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We present a new method for measuring the temperature of magnetic nanoparticles that can also be adapted to immobilized particles. The Néel relaxation mechanism, which dominates the dynamic magnetization process of immobilized magnetic nanoparticles, can be used as an intermediate parameter in a sensing model to obtain temperature information. In this paper, we use the nonlinear response properties of magnetic nanoparticles to derive an analytical expression for the relationship between the phase of cubic susceptibility and temperature. We also consider dipole-dipole interactions and the dependence on field amplitude. Under experimental conditions at selected frequencies and field amplitudes, we compare temperature measurements of magnetic nanoparticles obtained with the proposed thermometry model with those obtained from existing nonlinear dielectric relaxation models. The results show that the temperature measurements obtained from the proposed model are closer to the reference temperatures in the temperature range of 308-353 K, with a standard deviation of less than 0.1 K in the temperature measurement. This new method successfully applies the nonlinear properties of magnetic nanoparticles to high-precision dynamic temperature measurements. It extends the applicability range of temperature measurement methods to conditions with strong interactions or large ac field amplitudes. This new method is expected to be applicable in anti-magnetic environments, for example, in biochemical temperature measurements of magnetically labeled cells in vivo. [ABSTRACT FROM AUTHOR]

The precise measurement of temperature information is of great importance in the thermal management of light-emitting diodes (LEDs). Hitherto, many methods have been proposed to measure the LED temperature, but none of them involve with magnetics. Herein, we developed a noninvasive and precise method to probe the LED temperatures based on magnetic nanoparticles (MNPs). Detailed measurement principle and experimental setup were introduced. Through this setup, the heating and cooling characteristics of LEDs were investigated with different voltage inputs. It is found that higher voltage input leads to higher LED temperature. When the input voltage is 5.2 V, the LED temperature is 326.8 K. The present noninvasive and precise method supplements the existing techniques of temperature measurement in terms of magnetics and opens up new avenues to measure the temperature information where conventional approaches may fail. [ABSTRACT FROM AUTHOR]

This paper is focused on the signature of thermal-assisted cluster disruption while analyzing the inverse alternating current (AC) susceptibility (1/χ) versus temperature (T) curves recorded at lower AC frequencies (f), below 300 Hz. A commercial oil-based magnetic fluid (MF) sample was used in the experiments to investigate the critical temperature (T*) that characterizes the thermal disruption of aggregates suspended within the MF sample. T* was found to reduce as f increased within the frequency range of our investigation (63-263 Hz). Furthermore, T* was found to scale with the square of the applied AC frequency. Both theoretical and experimental evidences support that the excitation field frequency (f) dependence of the critical temperature (T*) is well described by T*(f) = T*(0)-Af2/1+Bf2. The model is based on energy absorption of magnetic nanoparticles in an AC magnetic field. [ABSTRACT FROM AUTHOR]

Instantaneous and noninvasive temperature measurements are important when laser thermotherapy or welding is performed. A noninvasive nanosecond-resolved magnetic nanoparticle (MNP) temperature measurement system is described in which a transient change in temperature causes an instantaneous change in the magnetic susceptibilities of the MNPs. These transient changes in the magnetic susceptibilities are rapidly recorded using a wideband magnetic measurement system with an upper frequency limit of 0.5 GHz. The Langevin function (the thermodynamic model characterizing the MNP magnetization process) is used to obtain the temperature information. Experiments showed that the MNP DC magnetization temperature-measurement system can detect a 14.4 ns laser pulse at least. This method of measuring temperature is likely to be useful for acquiring the internal temperatures of materials irradiated with lasers, as well as in other areas of research. [ABSTRACT FROM AUTHOR]

In this study, we propose and demonstrate the usefulness of employing time-varying magnetization of a magnetic nanoparticle (MNP) based sample, induced by low frequency (f=25 Hz) triangular-wave magnetic field, to achieve the approach of real-time recording of magnetization curve, which allows precise and noninvasive temperature probing with real-time performance. Moreover, the present report introduces the design and performed the test of a detection system for accurate and real-time recording of the magnetization curve of MNP-based samples. We found that by employing the magnetization curve of a magnetic fluid sample containing magnetite nanoparticles of about 30 nm in diameter the accuracy of the temperature probing is about 0.32 K (0.1% relative accuracy), with response time of 1 s. Furthermore, an increase in response time from 1 to 8 s improves the accuracy of temperature probing from 0.32 to 0.20 K. Finally, we envisage that breakthroughs in clinical hyper-thermia, targeted drug delivery and basic cell research can be accomplished while using the approach reported in this study. [ABSTRACT FROM AUTHOR]