Evaluation of effective magnetic anisotropy constant of magnetic nanoparticles from coercive field of AC magnetization curve

2021 ◽  
Vol 130 (18) ◽  
pp. 183901
Author(s):  
Keiji Enpuku ◽  
Sebastian Draack ◽  
Frank Ludwig ◽  
Takashi Yoshida
Keyword(s):  
Magnetic Nanoparticles ◽  
Magnetic Anisotropy ◽  
Coercive Field ◽  
Magnetization Curve ◽  
Anisotropy Constant ◽  
Magnetic Anisotropy Constant ◽  
Effective Magnetic Anisotropy ◽  
Ac Magnetization

scholarly journals Nanoparticle Size Threshold for Magnetic Agglomeration and Associated Hyperthermia Performance

Nanomaterials ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 2786
Author(s):  
David Serantes ◽  
Daniel Baldomir
Keyword(s):  
Magnetic Nanoparticles ◽  
Magnetic Anisotropy ◽  
Magnetic Dipole ◽  
Anisotropy Constant ◽  
K Value ◽  
Threshold Size ◽  
Magnetic Anisotropy Constant ◽  
Agglomeration Process ◽  
Size Threshold

The likelihood of magnetic nanoparticles to agglomerate is usually estimated through the ratio between magnetic dipole-dipole and thermal energies, thus neglecting the fact that, depending on the magnitude of the magnetic anisotropy constant (K), the particle moment may fluctuate internally and thus undermine the agglomeration process. Based on the comparison between the involved timescales, we study in this work how the threshold size for magnetic agglomeration (daggl) varies depending on the K value. Our results suggest that small variations in K-due to, e.g., shape contribution, might shift daggl by a few nm. A comparison with the usual superparamagnetism estimation is provided, as well as with the energy competition approach. In addition, based on the key role of the anisotropy in the hyperthermia performance, we also analyse the associated heating capability, as non-agglomerated particles would be of high interest for the application.

scholarly journals Температурные изменения магнитной структуры мультиферроика BiFe-=SUB=-0.80-=/SUB=-Cr-=SUB=-0.20-=/SUB=-O-=SUB=-3-=/SUB=-

2019 ◽  
Vol 61 (6) ◽  
pp. 1107
Author(s):  
В.С. Русаков ◽  
В.С. Покатилов ◽  
А.С. Сигов ◽  
А.А. Белик ◽  
М.Е. Мацнев
Keyword(s):  
Magnetic Anisotropy ◽  
Temperature Dependence ◽  
Spin Wave ◽  
Easy Axis ◽  
Anisotropy Constant ◽  
Paramagnetic State ◽  
Mössbauer Study ◽  
Magnetic Anisotropy Constant ◽  
Effective Magnetic Anisotropy ◽  
Anharmonicity Parameter

AbstractThe results of a Mössbauer study of the magnetic structure of multiferroic BiFe_0.80Cr_0.20O_3 in the temperature range of 5–550 K are presented. It is found that a collinear antiferromagnetic structure of the G type is present in BiFe_0.80Cr_0.20O_3 at temperatures below 260 K. Above 260 K, an anharmonic spin wave with a magnetic anisotropy of the easy-axis type with a high value of the anharmonicity parameter m arises. With a further increase in the temperature, the m parameter decreases and tends to zero at T ~ 420 K, at which a harmonic spin wave comes into existence. Above a temperature of about 420 K, the m parameter increases again and the spin wave becomes anharmonic with an easy-plane magnetic anisotropy. At the Néel temperature, T _N = 505 ± 10 K, the sample undergoes a transition from the magnetically ordered to the paramagnetic state. The change in the type of magnetic anisotropy at T ~ 420 K is explained by competing contributions of different signs to the effective magnetic anisotropy constant and their different temperature dependence for the BiFe_0.80Cr_0.20O_3 multiferroic.

Exchange Bias in CrO2/Cr2O3 Bilayer Thin Films

2006 ◽  
Vol 45 ◽  
pp. 2528-2533 ◽  
Author(s):  
S. Srinath ◽  
N.A. Frey ◽  
H. Srikanth ◽  
G.X. Miao ◽  
A. Gupta
Keyword(s):  
Thin Films ◽  
Magnetic Anisotropy ◽  
Variable Thickness ◽  
Exchange Bias ◽  
Exchange Coupling ◽  
Hysteresis Loops ◽  
Anisotropy Constant ◽  
Effective Magnetic Anisotropy ◽  
Large Anisotropy

We have investigated the exchange bias in CVD grown epitaxial CrO2/Cr2O3 bilayer thin films using hysteresis loops and resonant RF transverse susceptibility. M-H loops indicated an enhanced coercivity without appreciable loop shift and the transverse susceptibility in CrO2/Cr2O3 bilayers revealed features associated with both the ferromagnetic and antiferromagnetic phases. In addition, TS yielded large anisotropy constant (Keff) values depending on the fraction of Cr2O3 present. The large anisotropy fields observed cannot be accounted for by the variable thickness of CrO2 alone and are indicative of possible exchange coupling between CrO2 and Cr2O3 phases that significantly affects the effective magnetic anisotropy.

Temperature Behavior of Magnetization in Multiphase Co-P Powders in Unsaturated Regime

2015 ◽  
Vol 233-234 ◽  
pp. 522-525
Author(s):  
Oksana Anatoljevna Li ◽  
Sergey Viktorovich Komogortsev ◽  
Rauf S. Iskhakov ◽  
Lidia Aleksandrovna Chekanova ◽  
Evgeniy V. Eremin
Keyword(s):  
Magnetic Anisotropy ◽  
Temperature Dependence ◽  
Spontaneous Magnetization ◽  
Anisotropy Constant ◽  
Surprising Result ◽  
Zero Temperature ◽  
Bloch Constant ◽  
Magnetic Anisotropy Constant ◽  
Fitting Parameters ◽  
Good Agreement

In this paper we have proposed a modified expression for the fitting M(T) data in Co-P powders with nanocorundum and nanodiamond precipitates. The expression for M(T) takes into account the effects from both thermal magnetic excitations – Bloch’s T 3/2 law and temperature dependence of the magnetic anisotropy. The fitting parameters are spontaneous magnetization at absolute zero temperature, Bloch constant and order of magnetic anisotropy constant. The obtained Bloch constant is in good agreement with literature data. The order of magnetic anisotropy constant is found to be about 3 that is surprising result and supposedly comes from multiphase nature of the investigated Co-P powder.

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