J.B. Oliveira

Low temperature specific heat investigation of the mixed-valence regime in the laves system Ce(Co1−xNix)2

Abstract Heat capacity measurements of the system Ce(Co 1−xNi x ) 2 are consistent with a significant change in the valency of cerium above x ≈ 0.67. The composition dependence of γ is understood within Fermi liquid theory.

Dzyaloshinskii–Moriya nature of ferroelectric ordering in magnetoelectric Gd1−xYxMnO3 system

Abstract The phase diagram of Gd 1− x Y x MnO 3 , 0≤ x ≤0.4, is presented and the role of the driving mechanisms in stabilizing both magnetic and ferroelectric orderings is discussed in the framework of the Dzyaloshinskii–Moriya model. The ( x , T ) phase diagram reflects the effect of lattice distortions induced by the substitution of Gd 3+ ion by smaller Y 3+ ions, which gradually unbalances the antiferromagnetic against the ferromagnetic exchange interactions, enabling the emergence of ferroelectricity for higher concentrations of yttrium.

Determination of diffusion in electrodeposited CuNi compositionally-modulated multilayers based on magnetic measurements

Abstract The thermal stability in compositionally-modulated metallic multilayers (CMMs) is an important limitation towards their application. In the case of CMMs consisting of an alternation of magnetic and non-magnetic sublayers, the particular magnetic properties are destroyed by the diffusion between the sublayers. A method for the study of the diffusion in magnetic CMMs, based on the decrease in magnetisation with time and temperature, is presented. Systematic measurements of the magnetisation after proper heat treatment, by means of a Curie-Faraday microbalance, allow a complete characterisation of the diffusion process within the CMMs. Experimental results are presented on electrolytic Cuue5f8Ni CMMs with 100 nm thick sublayers. The value obtained for the activation energy agrees well with published data on diffusion of Cu in Ni obtained by radioactive measurements.

Thermomagnetic behaviour of quenched ribbons of Nd16Fe76B8

Abstract Magnetization and thermal demagnetization were studied on rapidly quenched ribbons. The thermomagnetic curves are explained on the basis of single-domain behaviour of non-interacting uniaxial particles described by the model of Stoner and Wohlfarth. There is a good qualitative agreement between theory and the experimental results confirming previous analysis of a Hopkinson effect in these samples.

High field differential susceptibility of the alloys Ce(Co1−xNix)2

Abstract The x dependence of the magnetic susceptibility χ (0) and of the coefficient γ of the linear term of the specific heat of the series Ce(Co 1− x Ni x ) 2 show a minimum around 0.67. This is possibly due to a crystal field effect. The high field differential susceptibility data reveals that the 4f electron of cerium is in a ‘ Γ 7 like’ state and that even if the valence of cerium is constant, χ(0) and γ would increase with x for x > 0.67.

Magnetic properties of the pseudobinary compounds NdxGd(1-x)Co2 (0 ⩽ x ⩽ 1)

Abstract Paramagnetic susceptibilities for compounds of the series NdxGd(1-x)Co2 (0 ⩽ x ⩽ 1), have been measured. The paramagnetic susceptibility and magnetic ordering temperature are discussed by means of an extended phenomenological theory; numerical analysis of the experimental data is presented. The behaviour of the cobalt paramagnetic susceptibility is inferred as a function of the alloy composition; the changes in saturation magnetisation and lattice parameter, with composition may be correlated with magnetic and heat capacity data.

Magnetic behavior in the Fe3Al1 system

The magnetic properties of the Fe3Al1 order‐disorder system have been investigated. Magnetization results of a rapildy cooled sample and susceptibility measurements show that the Curie temperature of the partially ordered B2 phase is 590u2009°C. Slow cooling experiments indicate the the Curie temperature of the fully ordered DO3 phase is about 520u2009°C. These temperatures are not consistent with either previously determined values or with the predictions of a phenomenological model. The magnetization value at 25u2009°C in high fields of the DO3 phase is significantly larger than previously observed values and is also larger than the magnetization of the B2 phase as expected from past investigations. The possible existence of a previously undetected antiferromagnetic phase seems to be indicated by the magnetization data at low temperatures and fields of the DO3 sample. The prominent anomaly in the temperature dependence of the magnetization at the B2‐DO3 order‐disorder temperature has been investigated and the resul...

Dynamics of a Sliding Ladder Leaning against a Wall.

This study is about the dynamics of a sliding ladder leaning against a vertical wall. The results are understood by considering the motion divided in two parts: (i) for with one degree of freedom, and (ii) for with two degrees of freedom, where the separation is determined by the instance when the ladder loses its contact with the wall. The observed experimental details are explained by appealing a simple model based on elementary notions of mechanics. We emphasize some features, such as a maximum of the x component of the velocity and of the acceleration of the centre of mass in the first part, and a minimum of the normal reaction force on the floor in the second.

Magnetic properties and Mössbauer studies of multiphase Nd–Fe–B alloy obtained from the dissociation of Nd2Fe14B melt spun ribbon

Abstract Nd 2 Fe 14 B crystallized from melt spun Nd 13 Fe 79 B 8 dissociates during high temperature controlled oxidation. The magnetic moment of the final system was measured from 1.7 to 1100xa0K under a magnetic field of 5 and 0.7xa0T, using a SQUID and a magnetic microbalance. The results show the formation of mainly Fe 3 B, Nd 2 O 3 and a third phase paramagnetic at room temperature. The dissociation of the Nd 2 Fe 14 B hard phase was followed by 57 Fe Mossbauer spectometry in addition to thermomagnetic measurements.