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1.
The heating ability of mineral oil-based magnetic fluids with different magnetic particle concentrations is studied. The calorimetric
measurements were carried out in an alternating magnetic field of 500 A · m−1 to 2500 A · m−1 amplitude and of 1500 kHz frequency. The revealed H
n
law-type dependence of the temperature increase rate, (dT/dt)
t=0, on the amplitude of the magnetic field indicates the presence of superparamagnetic and partially ferromagnetic particles
in the tested samples since n > 2. The specific absorption rate (SAR) defined as the rate of energy absorption per unit mass increases with a decrease
of the volume fraction of the dispersed phase. This can be explained by the formation of aggregates in the samples with a
higher concentration of magnetic particles. 相似文献
2.
M. Izydorzak A. Skumiel M. Leonowicz M. Kaczmarek-Klinowska A. D. Pomogailo G. I. Dzhardimalieva 《International Journal of Thermophysics》2012,33(4):627-639
Magnetic Co-beads were fabricated in the course of a three-step procedure comprising preparation of a metal–acrylamide complex,
followed by frontal polymerization and finally pyrolysis of the polymer. The composites obtained were composed of cobalt nanocrystallites
stabilized in a carbon matrix built of disordered graphite. The crystallite size, material morphology, fraction of the magnetic
component, and thus the magnetic properties can be tailored by a proper choice of the processing variables. The samples were
subjected to an alternating magnetic field of different strengths (H = 0 to 5 kA · m−1) at a frequency of f = 500 kHz. From the calorimetric measurements, we concluded that the relaxation processes dominate in the heat generation
mechanism for the beads pyrolyzed at 773 K. For the beads pyrolyzed at 1073 K, significant values of magnetic properties,
such as the coercive force and remanence give substantial contribution to the energy losses for hysteresis. The specific absorption
coefficient (SAR) related to the cobalt mass unit for the 1073 K pyrolyzed beads (SAR = 1340 W ·g-1 cobalt){({\it SAR} = 1340 \, \, {\rm W} \cdot {\rm g}^{-1 }_{\rm cobalt})} is in very good conformity with the results obtained by other authors. The effective density power loss, caused by eddy currents,
can be neglected for heating processes applied in magnetic hyperthermia. The Co-beads can potentially be applied for hyperthermia
treatment. 相似文献
3.
S. A. Gudoshnikov B. Y. Liubimov Y. S. Sitnov V. S. Skomarovsky N. A. Usov 《Journal of Superconductivity and Novel Magnetism》2013,26(4):857-860
The electrodynamic method is applied to determine the specific absorption rate (SAR) of an assembly of superparamagnetic nanoparticles as a function of frequency and magnetic field amplitude. The home made frequency-adjustable electromagnet is used to create a nearly uniform magnetic field in a core gap of a volume 1×3×3 cm3 in the frequency range f=10–150 kHz and for magnetic field amplitudes up to H 0=250 Oe. Two oppositely connected pick-up coils are used to record the electromotive force signal (EMF) generated by magnetic nanoparticles. By integrating the EMF signal one can determine the low-frequency hysteresis loops of the assembly and the assembly SAR. Using this method the measurement of SAR has been carried out for magnetite nanoparticles with an average diameter D=25 nm. The electrodynamic method is shown to be capable of measuring a small amount of magnetic nanoparticles, up to 5×10?5 g, dispersed in a solid matrix. The maximal SAR ~?80 W/g has been obtained for the magnetite nanoparticle assembly investigated. 相似文献
4.
Alev Ayd?ner Bakiye ?ak?r Mehmet Ba?o?lu Hironori Seki Atikorn Wongsatanawarid Masato Murakami Ekrem Yanmaz 《Journal of Superconductivity and Novel Magnetism》2012,25(2):391-397
In this work, single-crystal samples 20 mm in diameter were grown by a cold top-seeding method. In order to study the effect
of an Y2O3 buffer layer, a compacted precursor was located in a crucible on a buffer layer of freely poured Y2O3 powder. The YBCO bulk samples were carefully prepared in the same chemical composition. In order to examine the homogeneity
of the samples, rectangular specimens were cut from a sample. The structural orientation of the specimens was measured by
a X-ray diffractrometer (XRD). The microstructure was observed with a Scanning Electron Microscope (SEM). The magnetic properties
were measured using a Vibrating Sample Magnetometer (VSM) at 77 K with the applied magnetic field parallel to the c-axis. As a result only (00l) peaks were observed in X-ray diffraction data, indicating that all specimens are highly oriented with the c-axis perpendicular to the top surface. Also the cut samples exhibited very fine Y211 inclusion distributed in the bulk sample
observed in SEM micrographs. The critical current density J
c (A/cm2) has been estimated by the extended Bean model. The maximum value of the critical current density at 77 K is 5.2×104 A/cm2 in a self-field. The trapped magnetic field measurements of the samples were performed by using Hall probe scanning device
with static field of 0.5 T at 77 K. The single-domain sample exhibits a trapped field of 1140 G at 77 K. 相似文献
5.
Temperature-sensitive Poly (N-isopropylacrylamide), PNIPA gels were synthesized with micron-sized iron and iron oxide (Fe3O4) particles to investigate their viability for combined hyperthermia and drug release applications. The ultimate goal is to combine hyperthermia and triggered drug release. Induction heating of the magnetic hydrogels with varying concentration of magnetic powder was conducted at a frequency of 375 kHz for magnetic field strength varying from 1.7 kA/m to 2.5 kA/m. It was observed that the maximum temperature induced in the magnetic hydrogels increased with the concentration of magnetic particles and magnetic field strength. The PNIPA gel underwent a collapse transition at 34 °C. The best combination was found for the PNIPA–Fe3O4 system, 2.5 wt.% Fe3O4 in PNIPA–Fe3O4 system took 260 s to be heated to 45 °C under a magnetic field strength of 1.7 kA/m and the specific absorption rate (SAR) was found to be 1.83. SAR of iron oxide was found to be higher than the SAR of iron. 相似文献
6.
The cylindrical Ni–lead zirconate titanate (PZT)–Ni laminated composites with various magnetostrictive–piezoelectric phase
thickness ratios were synthesized by electroless deposition. The influences of the bias magnetic field (H
dc) and the ac magnetic field frequency (f) on magnetoelectric (ME) effect are discussed. It is seen that the ME voltage coefficient depends strongly on H
dc and f. The ME voltage coefficient and electromechanical resonance frequency increase as the magnetostrictive–piezoelectric phase
thickness ratio increases. The calculated resonant frequency increases with the magnetostrictive–piezoelectric phase thickness
ratio, which agrees well with the experimental results. The maximum ME voltage coefficient of the cylindrical Ni–PZT–Ni laminated
composite is 3.256 V cm−1 Oe−1, which is much higher than that of the plate laminated composite with the same magnetostrictive–piezoelectric phase thickness
ratio. Electroless deposition is an efficient method to prepare ME laminated composites with complex structures. Proper resonant
frequency and stronger ME effect can be obtained by optimizing the structure. 相似文献
7.
Yun Zhou Jincang Zhang Zhenjie Feng Beizhan Li Li Li Yuling Su Chao Jing Shixun Cao 《Journal of Materials Science》2011,46(8):2649-2653
A new kind of nano/microscale lead-free multiferroic composite with a formal of 0.4CoFe2O4–0.6[0.948(K0.5Na0.5)NbO3–0.052LiSbO3] was prepared. The electric-field-induced dielectric (EID) and magnetization (EIM) behaviors were systemically investigated
for this 0–3-type structured multiferroic ME composite. Significant electric-field-induced effects were obtained with a high
tunability and a large EIM coefficient, which the former has a value of K = 3.35% under the low dc electric-field of 2 kV/cm and the later is in excess of 2.15 × 10−10 s/m at a low frequency of 1.0 kHz with a low magnetic bias field of 2000 Oe for this composite. It is also proved that its
EIM behavior is strongly dependent on the bias magnetic field H
Bias and the frequency of driving electric-field. The measured EIM has an excellent linear relationship with the applied ac electric-field
with amplitude varying from 7.1 to 73.6 V/cm. The electric-field-induced effects indicate that the 0–3-type particulate ME
composites not only have physical interest but also have potential practical use. 相似文献
8.
A. Skumiel M. Izydorzak M. Leonowicz A. D. Pomogailo G. I. Dzhardimalieva 《International Journal of Thermophysics》2011,32(9):1973-1985
Ferromagnetic and superparamagnetic nickel nanocrystallites, stabilized in a carbon matrix, were prepared by a three-step
procedure including formation of a Ni acrylamide complex, followed by frontal polymerization and pyrolysis of the polymer
at various temperatures. It was found that the procedure applied enables fabrication of magnetic beads containing metallic
nanocrystallites embedded in a carbon matrix. The size of the crystallites, their morphology, volume fraction, and magnetic
properties can be tailored by the pyrolysis temperature. The size of the crystallites affects their behavior in an external
magnetic field, i.e., a heating process is the most effective for a sample pyrolyzed at 873 K. The revealed H
n-type dependence of the temperature increase rate, (dT/dt)
t=0, on the amplitude of the magnetic field indicates the presence of both superparamagnetic and ferromagnetic particles in all
the samples studied since n > 2. For the superparamagnetic particles, the heating mechanism is associated with Néel relaxation. For the lower values
of the magnetic field amplitude, H < H
0, the relaxation losses dominate whereas for the opposite case, H > H
0, the magnetic hysteresis is the main source of thermal energy losses. The composites containing magnetic Ni nanocrystallites
entrapped in a carbon matrix can be potentially applied for hyperthermia treatment. 相似文献
9.
Kawashita M Domi S Saito Y Aoki M Ebisawa Y Kokubo T Saito T Takano M Araki N Hiraoka M 《Journal of materials science. Materials in medicine》2008,19(5):1897-1903
Ferrimagnetic materials can be expected to be useful as thermo seeds for hyperthermic treatment of cancer, especially where
the cancer is located in deep parts of body, as they can generate heat by magnetic hysteretic loss when they are placed in
an alternating magnetic field. Recently, it was reported that ferrimagnetic maghemite (γ-Fe2O3) microspheres 20–30 μm in diameter prepared in aqueous solution can show excellent heat generating ability. However, these
microspheres have many cracks on their surfaces. In this study, the preparation conditions for the microspheres was further
optimized in order to obtain crack-free ferrimagnetic microspheres, and the in vitro heat generation of the obtained microspheres
was measured in an agar phantom under an alternating magnetic field. Crack-free γ-Fe2O3 microspheres 20–30 μm in diameter were obtained successfully. Their saturation magnetization and coercive force were 68 emu g−1 and 198 Oe, respectively. Their heat generation under an alternating magnetic field of 300 Oe at 100 kHz was estimated to
be 42 W g−1. The microspheres showed in vitro heat generation when they were dispersed in an agar phantom and placed under an alternating
magnetic field. It is believed that these microspheres may be useful for the in situ hyperthermic treatment of cancer. 相似文献
10.
Transport Properties under Magnetic Field and J
c
(H) Peak Effect on Single-Crystal Bi-2212 Whiskers
S. Altin M. A. Aksan Y. Balci M. E. Yakinci 《Journal of Superconductivity and Novel Magnetism》2009,22(8):775-784
In this study, 50 nm–18 mm in length superconducting single-crystal Bi-2212 whiskers have been fabricated using glass-ceramic
BSCCO material. The microstructure, transport and magnetic properties were characterized by XRD, SEM-EDX, R–T, I–V and M–H analysis. Highly c-axis oriented single-crystal whiskers were produced without any grain boundaries in any crystallographic
direction. T
c and T
zero were obtained to be 94.8 K and 92.8 K, respectively, and decreased with increasing the magnetic field. Magnetic properties,
M–H curves of the whiskers, were investigated at 3 different constant temperatures up to 5 T. Symmetric hysteresis loops for
all temperature and field cases were obtained and maximum J
c
mag value was calculated to be 4.58×106 A cm−2 at 10 K for 0 T but dropped to 1.61×106 A cm−2 at 30 K for 0 T.
Transport critical current density, J
c
trans, of the whiskers in low magnetic field (between 0 and 270 Oe) and in a wide temperature region (5–75 K) was investigated.
It was obtained that initially J
c
trans increased with increasing the magnetic field but then started to decrease with further increase on the magnetic field at
all temperature values. We have investigated this problem in terms of the Bulk pinning model, the Geometrical barrier model
and the Bean–Livingston surface barrier model. We have noticed that all these models were not fitted well to our data. However,
we have modified the Bean–Livingstone model by adding a new parameter. It was found that this modified formula fitted well
to the data obtained in this work and can give successful explanations to the other results obtained by other groups. 相似文献
11.
Temperature-sensitive Poly (N-isopropylacrylamide), PNIPA gels were synthesized with micron-sized iron and iron oxide (Fe3O4) particles to investigate their viability for hyperthermia applications. Induction heating of the magnetic hydrogels with
varying concentration of magnetic powder was conducted at a frequency of 375 kHz for magnetic field strength varying from
1.7 kA/m (21 Oe) to 2.5 kA/m (31.4 Oe). It was observed that the maximum temperature induced in the magnetic hydrogels increased
with the concentration of magnetic particles and magnetic field strength. The PNIPA gel underwent a collapse transition at
34 °C. It was found that a 2.5 wt.% Fe3O4 in PNIPA composite took 260 s to be heated to 45 °C under a magnetic field strength of 1.7 kA/m, the specific absorption
rate (SAR) was found to be 1.83. SAR of iron oxide was found to be higher than the SAR of iron. 相似文献
12.
M. M. Abu-Samreh A. M. Saleh R. M.-L. Kitaneh H. F. Braun 《Journal of Superconductivity and Novel Magnetism》2008,21(1):57-63
The applicability of theoretical models for the ac susceptibility measurements of polycrystalline RuSr2GdCu2O8 superconductor has been examined within the temperature range between 8–50 K, ac magnetic field 0.5–25 G, and frequency 20–12500
Hz. In general, a reasonable qualitative agreement between theory and experiment was attained. An evident and detectable asymmetry
was observed within the Cole–Cole polar plots with a peak enhancement for both theoretical and experimental data. The modified
critical state models are found to generate much better explanation of the ac susceptibility measured data than Bean’s model.
For fields above 20 G, the results are agreed roughly with the Bean critical state model, while below 20 G, the Kim–Anderson
model is more suitable to account of the magnetic performance. The temperature and field amplitude dependencies of the flux-creep
exponent, n, were extracted from the real part of susceptibility, χ′, dependence on frequency. The flux-creep exponent was found to decrease with both temperature and ac field amplitude in
accordance to a power-law of the form: n(T,H)=n
0(H)T
−s(H). Such dependence might be an indication of a crossover to flux-creep bundles regime. 相似文献
13.
S. V. Trukhanov 《Technical Physics Letters》2011,37(4):350-353
It is established that the magnetic state of the anion-deficient La0.70Sr0.30MnO2.85 manganite represents the spin-glass state of the cluster. The magnetic field at the beginning (H < 10 kOe) leads to the fragmentation of ferromagnetic clusters, then (H > 10 kOe) leads to the transition to a ferromagnetic state of an antiferromagnetic matrix and to increase in the degree of
polarization of local spins of manganese. It is determined that the freezing temperature of magnetic moments varies as T
f
= 65 − 6H
0.21. The causes and mechanism of the magnetic phase separation are discussed. 相似文献
14.
The variation of magnetization with temperature of the Zn
x
Cu1–x
Fe2O4 system has been obtained between 300 K and the Néel temperature at a constant magnetic field of 5.57×105 A m–1 for x=0 to 0.8. The observations indicate the existence of a Yafet-Kittel (Y-K) type of magnetic ordering in the mixed ferrites. A molecular field analysis of the Y-K spin-ordering using a three-sublattice model is shown to explain the experimental data satisfactorily. For the sake of verification, Néel temperatures of Cu-Zn ferrites were also determined from Mössbauer studies. 相似文献
15.
New dielectric ceramics in the SrLa4−xSmxTi5O17 (0 ≤ x ≤ 4) composition series were prepared through a solid state mixed oxide route to investigate the effect of Sm+3 substitution for La+3 on the phase, microstructure and microwave dielectric properties. At x = 0–3, all the compositions formed single phase ceramics
within the detection limit of in-house X-ray diffraction when sintered in the temperature range 1500–1580 °C. At x = 4, a
mixture of Sm2Ti2O7 and SrTiO3 formed. The maximum Sm+3-containing single phase ceramics, SrLaSm3Ti5O17, exhibited relative permittivity (εr) = 42.6, temperature coefficient of resonant frequency (τ
f
) = −96 ppm/oC and quality factor (Q
u
f
o
) = 7332 GHz. An analysis of results presented here indicates that SrLa4−xSmxTi5O17 ceramics, exhibiting τ
f
~ 0 and εr ~ 53 could be achieved at x ~ 1.4 but at the cost of decrease in Q
u
f
o
. 相似文献
16.
Pure and Zr-substituted CaCu3(Ti1−x
Zr
x
)4O12 (x = 0, 0.01, 0.02, 0.03) ceramics were prepared by the Pechini method. X-ray powder diffraction analysis indicated the formation
of single-phase compound, and all the diffraction peaks were completely indexed by the body-centered cubic perovskite-related
structure. The effects of Zr4+ ion substituting partially Ti4+ ion on the dielectric properties were investigated in frequency range between 100 Hz and 1 GHz. The low frequency (f ≤ 105 Hz) dielectric constant decreases with Zr substitution and the high frequency (f ≥ 107 Hz) dielectric constant is unchanged. Interestingly, a low-frequency relaxation was observed at room temperature through
Zr substitution. The observed dielectric properties in Zr-substituted samples were discussed using the internal barrier layer
capacitor model. A corresponding equivalent circuit was adopted to explain the dielectric dispersion. The characteristic frequency
of low-frequency relaxation rises due to the decrease of the resistivity of grain boundary with Zr substitution, which is
likely responsible for the large low-frequency response at room temperature. 相似文献
17.
P Markondeya Raj 《Bulletin of Materials Science》1995,18(5):623-630
Three independent studies have been reported on the free energy of formation of NiWO4. Results of these measurements are analyzed by the “third-law” method, using thermal functions for NiWO4 derived from both low and high temperature heat capacity measurements. Values for the standard molar enthalpy of formation
of NiWO4 at 298·15 K obtained from “third-law” analysis are compared with direct calorimetric determinations. Only one set of free
energy measurements is found to be compatible with calorimetric enthalpies of formation. The selected value for Δf
H
m
0
(NiWO4, cr, 298·15 K) is the average of the three calorimetric measurements, using both high temperature solution and combustion
techniques, and the compatible free energy determination. A new set of evaluated data for NiWO4 is presented. 相似文献
18.
Kawashita M Sadaoka K Kokubo T Saito T Takano M Araki N Hiraoka M 《Journal of materials science. Materials in medicine》2006,17(7):605-610
Ferrimagnetic materials can be expected to be useful as thermal seeds for hyperthermic treatment of cancer, especially where
the cancer is located in deep parts of body, as they can generate heat by magnetic hysteretic loss when they are placed in
an alternating magnetic field. In this study, hollow magnetite (Fe3O4) particles were prepared using an enzymatic reaction of urease. A hollow particle was obtained by using a Pasteur pipette.
The particle was 500 μm in size and was composed of Fe3O4. Its saturation magnetization and coercive force were 57 emu⋅g−1 and 183 Oe, respectively. Its heat generation under an alternating magnetic field of 300 Oe at 100 kHz was estimated to be
45 W⋅g−1. Microspheres 30 μm in diameter were also successfully obtained by using a spray gun. 相似文献
19.
The characteristics of a magnetic sensor, based on the non-linear electromagnetic response of the weak links present in polycrystalline
BPSCCO superconductor are reported. The second harmonic response of the sensor in an alternating magnetic field at 40 kHz
and at 77 K being a strong linear function of low d.c. field is utilized for magnetic field sensing. The noise limited resolution
of the sensor is found to be 3.16 x 10−9 T/√Hz forH
a.c.= 16 G and frequency 40 kHz. The magnetic sensor has been applied for nondestructive detection of various types of flaws in
ferromagnetic plates and also for detection of small magnetic inclusions in a non-magnetic matrix. Our results suggest that
the 2f response based BPSCCO superconductive magnetometer has potential for its application in the area of non-destructive
evaluation of defects in ferromagnetic materials. 相似文献
20.
xBaTiO3 + (1 − x)Ni0.93Co0.02Cu0.05Fe2O4 (x = 0.5, 0.6, 0.7, 0.8) composites with ferroelectric–ferromagnetic characteristics were synthesized by the ceramic sintering
technique. The presence of constituent phases in the composites was confirmed by X-ray diffraction studies. The average grain
size was calculated by using a scanning electron micrograph. The dielectric characteristics were studied in the 100 kHz to
15 MHz. The dielectric constant changed higher with ferroelectric content increasing; and it was constant in this frequency
range. The relation of dielectric constant with temperature was researched at 1, 10, 100 kHz. The Curie temperature would
be higher with frequency increasing. The hysteresis behavior was studied to understand the magnetic properties such as saturation
magnetization (M
s). The composites were a typical soft magnetic character with low coercive force. Both the ferroelectric and ferromagnetic
phases preserve their basic properties in the bulk composite, thus these composites are good candidates as magnetoelectric
materials. 相似文献