The magnetic ground state of CaMn2Sb2

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Abstract

We have determined the ground state of the layered compound CaMn2Sb2 which crystalizes in the CaAl2Si2 structure. We have performed specific heat and neutron powder diffraction measurements at different temperatures. The neutron powder diffraction results reveal that the system orders antiferromagnetically at 88 K which agrees with the specific heat measurements. The ground state magnetic structure is consistent with previous theoretical calculations.

Introduction

The AM2X2 ternary intermetallic (A=rare or alkaline earth, M=transitionmetal, X=Si,Ge,P,As,Sb) compounds have revealed interesting magnetic properties due to the interplay between their magnetic sublattices [1]. The most abundant structure of these materials is the ThCr2Si2-type, and special attention has been paid to those with M=Mn. In these systems, the in-plane Mn–Mn distance determines their magnetic structure [2]. In particular, the manganese silicides and manganese germanides are special cases of the latter compounds and for example, AMn2(Si,Ge)2-alloys studies have found antiferromagnetic ordering of the Mn ions, which is concordance with the lower in-plane Mn–Mn distance as compared to the critical value necessary for the stabilization of antiferromagnetic ordering [3], [4].

However, other AM2X2 ternary systems, instead, crystallize in the CaAl2Si2-type structure [5], [6], and it has recently been found that some of these compounds have complex magnetic structures. Neutron diffraction and magnetic measurements revealed that the SrMn2P2 system orders antiferromagnetically and that frustration effects are present [7]. On the other hand, in the EuMn2P2 system [8], the Eu spins align ferromagnetically in the plane with these planes coupled antiferromagnetically along the c-axis at about 16.5 K.

It was suggested that the substitution of P and As ions by larger Sb atoms in the AMn2(P,As)2 series should modify the Mn–Mn distance and thus change their magnetic properties [9]. Following this idea, YbMn2Sb2 was shown to be magnetically ordered with a complex magnetic ordering of the Mn ions [9].

Recently, (Ca,Sr)Mn2Sb2 intermetallic compounds were studied, where the CaMn2Sb2 compound showed magnetic order, with a possible antiferromagnetic coupling between the magnetic moments of the two Mn-ions sublattices [10]. In this work we show neutron diffraction and thermal measurements performed on single crystals and powders of CaMn2Sb2, which clarify the magnetism of this compound.

Section snippets

Experimental

The CaMn2Sb2 single-crystals were grown using Sn as a flux. High purity starting materials (higher than 99.9%) were sealed in vacuum and heated to 1273 K for 48 h. Thereafter, the temperature was decreased to 773 K (cooled at 10C/h) where the molten flux was removed by centrifugation. X-ray diffraction performed using a Bruker SMART CCD [11] diffractometer verified that the structure can be described as double corrugate layers of Mn2Sb2- separated by Ca2+ planes. The unit cell parameters at room

Results and discussion

We started our exploration of this compound with specific heat measurements. In Fig. 1, C/T is plotted as a function of temperature, where C includes contributions from electronic, phonon and magnetic terms. In the figure, it can be noted that there is only one sharp feature, which is a peak at T83K. This would suggest that the true temperature of the magnetic phase transition in this compound is much lower than previously suspected. To further investigate the nature of this transition, we

Acknowledgments

The authors thank Dr. S. Bobev and Dr. M. Massalami for supply the samples used in this study. A.M.G. and J.L.G. acknowledge the financial support of the Brazilian agencies CNPq and FAPERJ.

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