Magnetic field and temperature dependence of the amplitude-modulated magnetic structure ofPrNi2Si2determined by single-crystal neutron diffraction

J A Blanco,D Schmitt,M Rotter,J Campo,B Fåk,J A Rodríguez-Velamazán,B Grenier,P Lejay,E Ressouche

doi:10.1103/physrevb.82.054414

Abstract

The temperature and magnetic field dependence of the magnetic structure in the singlet crystal-field ground-state system ${\text{PrNi}}_{2}{\text{Si}}_{2}$ have been determined using single-crystal neutron diffraction. At the magnetic ordering temperature in zero field, ${T}_{N}=20.0\ifmmode\pm\else\textpm\fi{}0.5\text{ }\text{K}$, an amplitude-modulated magnetic structure sets in with a propagation vector $\mathbf{k}=(0,0,0.87)$ and the magnetic moments of the ${\text{Pr}}^{3+}$ ions parallel to the $c$ axis of the body-centered tetragonal structure. The magnetic structure remains amplitude modulated down to low temperatures $(T=1.6\text{ }\text{K})$ with only a small tendency to squaring up, as signaled by the weak intensity of the third harmonic that develops below 16 K. With applied field along the easy axis, the modulated structure goes smoothly over into a ferromagnetic state. At the critical field of ${H}_{c}=58\text{ }\text{kOe}$, the first harmonic disappears and the field-induced ferromagnetic moment shows a kink, in agreement with magnetization measurements. Both the temperature and magnetic field dependence are well described by a periodic field Hamiltonian including magnetic exchange and the crystalline electric field.

Highlights

Frustration in magnetic systems occurs when the interaction energies cannot be simultaneously minimized.[1,2,3] This may arise from the topology of the latticegeometric frustrationor from competing magnetic interactions
Our single-crystal neutron-diffraction measurements clearly establish that the magnetic propagation vector is k = ͑0, 0, 0.870͒, in agreement with earlier powder neutron diffraction results.[10]
Using single-crystal neutron diffraction, we have shown that the amplitude-modulated magnetic structure that develops below TN = 20 K in PrNi2Si2 remains essentially sinusoidal down to the lowest temperatures, with only a very weak third harmonic, m3k / mk ϳ 1 / 7, at T = 1.6 K

Summary

INTRODUCTION

Frustration in magnetic systems occurs when the interaction energies cannot be simultaneously minimized.[1,2,3] This may arise from the topology of the latticegeometric frustrationor from competing magnetic interactions. If the system has a strong easy-axis anisotropy due to crystal field effects, the resulting magnetic structure may be amplitude modulated, i.e., the size of the ordered magnetic moment varies from one site to the next. If the system has a strong easy-axis anisotropy due to crystal field effects, the resulting magnetic structure may be amplitude modulated, i.e., the size of the ordered magnetic moment varies from one site to the Such magnetic structures are not stable down to zero temperature since it is not entropically favorable for a doublet ground state to have zero ordered magnetic moment on some of the sites. We have measured the magnetic field dependence of the magnetic structure with H ʈ c in order to test predictions of model calculations.[12,13]

EXPERIMENTAL

RESULTS

ANALYSIS

CONCLUSION