Moshe Kuznietz

The magnetic phase diagram of the UAS1-xSex system studied by neutron diffraction from single crystals

Abstract The magnetic phase diagram of the UAs 1- x Se x system (temperature versus composition) has been determined from neutron diffraction measurements in zero applied magnetic field on single crystals with x =0.03, 0.05, 0.10, 0.20, 0.25, 0.30, 0.40 and 0.50, as well as from measurements in finite applied magnetic fields on single crystals with x =0.10, 0.20, 0.25 and 0.30. For x ⩽0.40 an incommensurate magnetic ordering ( k =[0,0, k ]; m k ∥ k ) develops below T N down to T IC . The k - value at T N decreases with the increase of x ; in decreasing temperatures the k -value approaches the commensurate value below T IC . At T IC an incommensurate-commensurate transition leads to the type-I phase ( k =1) for x ⩽0.05 (with a subsequent transition to type-IA at T O ), to the type-IA phase ( k= 1 2 ) for 0.05 ⩽ x ⩽ 0.30, and to the squaring-up of the (5+,4-) phase ( k ≈0.244) for x =0.40 below T ≈90 K. For x ⩽0.50 the ordering is ferromagnetic. The nature of the multi- k structure is determined from measurements in finite fields. With the previously established single- k structure of type-I (in UAs), the UAs 1- x Se x system exhibits single- k , double- k and triple- k structures. A double- k -triple- k transition occurs for x ≈0.15 in the type-IA phase and for x ≈0.22 in the incommensurate phase. The ordered magnetic moment at T =4.2 K is practically independent of the ordering ( m ≈2μ B ).

Single crystal investigation of the magnetic phase diagram of Up-Us

Abstract Neutron diffraction investigations were performed on single crystals of UP 0.80 S 0.20 and UP 0.75 S 0.25 . An incommensurate phase is observed in UP 0.80 S 0.20 below T N . A commensurate (5+,5-) structure occurs in UP 0.75 S 0.25 below T ≈ 50 K. The above new phases cause several changes in the UP-US magnetic phase diagram, proposed previously, based on powder results. The amended diagram is presented.

Neutron diffraction investigation of commensurate and incommensurate phases in UAs1-xSex single crystals

The magnetic phases of the UAs1-xSex single crystals were investigated by neutron diffraction. For x ⩽ 0.40 an incommensurate antiferromagnetic ordering (k = [00k];mk|k) is observed below TN down to TIC. At TN the k-value varies continuously with x; in decreasing temperature the k-value approaches the commensurate value below TIC. At TIC an incommensurate-commensurate transition leads to type-IA (k = 0.500) for 0.05 < x ⩽ 0.30, to type-I (k = 1) for x ⩽ 0.05 (with subsequent transition to type-IA), and to squaring-up of (5+, 4-) structure for x = 0.40. For x ≳ 0.50 the ordering is ferromagnetic.

Magnetism of the series UFexAl12−x

Abstract Recent results from low-temperature specific heat and magnetization measurements performed on crystals of UFe x Al 12− x (3.8 x

Evolution of magnetism in the UFexAl12−x intermetallic series

Single crystals of UFexAl12−x for 4<x<5 were studied by magnetization and specific heat measurements. Based on these results, the evolution of magnetism in this series is discussed.

Neutron diffraction study of UAs0.95Se0.05 single crystal disappearance of the type-I antiferromagnetic structure

Abstract A single crystal of UAs 0.95 Se 0.05 has been studied by neutron diffraction. It orders at T N = 121.5 K with an incommensurate phase, characterized by a wavevector k = [00k] with k ( T N ) = 0.619. On lowering the temperature, two different magnetic behaviours are observed. First an incommensurate-commensurate transition at T IC = 106 K to the type-I antiferromagnetic phase (+ - + -), with k ( T IC ) = 0.596, is followed by a transition at T 0 = 93 K to the type-IA atiferromagnetic phase (+ + - -). The second one corresponds to an incommensurate phase which transforms directly to type-IA at T IC = 103 K. These behaviours determine the critical composition, x ≈ 0.05, for the disappearance of the type-I structure in the arsenic-rich UAs 1 - x Se x solid solutions. The magnetic phase diagram in this region is established and compared with previous versions.

Neutron diffraction and magnetization studies of the magnetic phase diagram of UAs0.75Se0.25 single crystal

Abstract Single crystals of UAs 0.75 Se 0.25 have been investigated by neutron diffraction and magnetization in magnetic fields up to 67.2 and 190 kOe, respectively, applied along the cubic [001] axis. In H = 0 UAs 0.75 Se 0.25 orders antiferromagnetically at T N = 126 K in an incommensurate phase, exhibiting “anomalous” k -range behaviour above T IC = 96 K. Below T IC the crystal acquires the commensurate type-IA phase. Both phases have the triple- k structure. Above H = 15 kOe two incommensurate components ( k x and k y ) perpendicular to the field together with a ferromagnetic component ( k z ) along the field direction develop below T N , undergoing a transition at T 0 to the incommensurate triple- k structure ( k x = k y = k z ). This phase has a direct transition at T IC to the triple- k type-IA phase for H ⪅ 25 kOe. In higher fields the transition occurs in two steps: the perpendicular components of the wavevector k ( k x and k y ) undergo a transition to the commensurate k x = k y = 1 2 values at T IC ⊥ , while the parallel component ( k z ) remains incommensurate. The latter undergoes a transition to the commensurate k z = 1 2 value at T IC ∥ ( T > IC ⊥ ), thereby completing the transition to the triple- k type-IA phase. All mentioned transitions and phases are included in the proposed magnetic phase diagram (magnetic field versus temperature) of UAs 0.75 Se 0.25 .

Magnetic features of the (U0.50Tm0.50)Ni2B2C solid solution

Abstract The quaternary borocarbides TmNi 2 B 2 C and UNi 2 B 2 C crystallize in the body-centered tetragonal LuNi 2 B 2 C-type structure, and exhibit antiferromagnetic order below 1.53 and 218 K, respectively. The magnetic structure of TmNi 2 B 2 C is characterized by incommensurate, long-range, spin-density-wave in the basal plane, with Tm moments along the c -axis, and does not involve ferromagnetic basal planes, while that of UNi 2 B 2 C is assumed to contain U moments along the c -axis in ferromagnetic basal planes. In the system (U,Tm)Ni 2 B 2 C the different magnetic structures of the end compounds result in a frustration of magnetic moments, which is not just directional. Indeed, the newly-prepared intermediate solid solution (U 0.50 Tm 0.50 )Ni 2 B 2 C is paramagnetic down to 2 K, for both as-cast and annealed samples, with no indication for any cooperative phenomenon. The paramagnetic values of the annealed sample [ θ =−5.6(5) K, μ eff =5.4(1) μ B ] are compatible with those of the end compounds.