阅读说明：本技术 一种基于热重变化测量磁性纳米颗粒居里温度的方法 (Method for measuring Curie temperature of magnetic nanoparticles based on thermogravimetric change ) 是由 张伟 余小刚 吴承伟 于 2020-05-26 设计创作，主要内容包括：一种基于热重变化测量磁性纳米颗粒居里温度的方法,属于磁性材料的测量领域。本发明利用热重分析仪在静磁场下测量磁性纳米颗粒的m-T曲线,并在其斜率最大处作切线,该切线与曲线平衡时反向延长线的交点即为磁性纳米颗粒的居里温度。本发明采用的是简单经济的热重分析仪测量磁性纳米颗粒的居里温度,适用于颗粒形状、尺寸、磁晶各向异性常数上都是非均一的磁性纳米颗粒样品,且测量时不需要对待测磁性纳米颗粒进行任何后处理,操作简单,易于推广,所得结果与超导量子干涉仪磁强计测量结果一致,显著降低了磁性纳米颗粒居里温度的测量成本。(A method for measuring the Curie temperature of magnetic nanoparticles based on thermogravimetric change belongs to the field of measurement of magnetic materials. The method utilizes a thermogravimetric analyzer to measure an m-T curve of the magnetic nanoparticles in a static magnetic field, a tangent is made at the position with the maximum slope, and the intersection point of the tangent and a reverse extension line when the curve is balanced is the Curie temperature of the magnetic nanoparticles. The method adopts a simple and economic thermogravimetric analyzer to measure the Curie temperature of the magnetic nanoparticles, is suitable for magnetic nanoparticle samples with non-uniform particle shapes, sizes and magnetocrystalline anisotropy constants, does not need any post-treatment on the magnetic nanoparticles to be measured during measurement, is simple to operate and easy to popularize, and has the obtained result consistent with the measurement result of a magnetometer of a superconducting quantum interferometer, thereby remarkably reducing the measurement cost of the Curie temperature of the magnetic nanoparticles.)

1. A method for measuring the Curie temperature of magnetic nanoparticles based on thermogravimetric changes is characterized by comprising the following steps of:

fully grinding magnetic nanoparticles to be tested by adopting an agate mortar to obtain a test sample;

second, zero setting

Placing the covered empty crucible on a balance of a thermogravimetric analyzer, and placing a magnet 1 right above the balance to provide a static magnetic field required for measurement; after the scale reading is stable, setting zero clearing, adjusting the scale reading to zero, and eliminating system errors;

third, measure

Adding the test sample weighed in the first step into a crucible, covering the crucible, placing the crucible on a balance, setting the temperature rise speed to be 1-5 ℃/min, introducing protective gas, starting heating, and recording and drawing an m-T curve of the tested magnetic nanoparticles; the specific steps for drawing the m-T curve are as follows:

under the action of a magnetic field, the nano particles loaded on the thermogravimetric analyzer balance are acted by the action of the magnetic field force, so that the apparent weight of the balance is smaller than the actual mass of the nano particles; the magnetization intensity of the magnetic nanoparticles is reduced along with the increase of the temperature, the acting force of the magnetic field is reduced, so that the apparent weight of the balance is gradually increased, when the temperature is increased to ensure that all the magnetic nanoparticles are converted into paramagnetism, the acting force of the magnetic field on the magnetic nanoparticles is approximately zero, the apparent weight of the balance is equal to the actual mass of the nanoparticles at the moment and does not change along with the increase of the temperature, and therefore the m-T curve of the magnetic nanoparticles is obtained;

the fourth step, data processing

And (3) solving a first derivative of the m-T curve of the sample obtained in the third step, determining the position with the maximum slope, then drawing a tangent line through the point, wherein the intersection point of the tangent line and the reverse extension line when the curve is balanced is the Curie temperature of the sample.

Technical Field

The invention belongs to the field of measurement of magnetic materials, relates to measurement of magnetic properties of magnetic nanoparticles, and particularly relates to a method for measuring Curie temperature of magnetic nanoparticles based on thermogravimetric change.

Background

The curie temperature is a secondary phase transition temperature of the magnetic material, which is a temperature at which the spontaneous magnetization of the magnetic material is reduced to zero, and is a critical temperature at which (sub) ferromagnetism is converted into paramagnetism. When the temperature is lower than the curie temperature, the magnetic material is (sub) ferromagnetic and is easily magnetized by an external magnetic field. When the temperature exceeds the curie temperature, the magnetic material is paramagnetic and is difficult to be magnetized by an external magnetic field.

The curie temperature is an important performance parameter of a magnetic material, and magnetic cores with different curie temperatures need to be selected according to different circuit requirements and working conditions. The circuit cannot work properly because once the temperature of the magnetic core exceeds its curie temperature, its permeability drops sharply, causing the electromagnetic effect of the magnetic core to fail. In addition, the Curie temperature characteristic of the magnetic material can be used as a magnetic control element to control the working state of the instrument, such as an electromagnetic protection switch, temperature control in magnetic induction thermotherapy and the like. It is clear that it is crucial to accurately measure the curie temperature of a magnetic material. The most common method for measuring the curie temperature is to measure a curve of the magnetization intensity of the magnetic material changing with the temperature in a determined external magnetic field, i.e., an M-T curve, by using a superconducting quantum interferometer magnetometer according to the characteristic that the magnetization intensity of the magnetic material decreases with the increase of the temperature, and then to draw a tangent at the maximum slope of the M-T curve, wherein the intersection point of the tangent and a temperature axis (abscissa) is the curie temperature of the magnetic material.

The superconducting quantum interferometer magnetometer is expensive in equipment price and complex in operation process, a high-temperature device is usually additionally loaded when the Curie temperature is measured through an M-T curve, the technical requirement on an operator is high, the high-temperature device is easily damaged due to improper operation, and high maintenance cost is caused. In particular, superconducting quantum interferometer magnetometers are generally difficult to use directly for measuring powder samples, and require some post-processing of the powder samples, such as pressing of the powder samples to be measured into blocks for measurement. Therefore, the use of this method for measuring the curie temperature of magnetic nanoparticle powders is limited. Chinese patent publication No. CN104568209A (application No. CN201510006987.2) discloses a magnetic material Curie temperature measurement method based on thermogravimetric change. The thermogravimetric analyzer used in the method is used for measuring the substance quality under the programmed temperature controlThe instrument of the quantity variation relation with the temperature is relatively cheap, and the instrument itself has the heating function, does not need to additionally load high-temperature devices, and is simple and convenient to operate. The method has strict requirements on samples, is mainly suitable for samples with single shape of nano particles, uniform size distribution and same magnetocrystalline anisotropy constant, and is characterized in that the method measures a change curve of the mass m of the magnetic material under a certain magnetic field along with the temperature T, namely an m-T curve through a thermogravimetric analyzer, wherein the first derivative of the curve is a derivative of the m-T curveThe temperature corresponding to the maximum value of (a) is the curie temperature of the test sample. If the shape, size and magnetocrystalline anisotropy of the magnetic nanoparticles in the sample are not uniform, the curie temperature of only a part of the nanoparticles is actually measured, and the curie temperature of the magnetic nanoparticles cannot be truly reflected.

The magnetic nanoparticles produced are generally non-uniform in shape, size, magnetocrystalline anisotropy constants and have a range of distributions, limited by process parameters and operating errors. For such samples, the present invention proposes a method for measuring curie temperature using thermogravimetric analysis. The method does not need any post-treatment on the powdery magnetic nanoparticles, can directly measure the Curie temperature of the magnetic nanoparticle powder sample, is simple and convenient to operate, easy to popularize and suitable for the magnetic nanoparticle sample with non-uniform particle shape, size and magnetocrystalline anisotropy constant.

Disclosure of Invention

The invention aims to provide a method for measuring Curie temperature of a nanoparticle sample with non-uniform particle shape, size and magnetocrystalline anisotropy constant based on thermogravimetric change. The basic principle is that the change of the magnetization intensity along with the temperature is represented by the change of the mass of the magnetic nanoparticles along with the temperature, the temperature when the magnetization intensity is reduced to be approximately zero is the Curie temperature of the magnetic nanoparticles, and the influence of the shape, the size and the magnetocrystalline anisotropy constant difference of the nanoparticles on the measured Curie point is reflected. As shown in fig. 1, under the action of a magnetic field, magnetic nanoparticles loaded on a thermogravimetric analyzer balance are subjected to the action of the magnetic field force so that the apparent weight of the balance is smaller than the actual mass of the nanoparticles. The magnetization intensity of the magnetic nanoparticles is reduced along with the increase of the temperature, the acting force of the magnetic field is reduced, so that the apparent weight of the balance is gradually increased, when the temperature is increased to enable all the magnetic nanoparticles to be converted into paramagnetism (namely Curie temperature), the acting force of the magnetic field on the magnetic nanoparticles is approximately zero, the apparent weight of the balance is equal to the actual mass of the nanoparticles at the moment and does not change along with the increase of the temperature, namely the m-T curve reaches the balance.

The technical scheme adopted by the invention is specifically as follows:

a method for measuring curie temperature of magnetic nanoparticles based on thermogravimetric changes, comprising the steps of:

first, a test sample is prepared

Fully grinding the magnetic nanoparticles to be measured by adopting an agate mortar, and then weighing 10-30mg of fine and loose magnetic nanoparticle powder samples for subsequent measurement;

second, zero setting

The capped empty crucible 2 was placed on a balance 4 of a thermogravimetric analyzer, and a magnet 1 was placed directly above the balance 4 to provide a static magnetic field required for measurement. After the reading of the balance 4 is stable, setting zero clearing, and adjusting the reading of the balance to zero to eliminate the system error as much as possible;

third, measure

And (3) adding the sample weighed in the first step into a crucible 2, covering the crucible, placing the crucible on a balance 4, setting the temperature rise speed to be 1-5 ℃/min, introducing protective gas, starting heating, and recording and drawing an m-T curve of the test sample. It should be noted that the temperature rise rate cannot be too fast, otherwise the temperature would exceed the curie temperature of the sample before the system enters a steady state, so that the measurement result is greatly deviated.

The fourth step, data processing

And (3) solving a first derivative of the m-T curve of the sample obtained in the third step, determining the position with the maximum slope, then drawing a tangent line through the point, wherein the intersection point of the tangent line and the reverse extension line when the curve is balanced is the Curie temperature of the sample.

Furthermore, the protective gas introduced in the third step is nitrogen, argon, helium and the like, so as to avoid further oxidation of the sample in the heating process.

The invention has the beneficial effects that: the invention mainly aims to measure the Curie temperature of a magnetic nanoparticle powder sample, adopts a simple and economic thermogravimetric analyzer, has simple measuring method and convenient operation, and can obviously reduce the measuring cost of the Curie temperature of the magnetic nanoparticle powder sample, and the obtained result is consistent with the measuring result of a magnetometer of a superconducting quantum interferometer.

Drawings

FIG. 1 is a schematic view of a measuring device according to the present invention;

the m-T curve of the sample of FIG. 2;

fig. 3-5 show curie temperatures of the same magnetic nanoparticles measured using three methods: FIG. 3 is a superconducting quantum interferometer magnetometer; FIG. 4 is a process of the present invention; FIG. 5 shows a method disclosed in Chinese patent application No. CN 104568209A.

In the figure: 1, a magnet; 2, a crucible; 3, a computer; 4 balance.

Detailed Description

In the following, a detailed description of an embodiment of the invention will be given in conjunction with the technical implementation and fig. 4 of the accompanying description.

A method for measuring curie temperature of magnetic nanoparticles based on thermogravimetric changes, comprising the steps of:

(1) test sample preparation: prepared Zn_0.54Co_0.46Cr_0.6Fe_1.4O₄Fully grinding the magnetic nano particles, and then weighing about 10mg of fine and loose sample for later use;

(2) zero setting: the covered empty crucible 2 was placed on a balance 4, and then a 100 x 50 x 10mm crucible was placed directly above the balance 4³The magnet 1 and the balance 4 are connected with a computer 3, as shown in figure 1; to-be-measured balance stable displayResetting after setting;

(3) measurement: taking out the crucible 2 from the balance 4, adding the weighed sample into the crucible 2, covering the crucible cover, placing the crucible on the balance 4, setting the heating rate to be 5 ℃/min, introducing argon as protective gas, starting heating, and recording an m-T curve, wherein the m-T curve is shown in figure 2;

(4) data processing: a first derivative is obtained from the measured m-T curve, the position with the maximum slope is determined, then a tangent is drawn through the point, and the intersection point of the tangent and the reverse extension line when the m-T curve is balanced is the Curie temperature of the sample, as shown in FIG. 4.

The method for measuring the Curie temperature is essentially the same as the method for measuring the Curie temperature by the superconducting quantum interferometer magnetometer, and numerical results are consistent. As shown in fig. 3-5, fig. 3 shows curie temperature (external magnetic field strength is 50Oe, and testing temperature range is 5-400K) of magnetic nanoparticle sample measured by superconducting quantum interferometer magnetometer, which is a conventional curie temperature measuring method; FIG. 4 is a plot of Curie temperature of samples measured by the method of the present invention; FIG. 5 is a Curie temperature of a sample measured by the method disclosed in Chinese patent publication No. CN 104568209A. The samples measured by the three methods are the same magnetic nano powder. As can be seen from fig. 3 to 5, the difference between the curie temperature measured by the method disclosed in chinese patent publication No. CN104568209A and the curie temperature measured by the conventional measurement method (superconducting quantum interferometer magnetometer) is 33.8%, while the difference between the curie temperature measured by the present invention and the result measured by the conventional measurement method is only 0.9%, the measurement result is accurate and reliable, and the operation method is simpler and more convenient than the conventional method.

The above-mentioned embodiments only express the embodiments of the present invention, but not should be understood as the limitation of the scope of the invention patent, it should be noted that, for those skilled in the art, many variations and modifications can be made without departing from the concept of the present invention, and these all fall into the protection scope of the present invention.