Successive magnetic transitions in TbNiAl2 studied by neutron diffraction

D P Rojas,J Rodríguez Fernández,J Sánchez Marcos

doi:10.1088/1742-6596/549/1/012020

Abstract

We report measurements of DC (AC) magnetic susceptibility and neutron diffraction on TbNiAl2 alloy. The Rietveld refinements of the x-ray and neutron diffraction data are consistent with an orthorhombic structure of the type MgCuAl2 (space group Cmcm). The results of DC (AC)- magnetic susceptibility show two successive magnetic transitions at 20 K and 11.7 K with antiferromagnetic and ferromagnetic (or ferrimagnetic) features, respectively. On the other hand, neutron diffraction patterns show that, below 20 K and down to 12 K, new reflexions appear, confirming the antiferromagnetic character of the transition observed in the macroscopic measurements. Also, at least one of these new reflexions, located at Q = 1.2 Å−1, shifts to higher angles when the temperature decreases, indicating an incommensurate magnetic structure. Below 11 K, many reflexions disappear and new reflexions increase, evidencing a new magnetic transition.

Highlights

Tb intermetallic compounds have been extensively studied from both fundamental and applied points of view because their exotic magnetic behaviours and the interesting properties they show, associated for instance, with the magnetocaloric effect [1]
The field dependence of the isothermal magnetization at 2, 12 K and 17 K, shows a full saturation at the highest achieved magnetic field of 90 kOe, with values of 7.02 μB (2 and 12 K) and 6.75 μB (17 K) still far from the expected gJ value of 9 μB for the full multiplet of Tb3+ (g=3/2, J =6), which could be attributed to crystalline field effects
In (χ ), a peak around 11.7 K appears, whereas at 20 K a second tiny anomaly develops for 5 kHz. As it is well known the peak in χ is commonly associated to dynamic processes of domain movements, whereas the increase of the absolute value of χ for 5 kHz can be attributed to a contribution to the susceptibility arising from currents induced in the sample by the alternating magnetic field, as observed in other intermetallic systems [8]

Summary

Introduction

Tb intermetallic compounds have been extensively studied from both fundamental and applied points of view because their exotic magnetic behaviours and the interesting properties they show, associated for instance, with the magnetocaloric effect [1]. In TbNiAl4 antiferromagnetic (AFM) transitions, in zero applied magnetic field, were observed at 28 and 34 K. The magnetic structure of the lowest temperature phase is AFM with a (0 1 0) propagation vector, as obtained from neutron diffraction [5].

Results

Conclusion