Anomalous behavior of the magnetic hyperfine field at 140Ce impurities at La sites in LaMnSi2

C Domienikan,A W Carbonari,B Bosch-Santos,R N Saxena,G A Cabrera-Pasca

doi:10.1063/1.5006897

Abstract

Magnetic hyperfine field has been measured in the orthorhombic intermetallic compound LaMnSi2 with perturbed angular correlation (PAC) spectroscopy using radioactive 140La(140Ce) nuclear probes. Magnetization measurements were also carried out in this compound with MPSM-SQUID magnetometer. Samples of LaMnSi2 compound were prepared by arc melting the component metals with high purity under argon atmosphere followed by annealing at 1000°C for 60 h under helium atmosphere and quenching in water. X-ray analysis confirmed the samples to be in a single phase with correct crystal structure expected for LaMnSi2 compound. The radioactive 140La (T1/2 = 40 h) nuclei were produced by direct irradiation of the sample with neutrons in the IEA-R1 nuclear research reactor at IPEN with a flux of ∼ 1013 n cm−2s−1 for about 3 - 4 min. The PAC measurements were carried out with a six BaF2 detector spectrometer at several temperatures between 10 K and 400 K. Temperature dependence of the hyperfine field, Bhf was found to be anomalous. A modified two-state model explained this anomalous behavior where the effective magnetic hyperfine field at 140Ce is believed to have two contributions, one from the unstable localized spins at Ce impurities and another from the magnetic Mn atoms of the host. The competition of these two contributions explains the anomalous behavior observed for the temperature dependence of the magnetic hyperfine field at 140Ce. The ferromagnetic transition temperature (TC) of LaMnSi2 was determined to be 400(1) K confirming the magnetic measurements.

Highlights

A series of intermetallic compounds RMnSi2, where R is a rare earth element, crystallize in an orthorhombic TbFeSi2-type structure belonging to space group (Cmcm)
In this work we report on the results of temperature dependence of magnetic hyperfine field (Bhf ) in LaMnSi2 measured by Perturbed Angular Correlation (PAC) spectroscopy using 140La(140Ce) nuclear probe
The LaMnSi2 samples were analyzed by powder X-ray diffraction and the spectra were refined with Rietveld method using Rietica software.[14]

Summary

Introduction

A series of intermetallic compounds RMnSi2, where R is a rare earth element, crystallize in an orthorhombic TbFeSi2-type structure belonging to space group (Cmcm). This structure can be described as built on alternating (010) planes containing R, Mn and Si atoms in a sequence Mn-Si-R-Si-Si-R-Si-Mn. Between each Mn-layer six nonmagnetic layers are sandwiched. Between each Mn-layer six nonmagnetic layers are sandwiched This structure is closely related to the tetragonal ThCr2Si2-type structure of RMn2(Si, Ge)[2] compounds which have been studied by different techniques.[1,2,3,4,5] The much less studied RMnSi2 compounds have been investigated in the past by X-ray and neutron diffraction,[6] magnetization[7,8] and perturbed angular correlation (PAC) measurements using 111Cd probe.[9] In these compounds, the Mn sub-lattice orders ferromagnetically up to high temperatures with TC values well above room temperature.

Methods

Results

Conclusion