Magnetic skin effect in Pb(Fe _{1/2}$Nb _{1/2}$)O₃

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Relaxor-ferroelectrics exhibit unique dielectric properties due to random dipolar fields from chemical inhomogeneity.
• A macroscopic 'skin effect' is observed in relaxors, where near-surface properties differ significantly from the bulk.
• Pb(Fe_{1/2}Nb_{1/2})O₃ (PFN) is a multiferroic material with relaxor-like dielectric behavior and cluster spin-glass magnetic properties.

Purpose of the Study:

• To investigate the depth-dependent magnetic relaxation dynamics in PFN single crystals using muon spectroscopy.
• To determine if chemical concentration variations contribute to the observed magnetic relaxations.
• To explore the presence and nature of a magnetic 'skin effect' analogous to the structural skin effect in relaxors.

Main Methods:

• Variable momentum muon spectroscopy (positive muon spin relaxation) to probe magnetic relaxations at different depths.
• Negative muon elemental analysis to assess the concentration of Fe³⁺ and Nb⁵⁺ as a function of depth.
• Analysis of muon spin relaxation data using a stretched exponential model to characterize relaxation rate distributions.

Main Results:

• Zero-field positive muon spin relaxation in PFN is described by a stretched exponential, indicating a distribution of Fe³⁺ spin relaxation rates.
• The bandwidth of relaxation frequencies varies with muon momentum, confirming depth-dependent changes in Fe³⁺ relaxation dynamics.
• Negative muon elemental analysis showed minimal changes in Fe³⁺/Nb⁵⁺ concentration with depth, ruling out chemical inhomogeneity as the primary cause.

Conclusions:

• PFN exhibits a magnetic 'skin effect' where magnetic relaxation dynamics are depth-dependent.
• This magnetic skin effect is not attributable to variations in chemical composition.
• The findings suggest an analogy between the structural skin effect in relaxors and the observed magnetic behavior in PFN.