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Title: Size-dependent magnetic ordering and spin-dynamics in DyPO4 and GdPO4 nanoparticles

Abstract

Low-temperature magnetic susceptibility and heat capacity measurements on nanoparticles (d 2.6 nm) of the antiferromagnetic compounds DyPO4 (TN = 3:4 K) and GdPO4 (TN = 0:77 K) provide clear demonstrations of finite-size effects, which limit the divergence of the magnetic correlation lengths, thereby suppressing the bulk long-range magnetic ordering transitions. Instead, the incomplete antiferromagnetic order inside the particles leads to the formation of net magnetic moments on the particles. For the nanoparticles of Ising-type DyPO4 superparamagnetic blocking is found in the ac-susceptibility at 1 K, those of the XY-type GdPO4 analogue show a dipolar spin-glass transition at 0:2 K. Monte Carlo simulations for the magnetic heat capacities of both bulk and nanoparticle samples are in agreement with the experimental data. Strong size effects are also apparent in the Dy3+ and Gd3+ spin-dynamics, which were studied by zero-field SR relaxation and high-field 31P-NMR nuclear relaxation measurements. The freezing transitions observed in the ac-susceptibility of the nanoparticles also appear as peaks in the temperature dependence of the zero-field SR rates, but at slightly higher temperatures - as to be expected from the higher frequency of the muon probe. For both bulk and nanoparticles of GdPO4, the muon and 31P-NMR rates are formore » T 5 K dominated by exchange-narrowed hyperfine broadening arising from the electron spin-spin interactions inside the particles. The dipolar hyperfine interactions acting on the muons and the 31P are, however, much reduced in the nanoparticles. For the DyPO4 analogues the high-temperature rates appear to be fully determined by electron spin-lattice relaxation processes.« less

Authors:
 [1];  [2];  [2];  [3];  [3];  [4];  [5];  [6];  [2]
  1. Instituto de Ciencia de Materiales de Aragon (ICMA), Spain
  2. Leiden University
  3. ISIS Facility, Rutherford Appleton Laboratory
  4. Universidad de Malaga, Spain
  5. University of Osnabruck, Barbarastr Germany
  6. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1024699
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Journal Article
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 94; Journal Issue: 9; Journal ID: ISSN 1098--0121
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ELECTRONS; FREEZING; J-J COUPLING; MAGNETIC MOMENTS; MAGNETIC SUSCEPTIBILITY; MUON PROBES; MUONS; RELAXATION; SPECIFIC HEAT; SPIN-LATTICE RELAXATION; TEMPERATURE DEPENDENCE

Citation Formats

Evangelisti, Marco, Sorop, Tibi G, Bakharev, Oleg N, Visser, Dirk, Hillier, Adrian D., Alonso, Juan, Haase, Markus, Boatner, Lynn A, and De Jongh, L. Jos. Size-dependent magnetic ordering and spin-dynamics in DyPO4 and GdPO4 nanoparticles. United States: N. p., 2011. Web. doi:10.1103/PhysRevB.84.094408.
Evangelisti, Marco, Sorop, Tibi G, Bakharev, Oleg N, Visser, Dirk, Hillier, Adrian D., Alonso, Juan, Haase, Markus, Boatner, Lynn A, & De Jongh, L. Jos. Size-dependent magnetic ordering and spin-dynamics in DyPO4 and GdPO4 nanoparticles. United States. doi:10.1103/PhysRevB.84.094408.
Evangelisti, Marco, Sorop, Tibi G, Bakharev, Oleg N, Visser, Dirk, Hillier, Adrian D., Alonso, Juan, Haase, Markus, Boatner, Lynn A, and De Jongh, L. Jos. Sat . "Size-dependent magnetic ordering and spin-dynamics in DyPO4 and GdPO4 nanoparticles". United States. doi:10.1103/PhysRevB.84.094408.
@article{osti_1024699,
title = {Size-dependent magnetic ordering and spin-dynamics in DyPO4 and GdPO4 nanoparticles},
author = {Evangelisti, Marco and Sorop, Tibi G and Bakharev, Oleg N and Visser, Dirk and Hillier, Adrian D. and Alonso, Juan and Haase, Markus and Boatner, Lynn A and De Jongh, L. Jos},
abstractNote = {Low-temperature magnetic susceptibility and heat capacity measurements on nanoparticles (d 2.6 nm) of the antiferromagnetic compounds DyPO4 (TN = 3:4 K) and GdPO4 (TN = 0:77 K) provide clear demonstrations of finite-size effects, which limit the divergence of the magnetic correlation lengths, thereby suppressing the bulk long-range magnetic ordering transitions. Instead, the incomplete antiferromagnetic order inside the particles leads to the formation of net magnetic moments on the particles. For the nanoparticles of Ising-type DyPO4 superparamagnetic blocking is found in the ac-susceptibility at 1 K, those of the XY-type GdPO4 analogue show a dipolar spin-glass transition at 0:2 K. Monte Carlo simulations for the magnetic heat capacities of both bulk and nanoparticle samples are in agreement with the experimental data. Strong size effects are also apparent in the Dy3+ and Gd3+ spin-dynamics, which were studied by zero-field SR relaxation and high-field 31P-NMR nuclear relaxation measurements. The freezing transitions observed in the ac-susceptibility of the nanoparticles also appear as peaks in the temperature dependence of the zero-field SR rates, but at slightly higher temperatures - as to be expected from the higher frequency of the muon probe. For both bulk and nanoparticles of GdPO4, the muon and 31P-NMR rates are for T 5 K dominated by exchange-narrowed hyperfine broadening arising from the electron spin-spin interactions inside the particles. The dipolar hyperfine interactions acting on the muons and the 31P are, however, much reduced in the nanoparticles. For the DyPO4 analogues the high-temperature rates appear to be fully determined by electron spin-lattice relaxation processes.},
doi = {10.1103/PhysRevB.84.094408},
journal = {Physical Review B},
issn = {1098--0121},
number = 9,
volume = 94,
place = {United States},
year = {2011},
month = {1}
}