo3B2 undergoes a magnetic ordering phase transition at 150K.

Studies of the magnetic phase diagram of the U(Ni1−xCux)2Si2 system

Abstract Polycrystalline U(Ni 1− x Cu x ) 2 Si 2 solid solutions have a tetragonal ThCr 2 Si 2 type crystal structure. Antiferromagnetic (AF) transitions, observed by measurements of a.c. susceptibility for x = 0.10, 0.25, and 0.50, are confirmed by neutron diffraction. The AF structures are of type I (+ − + −) with k = (0,0,1) below T 0 = 108±5 K for x = 0.10 (with a possible incommensurate phase at 108–135 K), T N = 151±3 K for x = 0.25, and T N = 150±2 K for x = 0.50. The a.c. susceptibility transition for x = 0.75 is associated with the three magnetic structures observed by neutron diffraction: AF I, ferrimagnetic (+ + −) and AF IA (+ + − −), with k = (0,0,1), (0,0, 2 3 ) and (0,0, 1 2 ) , and T N = 120±3, 115±4 and 110±3 K respectively. Including previous neutron results on single-crystal UNi 2 Si 2 and powdered UCu 2 Si 2 , a magnetic phase diagram of the U(Ni 1− x Cu x ) 2 Si 2 system is proposed and discussed.

Paramagnetic properties of the (U1−xTbx)Co2Ge2 solid solutions

Abstract Polycrystalline (U 1− x Tb x )Co 2 Ge 2 solid solutions have the ThCr 2 Si 2 -type crystal structure and order antiferromagnetically. AC-susceptibility at 80–295 K yields paramagnetic Curie temperatures θ = −350±50, −15±5, −50±15, −12±5, and −80+5 K, and effective magnetic moments μ eff = 4.5, 5.9, 7.3, 8.5, and 12.0 (±0.5) μ B , for samples with x = 0, 0.25, 0.50, 0.75 and 1, respectively. The high μ eff values are related to occurrence of paramagnetic moments on U, Tb and Co, of which only U and Tb moments order magnetically.