Summary of doctoral thesis in material science: Study of Magnetic Induction Heating mechanisms of spinel ferrite nanoparticles M1-xZnxFe2O4 (M=Mn, Co)

Research targets of the thesis: Fabricating spinel ferrite nanoparticle M1-xZnxFe2O4 (M = Mn, Co; 0,0 ≤x≤0,7) with controlled parameters affecting to Hc , TC and D. Establishing semi-experimental models based on experimental results to explain the correlation between SLP and (Keff, D) in order to figure out suitable mechanisms for calculating SLP value of CoFe2O4 nanoparticle.

MINISTRY OF

EDUCATION AND TRAINING

VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY

GRADATE UNIVERSIY OF SCIENCE AND TECHNOLOGY



Pham Hong Nam

STUDY OF MAGNETIC INDUCTION HEATING MECHANISMS

OF SPINEL FERRITE NANOPARTICLES

This thesis was done at:

Laboratory of Biomedical Nanomaterials, Institute of Materials and Sciene, Vietnam Academy of Science and Technology

Supervisor: Assoc.Prof., Dr Do Hung Manh Assoc.Prof., Dr Pham Thanh Phong

INTRODUCTION

Currently, application of nanoparticle in magnetic hyperthermia has been increasingly researched and developed, espescially mechanisms relating heat induced process of nanoparticles Studies mainly use Linear Respones Theory (LRT) to calculate Specific Loss Power (SLP) However, this theory is not always suitable in Magnetic Induction Heating (MIH) Accordingly, application of Stoner-Wohlfarth (SW) model is necessary The first study of Hert related to thermal mechanism magnetic particles being distinguised between hysteresis loss and relaxation loss However, this distinction was not enough to establish a full theoretical model for accurate calculation of SLP A recent study demonstrated the effet of hysteresis to heat induction by using numerical simulation Although the obtained results were suitable the authors have not established a full theoretical model for solving the SLP issue Some reports showed that physical factors such as size, shape, and content

effect on the SLP value In which, the effective anisotropy constant (K eff ) and size (D)

of magnetic particle play the most important effect.Carrery et.al demonstrated that materials with different K eff s are consistent with theory models depending on the K eff

value Materials with high K eff is consistent with the LRT model In constrast, materials with low K eff is consistent with the SW model Based on these theory models, the optimal SLP value is calculated by determining the

optimal values of K eff and D These values depend on characteristics of nanoparticle including content, synthesis condition and material structure Therefore, how to select theoretical model for calculating SLP of materials is very interesting

In Vietnam, magnetic nanopartices for biomedical application are concerned

by a number of research groups at Institute of Materials Science (IMS), Institute for Tropical Technology (ITT), Hanoi University of Science and Technology (HUST) However, only research group at IMS studies deeply about physical mechanisms relating to hyperthermia The research group not only focuses on fabircation of spinel ferrite nanoparticles (Fe3O4, MnFe2O4, CoFe2O4), manganite nanoparticles (LSMO), alloy nanoparticles (CoPt, FeCo) but also figures out physical mechanisms through experimental results and theoretical calculation However, contribution of each physical mechanism in nanoparticles is not fully calculated

Fe3O4 magnetic nanoparticle is alway the best selection for in-vitro and in-vivo

magnetic hyperthermia thanks to easy fabrication and excellent biocompatibility

However, the Curie temperature (T C) of Fe3O4 (T C = 823K) is much higher than the required temperature for killing cancer cell Thus, the saturation heating temperature

is controlled by changing nanoparticle concentration and magnetic fied intensity Recently, magnetic nanoparticles with suitable Curie temperature (TC = 42 - 46oC), high saturation magnetisation and good biocompatibility have been focusing The spinel- structured nanomaterial M1-xZnxFe2O4 (M= Mn, Co; 0,0 ≤x≤0.7) is high potential because of good ability in controlling TC (or saturation heating temperature)

In addition, CoFe2O4 nanoparticle have attracted a great deal of attention thanks to high anisotropy constant Therefore, this material has high SLP value

Based on the above reasons, we chose the research project for thesis, namely:

Study of Magnetic Induction Heating mechanisms of spinel ferrite nanoparticles

M 1-x Zn x Fe 2 O 4 (M=Mn, Co)

Research object of the thesis:

Spinel ferrite nanoparticle M1-xZnxFe2O4 (M = Mn, Co; 0,0 ≤ x ≤ 0,7)

Research targets of the thesis:

Fabricating spinel ferrite nanoparticle M1-xZnxFe2O4 (M = Mn, Co; 0,0 ≤x≤0,7)

with controlled parameters affecting to H c , T C and D

Establishing semi-experimental models based on experimental results to

explain the correlation between SLP and (K eff , D) in order to figure out suitable

mechanisms for calculating SLP value of CoFe2O4 nanoparticle

Scientific and practical meaning of the thesis:

Applying 2 theoritical models (LRT and SW) to figure out physical mechanisms contributing to the formation of SLP which helps to more clearly understand about MIH in order to apply magnetic nanoparticle

Research methodology:

The thesis was carried out by practical experimental combining with numerical data process Random samples were fabricated by hydrothermal and thermal decomposition synthesis Samples were characterized by electron microscopes (FESEM and TEM) Magnetic properties of material were investigated by Vibrating-Sample Magnetometer (VSM), PPSM, SQUID FTIR, TGA were used to evaluate the

presence of functional groups on magnetic nanoparticles DLS was used to determind the hydrodynamic diameter and stability of magnetic fluid Magnetic Induction Heating was carried out on 2 equipments: RDO-HFI- 5 kW and UHF-20A- 20 kW

Research contents of the thesis:

Investigating the effect of fabrication parameters (reaction time, temperature,

Zn content) on structure and magnetic properties of M1-xZnxFe2O4 nanoparticles (M =

Evaluating toxicity of magnetic fluid for hyperthermia testing on cancer cells

Layout of the thesis:

The contents of thesis were presented in 5 chapters Chapter 1 is review of spinel ferrite materials Chapter 2 is about physical mechanisms and theoretical models applying in magnetic induction heating (MIH) Chapter 3 presents experimental methods for fabricating nanoparticles Chapter 4 is the results of fabrication of M1-xZnxFe2O4 (M=Mn, Co; 0,0 ≤ x ≤ 0,7) obtained by hydrothermal method Chapter 5 is the results of fabrication of CoFe2O4 obtained by thermal decomposition method

Research results of the thesis were published in 07 scientific reports including:

02 ISI reports, 03 national reports, 02 reports in national and international scientific workshop

Main results of the thesis:

Investigated effect of fabrication paramters on structure and magnetic properties of M1-xZnxFe2O4 (M=Mn, Co; 0,0 ≤ x ≤ 0,7)

Fabricated CoFe2O4 nanoparticles with different size The effect of size on magnetic properties and SLP values was studied Applying numerical data process to find out the optimal size for magnetic induction heating Using critical parameters of LRT and SW models evaluate the mechanism contributing to formation of SLP

Evaluated toxicity of magnetic fluid, carried hyperthermia experiment on cancer cell (Sarcoma 180)

Chapter 1 REVIEW OF SPINEL FERRITE MATERIALS

1.1 Structure and magnetic properties of spinel ferrite materials

1.1.1 Structure of spinel ferrite materials

Ferrite spinel is term of materials which have structure containing 2 crystal lattices The interaction between 2 crystal lacttices is ferromagnetic interaction An unit cell of spinel ferrite crytal ( lattice constant – a ≈ 8,4 nm) is formed by 32 O2-atoms and 24 cations (Fe2+, Zn2+, Co2+, Mn2+, Ni2+, Mg2+, Fe3+ and Gd3+) There are 96 positions for cations (64 octa-positions, 32 tetra-positions)

1.1.2 Magnetic property of spinel ferrite materials

Based on molecular field theory, the origin of magnetic property of spinel ferrite material is the result of indirect interaction between metal ions (magnetic ions) locating in two lattices A and B through oxygen ions

1.2 Effecting factors on magnetic property of spinel ferrite nanoparticles

Magnetic property of spinel ferrite nanoparticls is determined by factors including size, shape and content

1.3 Dynamic state of magnetic nanoparticles

1.3.1 Non-interacting magnetic nanoparticles

Based on classical theory, spin- reversed speed of particle through potential energy depends on thermal energy and frequency according to Arrehenius law,

calculating equation of relaxation time (τ 0 ~ 10-9 - 10-13 s) for non-interacting

magnetic nanoparticles

1.3.2 Weakly interacting magnetic nanoparticles

Shtrikmann and Wohlfarth used mean field theory to establish the expression

of releaxtion time of weaky interacting magnetic nanoparticles under Vogel-Fulcher

law

1.3.3 Strong interacting magnetic nanoparticles

By measuring the change of phase transition temperature by frequency in a wide range, the state of material could be determined whether spin glass or not when processing data by critical slowing down model

1.4 Biomedical application of magnetic nanoparticle

Magnetic nanoparticle has been studying for 4 medical applications including cell separation, drug delivery, MRI and magnetic hyperthermia

Chapter 2 PHYSICAL MECHANISMS AND THEORETICAL MODELS

APPLIED IN MAGNETIC INDUCTION HEATING (MIH)

2.1 Induction heating mechanism of magnetic nanoparticls under AC magneitic field

2.1.1 Relaxation mechanism (Néel and Brown)

In case of single domain size, anisotropic energy is smaller than heat energy, spin of nanoparticle could rotate every direction even without magnetic field If roating spin while keeping particle in one direction then after a period of time, spin will return to the original position That is Néel relaxtion time

Néel relaxation is rotation of moment of magnetic nanoparticle Brown relaxation is the movement of magnetic nanoparticls in liquid

2.1.2 Hysteresis loss mechanism

Hysteresis loss is energy loss in a magnetism process, determined by the area

of hysteresis loop of material This process strongly depends on magnetic field

intensity and intrinsic property of mangnetic nanoparticle

2.1.3 Other mechanisms

Beside 2 above mechanisms, induction heating of magnetic nanoparticle induces heat under AC magnetic field also happens by another mechanism That is the loss induced by friction in liquid

2.2 Theoretical models

2.2.1 Stoner-Wohlfarth (SW) model

The SW model is a theoretical model use calculating the area energy of the delay of material when it magnetized to saturated LRT model is not suitable for materials without supperparamagnetism Accordingly, SW model is used Theoretically, some authors calculated magnetic resistance force by following equation:

2.3 Calculation methods of Specific Loss Power (SLP)

a) Heat measurement method

This is the most common method for determining heat induction capacity of magnetic liquid SPL value is calculated by the rate of increasing temperature:

(2.24)

b) Hysteresis loop measurement method

SLP is calculated from hysteresis loop corresponding to applied magnetic field:

∮ (2.27)

2.4 State of art of Magnetic Heat Induction study

Studies of MHI used many materials such as single nanoparticle, coupled materials, core-shell materials Supperparamagnetic nanoparticles, Fe3O4 and γ-Fe2O3, are most common studied thanks to good biocompatibility, specially success

exchange-in MRI apllication

Chapter 3 EXPERIMENTAL METHODS 3.1 Fabrication of M 1-x Zn x Fe 2 O 4 (M = Mn, Co; 0,0 ≤ x ≤ 0,7) nanoparticle by hydrothermal method

M1-xZnxFe2O4 (M = Mn, Co; 0,0 ≤ x ≤ 0,7) nanoparticles were fabricated by hydrothermal method described in the following diagram (Figure 3.1.)

Figure 3.1 Fabrication process of M 1-x Zn x Fe 2 O 4 (M = Mn, Co; 0,0 ≤ x ≤ 0,7)

Figure 3.2 Fabrication process of

CoFe 2 O 4 @OA/OLA nanoparticles

Figure 3.2 PMAO encaosulation

process

3.2.3 Phase transition of magnetic nanoparticle from organic solvent to water

Phase transition process of magnetic nanoparticle from organic solvent to water was performed in the following diagram (Figure 3.5.)

3.3 Characterization methods

Samples were characterized by electron microscopes (FESEM and TEM) Magnetic properties of material were investigated by Vibrating-Sample Magnetometer (VSM), PPSM, SQUID FTIR, TGA were used to evaluate the presence of functional groups on magnetic nanoparticles DLS was used to determind the hydrodynamic diameter and stability of magnetic fluid Magnetic Induction Heating was carried out

on 2 equipments: RDO-HFI- 5 kW and UHF-20A- 20 kMaterial structure was studied

by X-ray diffraction, electron microscopy

3.4 Toxicity evaluation of magnetic fluid on cancer cell

Evaluating cancer cell killing ability of magnetic fluid on cancer cell

3.5 Magnetic hyperthermia of magnetic fluid on cancer cell

Evaluating death ratio of cancer cell after magnetic hyperthermia by changing temperature and magnetic fied application time

Chapter 4 STRUCTURE, MAGNETIC PROPERTY AND MAGNETIC INDUCTION HEATING OF M 1-x Zn x Fe 2 O 4 (M = Mn, Co; 0,0 ≤ x ≤ 0,7)

NANOPARTICLES FABRICATED BY HYDROTHERMAL METHOD

4.1 Effect of reaction temperature on structure and magnetic property

4.1.1 Effect of reaction temperature on structure

Figure 4.1 X-ray diffraction of samples: MnFe 2 O 4 (a) and CoFe 2 O 4 (b) at different

temperatures in 12 hours

Figure 4.1a and 4.1b are the X-ray diffraction of MnFe2O4 and CoFe2O4

nanoparticles fabricated by hydrothermal method at different temperatures, coded:

120oC (MnFe1, CoFe1), 140oC (MnFe2, CoFe2), 160oC (MnFe3, CoFe3) and 180oC (MnFe4, CoFe4) with reaction time of 12 hours It was showed that both kinds of sample are single crystal expressed at characteristic peaks (220), (311), (222), (440), (442), (511), (440) When increasing temperature reaction, particle size of two kinds

of sample increases

4.1.2 Effect of reaction temperature on magnetic property

Saturation magnetism M s increases from 31,1 emu/g (MnZn1) to 66,7 emu/g (MnZn4) (Figure 4.4a) and from 59,3 emu/g (CoZn1) to 68,8 emu/g (CoZn4) when changing reaction temperature from 120oC to 180oC (Figure 4.4b)

MnFe4

MnFe3 MnFe2

Figure 4.4 Hysteresis loop of MnFe 2 O 4 (a) và CoFe 2 O 4 (b) nanoparticles fabricated

at different temperature Smaller figures are hysteresis loops at low magnetic field

4.2 Effect of reaction time on structure and magnetic property

4.2.1 Effect of reaction time on structure

Changing reaction time: 6h, 8h, 10h, 12h at reaction temperature 180oC for fabrication of MnFe2O4 và CoFe2O4 nanoparticles coded: (MnFe7, CoFe7); (MnFe6, CoFe6); (MnFe5, CoFe5) và (MnFe4, CoFe4), all sample are single crystal with ferrite spinel structure Reaction time increasing led to increasing diffraction peak intensity, decreasing peak wide which determine the decrease of particle size

4.2.2 Effect of reaction time on magnetic property

Figure 4.8 Hysteresis loops of MnFe 2 O 4 (a) and CoFe 2 O 4 (b) fabricated at different

reaction times Smaller figures are hysteresis loops at low magnetic field

Figure 4.8 are hysteresis loops of MnFe2O4 and CoFe2O4 nanoparticles measured under mangetic field from -11 kOe to 11 kOe In both kinds of sample,

decreasing reaction time from 12h to 6h led to reduction of M s Magnetic resistance

CoFe4 CoFe2

CoFe4

CoFe5 CoFe6

CoFe4 CoFe6

force H c for both kinds of samples changed but it did not follow the law of Herzer

which is that H c decreases when particle size decreases only in single domain size

range

4.3 Effect of Zn 2+ content on structure and magnetic property

4.3.1 Effect of Zn 2+ content on structure

With the aim of fabricating materials possessing Curie temperature lower than

42oC-46oC (temperature kills cancer cell), we studied effect of Zn2+ on structure and magnetic property of Mn1-xZnxFe2O4 và Co1-xZnxFe2O4 (x = 0,0; 0,1; 0,3; 0,5 và 0,7) nanoparticles, coded: MnZn0, MnZn1, MnZn3, MnZn5 và MnZn7; CoZn0, CoZn1, CoZn3, CoZn5 và CoZn7 All samples were fabricated at 180oC in 12h X-ray diffraction in figure 4.9 show that both kinds of sample are single phase spinel structure However, diffraction peaks of Mn1-xZnxFe2O4 are sharper than that of Co1-

xZnxFe2O4, meaning that the size of Mn1-xZnxFe2O4 nanoparticle is bigger than that of

Co1-xZnxFe2O4 nanoparticle In one kind of sample, increasing Zn2+ leads to decreasing intensity of diffraction peaks showing that the particle size decreases

Figure 4.9 X-ray diffractions of Mn 1-x Zn x Fe 2 O 4 nanoparticles (x = 0,0; 0,1; 0,3; 0,5 and 0,7) (a) and Co 1-x Zn x Fe 2 O 4 nanoparticles (x = 0,0; 0,1; 0,3; 0,5 và 0,7) (b)

4.3.2 Effect of Zn 2+ content on magnetic property

Figure 4.14 shows hysteresis loops of Mn1-xZnxFe2O4 nanoparticles (x = 0,0; 0,1; 0,3; 0,5 và 0,7) measured at room temperature Compared to MnZn0 sample

without Zn, M s achieved the highest values at 66,7 emu/g and gradualy decreased

when increased Zn2+ content MnZn7 sample had the lowest value at 29,8 emu/g Temperature dependence of magnetism of samples measured at 100 Oe, in Field Cooled manner was showed in figure 4.15 Samples exhibited the ferromagnetic-

CoZn3 CoZn5

CoZn7

(b)

paramagnetic phase transition at differrent T C T C values of MnZn0, MnZn1, MnZn3, MnZn5 và MnZn7 were 620 K, 560 K, 440 K, 350 K và 330 K

Figure 4.14 Hysteresis loops of

Mn 1-x Zn x Fe 2 O 4 (x = 0,0; 0,1; 0,3; 0,5

and 0,7) Smaller figure is hysteresis

loop at low magnetic field

Figure 4.15 Temperature dependence of magnetism of

Mn 1-x Zn x Fe 2 O 4 (x = 0,0; 0,1; 0,3; 0,5 and 0,7) measured at 100 Oe.

For Co1-xZnxFe2O4 nanoparticles (x = 0,0; 0,1; 0,3; 0,5 and 0,7), the change of

M s was similar to Mn1-xZnxFe2O4 nanoparticles M s decreased when increasing Zn2+content, achieving the highest value at 68,8 emu/g at x = 0,0 The reduction of saturation magnetism of Co1-xZnxFe2O4 nanoparticels could be explained by core-shell structure In this structure, the core has magnetism, shell is considered as non-magnetism because of that spin on the surface of shell arrange disorderly Temperature dependence of magnetism of Co1-xZnxFe2O4 (x = 0,0; 0,1; 0,3; 0,5 and 0,7) measured in FC and ZFC (Zero Field Cooled - ZFC) manners at 100 Oe was

showed in figure 4.17 From the results, T C and Blocking temperaute (T B) were

determined Below T B , randomly orriented spins are “locked” at non-stable state

This state is gradually lost when temperature increase to T B Under magnetic field, spins are oriented in the direction of magnetic field Thus, magnetism value measured

in FC manner is higher than that in ZFC manner and little changes at T < T B

MnZn0

MnZn3 MnZn5 MnZn7

0 2 4 6 8

MnZn0 MnZn1 MnZn3 MnZn5 MnZn7