A Señas

Three-dimensional magnetic ordering in the Rb2CuCl4 layer perovskite—structural correlations

This work investigates the magnetic structure of Rb2CuCl4 as a function of pressure and temperature using neutron diffraction. As in most A2CuCl4 layered perovskites, there is a 2D ferromagnetic order within the layers. This behaviour is due to the Jahn–Teller (JT) antiferrodistortive structure of the CuCl6 units. Rb2CuCl4 undergoes a 3D magnetic transition at TN = 16 K, which mainly depends on the weak antiferromagnetic interlayer interaction. The pressure slightly increases TN ,a s∂TN/∂P = 0.13 K kbar −1 .T his behaviour is interpreted in terms of pressure-induced tilts and reduction of interlayer distance, both effects increasing the antiferromagnetic exchange coupling between layers. The results are compared with previous magnetic studies under chemical and hydrostatic pressure along layered perovskites series of [CnH2n+1NH3]2CuCl4 (n = 1–3) and BMnF4 (B = Li, Na, K, Rb, Tl, Cs and NH4 )i nvol ving JT ions of Cu 2+ and Mn 3+ ,r esp ectively. We show that the ratio of the interlayer to intralayer coupling, and thus the nature of the magnetic order, can be tuned by chemical or hydrostatic pressure along the A2CuCl4 series. The present findings stress the relevance of octahedral tilts on the magnetic behaviour of layered perovskites.

Inhomogeneous spin glass and mixed phases in cerium compounds

Abstract We discuss the properties of the spin glass phase observed in the CeNi 1− x Cu x system. We have measured the AC susceptibility, field cooled and zero field cooled magnetization, hysteresis loops, magnetic relaxation and neutron scattering. An inhomogeneous magnetic arrangement, namely spin glass-like state, is proposed. A description consisting of nanometric magnetic clusters embedded in a non-magnetic matrix is likely for the richer Ni compounds. We support this hypothesis as a consequence of the coexistence of chemical disorder in the Ni/Cu crystallographic sites, the random and coherent anisotropy, the competing magnetic interactions and large 4f-conduction band hybridization.

Pressure Dependence on the Magnetic Structures of TbNi 1−x Cu x ( x =0.3 & 0.4) Using Neutron Techniques

In the TbNi 1 m x Cu x series, the Cu substitution has two main effects: the increase of the cell volume (∼4.3% from TbNi to TbCu), and the increasing importance of antiferromagnetic interactions. In this sense, the magnetic structures of these compounds evolve from a non-collinear ferromagnetic (FM) arrangement to an incommensurate antiferromagnetic (AFM) one for Cu concentration larger than 35%. In this paper, we present the effects of pressure on the magnetic structures of the compounds which are closer to this critical concentration: TbNi 0.7 Cu 0.3 (FM) and TbNi 0.6 Cu 0.4 (AFM). It appears that a global antiferromagnetic behaviour is favoured by pressure.

Multiphase magnetic analysis through the martensitic transition of TbCu

Abstract We present the neutron diffraction data obtained from both TbCu bulk and powdered samples. This binary alloy undergoes a martensitic transition evolving from a cubic CsCl-type of structure at room temperature to a mixture of cubic and orthorhombic phases at low temperatures. The multiphase Rietveld refinement has been improved due to the specific behaviour of the powdered samples, which do not suffer this transition keeping the same cubic structure along the full temperature range. This combined analysis, which has already been applied with success to GdCu, has allowed us to obtain precise information about the nature of the martensitic transition and the magnetic structure of both the cubic and the orthorhombic phases.

Complex magnetic structures in TbPt1−xCux compounds

Abstract We present neutron diffraction measurements in TbPt 1− x Cu x for x =0, 0.2, 0.4, 0.6 and 0.8 samples. TbPt shows a ferromagnetic non-collinear-C x F z structure. The Cu substitution modifies the conduction band inducing amplitude modulated (AM) structures. For x =0.2 and 0.4, these AM phases coexist with the ferromagnetic ones while for x =0.6 and 0.8 only AM structures are observed.

TbPt0.7Cu0.3: A Critical Ferro–Antiferromagnetic Compound Studied under Pressure

We report the effects of pressure up to 8 kbar on the magnetic measurements (magnetization and susceptibility) on the TbPt 0.7 Cu 0.3 compound, which is precisely the critical composition between ferro and antiferromagnetic behaviour in the TbPt 1- x Cu x series. The effect of pressure on the magnetization and susceptibility is quite small up to 8 kbar. Neutron diffraction experiments up to 42 kbar show appreciable effects on the magnetic structure. From the neutron diffraction analysis a shift to higher temperatures of Curie and Neel temperatures is shown at 22 and 42 kbar. The low temperature ferromagnetic non collinear structure (-CxFz) has undergone no modification while an increase of the magnetic periodicity in the incommensurate magnetic structure is also observed.

Three-dimensional magnetic ordering in the Rb2CuCl4layer perovskite-structural correlations

This work investigates the magnetic structure of Rb2CuCl4 as a function of pressure and temperature using neutron diffraction. As in most A2CuCl4 layered perovskites, there is a 2D ferromagnetic order within the layers. This behaviour is due to the Jahn–Teller (JT) antiferrodistortive structure of the CuCl6 units. Rb2CuCl4 undergoes a 3D magnetic transition at TN = 16 K, which mainly depends on the weak antiferromagnetic interlayer interaction. The pressure slightly increases TN ,a s∂TN/∂P = 0.13 K kbar −1 .T his behaviour is interpreted in terms of pressure-induced tilts and reduction of interlayer distance, both effects increasing the antiferromagnetic exchange coupling between layers. The results are compared with previous magnetic studies under chemical and hydrostatic pressure along layered perovskites series of [CnH2n+1NH3]2CuCl4 (n = 1–3) and BMnF4 (B = Li, Na, K, Rb, Tl, Cs and NH4 )i nvol ving JT ions of Cu 2+ and Mn 3+ ,r esp ectively. We show that the ratio of the interlayer to intralayer coupling, and thus the nature of the magnetic order, can be tuned by chemical or hydrostatic pressure along the A2CuCl4 series. The present findings stress the relevance of octahedral tilts on the magnetic behaviour of layered perovskites.

Three-dimensional magnetic ordering in theRb2CuCl4 layer perovskite—structural correlations

This work investigates the magnetic structure of Rb2CuCl4 as a function of pressure and temperature using neutron diffraction. As in most A2CuCl4 layered perovskites, there is a 2D ferromagnetic order within the layers. This behaviour is due to the Jahn–Teller (JT) antiferrodistortive structure of the CuCl6 units. Rb2CuCl4 undergoes a 3D magnetic transition at TN = 16 K, which mainly depends on the weak antiferromagnetic interlayer interaction. The pressure slightly increases TN ,a s∂TN/∂P = 0.13 K kbar −1 .T his behaviour is interpreted in terms of pressure-induced tilts and reduction of interlayer distance, both effects increasing the antiferromagnetic exchange coupling between layers. The results are compared with previous magnetic studies under chemical and hydrostatic pressure along layered perovskites series of [CnH2n+1NH3]2CuCl4 (n = 1–3) and BMnF4 (B = Li, Na, K, Rb, Tl, Cs and NH4 )i nvol ving JT ions of Cu 2+ and Mn 3+ ,r esp ectively. We show that the ratio of the interlayer to intralayer coupling, and thus the nature of the magnetic order, can be tuned by chemical or hydrostatic pressure along the A2CuCl4 series. The present findings stress the relevance of octahedral tilts on the magnetic behaviour of layered perovskites.