Details
| Original language | English |
|---|---|
| Pages (from-to) | 5801-5812 |
| Number of pages | 12 |
| Journal | Nanoscale Advances |
| Volume | 3 |
| Issue number | 20 |
| Early online date | 13 Aug 2021 |
| Publication status | Published - 21 Oct 2021 |
| Externally published | Yes |
Abstract
Magnetite nanoparticles (MNPs) with 12, 34 and 53 nm sizes have been measured by AC-magnetometry at 50 kHz and 57 mT maximum applied field. The MNPs form chains under the AC-field, and the dynamics of the formation can be studied by measuring hysteresis cycles at different times. The measurement time has been varied from 5 ms to 10 s and for different initial temperatures of 5, 25 and 50 °C. The chain formation, identified by the increase of susceptibility and remanence with the measurement time, appears only for 34 nm particles. It has been observed that saturation, remanence and susceptibility at low (high) fields increase (decrease) with time. For the other two samples, these magnitudes are independent of time. At low fields, the heating efficiency is higher at 5 °C than at 50 °C, whereas it shows an opposite behaviour at higher fields; the origin of this behaviour is discussed in the article. Additionally, the relaxation times,τ Nandτ B, have been calculated by considering the influence of the applied field. Chain formation requires translation and rotation of MNPs; therefore, the Brownian mechanism plays a fundamental role. It is found that magnetic reversal for 12 nm MNPs is mainly due to Néel relaxation. However, in the case of 34 nm MNPs, both mechanisms, Néel and Brownian relaxation, can be present depending on the amplitude of the field; forμ 0H< 22 mT, the physical rotation of the particle is the dominant mechanism; on the other hand, forμ 0H> 22 mT, both mechanisms are present within the size distribution. This highlights the importance of taking the field intensity into account to calculate relaxation times when analysing the relaxation mechanisms of magnetic colloids subjected to AC fields.
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In: Nanoscale Advances, Vol. 3, No. 20, 21.10.2021, p. 5801-5812.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Time-dependent AC magnetometry and chain formation in magnetite
T2 - The influence of particle size, initial temperature and the shortening of the relaxation time by the applied field
AU - Morales, Irene
AU - Costo, Rocio
AU - Mille, Nicolas
AU - Carrey, Julian
AU - Hernando, Antonio
AU - de la Presa, Patricia
N1 - Publisher Copyright: © The Royal Society of Chemistry 2021.
PY - 2021/10/21
Y1 - 2021/10/21
N2 - Magnetite nanoparticles (MNPs) with 12, 34 and 53 nm sizes have been measured by AC-magnetometry at 50 kHz and 57 mT maximum applied field. The MNPs form chains under the AC-field, and the dynamics of the formation can be studied by measuring hysteresis cycles at different times. The measurement time has been varied from 5 ms to 10 s and for different initial temperatures of 5, 25 and 50 °C. The chain formation, identified by the increase of susceptibility and remanence with the measurement time, appears only for 34 nm particles. It has been observed that saturation, remanence and susceptibility at low (high) fields increase (decrease) with time. For the other two samples, these magnitudes are independent of time. At low fields, the heating efficiency is higher at 5 °C than at 50 °C, whereas it shows an opposite behaviour at higher fields; the origin of this behaviour is discussed in the article. Additionally, the relaxation times,τ Nandτ B, have been calculated by considering the influence of the applied field. Chain formation requires translation and rotation of MNPs; therefore, the Brownian mechanism plays a fundamental role. It is found that magnetic reversal for 12 nm MNPs is mainly due to Néel relaxation. However, in the case of 34 nm MNPs, both mechanisms, Néel and Brownian relaxation, can be present depending on the amplitude of the field; forμ 0H< 22 mT, the physical rotation of the particle is the dominant mechanism; on the other hand, forμ 0H> 22 mT, both mechanisms are present within the size distribution. This highlights the importance of taking the field intensity into account to calculate relaxation times when analysing the relaxation mechanisms of magnetic colloids subjected to AC fields.
AB - Magnetite nanoparticles (MNPs) with 12, 34 and 53 nm sizes have been measured by AC-magnetometry at 50 kHz and 57 mT maximum applied field. The MNPs form chains under the AC-field, and the dynamics of the formation can be studied by measuring hysteresis cycles at different times. The measurement time has been varied from 5 ms to 10 s and for different initial temperatures of 5, 25 and 50 °C. The chain formation, identified by the increase of susceptibility and remanence with the measurement time, appears only for 34 nm particles. It has been observed that saturation, remanence and susceptibility at low (high) fields increase (decrease) with time. For the other two samples, these magnitudes are independent of time. At low fields, the heating efficiency is higher at 5 °C than at 50 °C, whereas it shows an opposite behaviour at higher fields; the origin of this behaviour is discussed in the article. Additionally, the relaxation times,τ Nandτ B, have been calculated by considering the influence of the applied field. Chain formation requires translation and rotation of MNPs; therefore, the Brownian mechanism plays a fundamental role. It is found that magnetic reversal for 12 nm MNPs is mainly due to Néel relaxation. However, in the case of 34 nm MNPs, both mechanisms, Néel and Brownian relaxation, can be present depending on the amplitude of the field; forμ 0H< 22 mT, the physical rotation of the particle is the dominant mechanism; on the other hand, forμ 0H> 22 mT, both mechanisms are present within the size distribution. This highlights the importance of taking the field intensity into account to calculate relaxation times when analysing the relaxation mechanisms of magnetic colloids subjected to AC fields.
UR - http://www.scopus.com/inward/record.url?scp=85117296332&partnerID=8YFLogxK
U2 - 10.1039/d1na00463h
DO - 10.1039/d1na00463h
M3 - Article
VL - 3
SP - 5801
EP - 5812
JO - Nanoscale Advances
JF - Nanoscale Advances
IS - 20
ER -