34 results about "Magnetic transition temperature" patented technology

A magnetocaloric effect heterostructure having a core layer of a magnetostructural material with a giant magnetocaloric effect having a magnetic transition temperature equal to or greater than 150 K, and a constricting material layer coated on at least one surface of the magnetocaloric material core layer. The constricting material layer may enhance the magnetocaloric effect by restriction of volume changes of the core layer during application of a magnetic field to the heterostructure. A magnetocaloric effect heterostructure powder comprising a plurality of core particles of a magnetostructural material with a giant magnetocaloric effect having a magnetic transition temperature equal to or greater than 150 K, wherein each of the core particles is encapsulated within a coating of a constricting material is also disclosed. A method for enhancing the magnetocaloric effect within a giant magnetocaloric material including the step of coating a surface of the magnetocaloric material with a constricting material is disclosed.

PCT No. PCT/JP96/02665 Sec. 371 Date Sep. 11, 1998 Sec. 102(e) Date Sep. 11, 1998 PCT Filed Sep. 17, 1996 PCT Pub. No. WO97/11578 PCT Pub. Date Mar. 27, 1997The present invention relates to a temperature controller used for an electromagnetic induction heating apparatus provided with a heating element made of magnetic material, and prepared in a fluid passage. A coil is prepared in the perimeter of the heating element and a high frequency electric current generator for the coil. The temperature controller comprises an electric current detection unit measuring the electric current flowing from the high frequency electric current generator to the coil and detecting that the temperature of magnetic material forming the heating element reaches in the vicinity of the magnetic transformation temperature, and an electric current restrictive unit limiting the electric current flowing to the coil based on the electric current detection unit. When the temperature of the heating element reaches in the vicinity of the magnetic transformation temperature, the electric current detection unit detects the rising electric current and the electric current restrictive unit limits the further rising electric current.

The invention discloses a temperature measurement method based on trivalent rare earth ferrous oxides as temperature sensing materials, and belongs to the technical field of thermally responsive materials. The trivalent rare earth ferrous oxides are prepared through a pressureless sintering technology by using trivalent rare earth oxides and ferric oxides as the raw materials. Under the excitation of THz waves, the trivalent rare earth ferrous oxides can radiate out narrow band THz waves, and the center frequency of the narrow band THz waves obviously change along with temperature, so the trivalent rare earth ferrous oxides can be used as the temperature sensing materials and applied to temperature measurement. In the temperature measuring process, a circuit does not need to be led in, and the measurement effect can be good at low temperature. The working temperature range of the temperature sensing materials is wider, theoretically, 0K to antiferromagnetic-paramagnetic transition temperature (650-750K) can be achieved, and the working mode can be in a transmission type or a reflection type. In addition, due to the fact that the THz waves have a good permeance property to most of materials except for metal and strong polar materials, the THz waves can be used for measuring the internal temperature of a closed space.

Multiferroic articles including highly resistive, strongly ferromagnetic strained thin films of BiFe_0.5Mn_0.5O₃ (“BFMO”) on (001) strontium titanate and Nb-doped strontium titanate substrates were prepared. The films were tetragonal with high epitaxial quality and phase purity. The magnetic moment and coercivity values at room temperature were 90 emu/cc (H=3 kOe) and 274 Oe, respectively. The magnetic transition temperature was strongly enhanced up to approximately 600 K, which is approximately 500 K higher than for pure bulk BiMnO₃.

A big magnetic entropy variation compound and its preparing method are disclosed. It consists of NixMnyGaz (50 is less than or equal to x is less than or equal to 56, 22 is less than or equal to y is less than or equal to 30, 22 is less than or equal to z is less than or equal to 30), with martensite and magnetic conversion under -80deg.C- 80deg.C. When 53 is less than or equal to x is less than or equal to 56, 19 is less than or equal to y is less than or equal to 22, 23 is less than or equal to z is less than or equal to 26, it make austenite phase-transition temperature range and magnetic transition temperature between -20deg.C-80 deg.C by component regulation. It is prepared by proportioning nickel, mangan and gallium etc. raw materials by chemical component, laying vacuum arc furnace or inducing furnace, vacuum pumping up to 10 to the power -1 , passing argon, smelting and cooling to obtain uniform compound, homogeneous treating the compound for 24-120 hrs under 900-1100deg.C, and annealing for 12-72 hrs under 600-800deg.C. Its advantages include simple process, big magnetic entropy and regulating temperature.

The invention relates to an Er-based amorphous low-temperature magnetic refrigeration material and a preparation method thereof. The Er-based amorphous low-temperature magnetic refrigeration material has a general chemical formula: EraTbAlc, wherein T is one of Fe, Co, Ni or Cu; a ranges from 56 to 63, b ranges from 18 to 33, c ranges from 16 to 28, and a plus b plus c is equal to 100. The method comprises the steps of (1) preparing materials, wherein Er is slightly excessive; (2) carrying out electric arc melting until completely melting under an inert gas condition, naturally cooling after heat preservation, and repetitively melting to obtain an alloy ingot with homogeneous compositions; (3) after cleaning a surface, crushing into small blocks of alloy ingots; and (4) adopting an induction melting melt-spinning device for completely melting the ingots under an inert gas condition, carrying out melt-spinning after heat preservation, and obtaining the Er-based amorphous low-temperature magnetic refrigeration material. The material provided by the invention has the width ranging from 2 to 2.8mm and the thickness ranging from 35 to 42mm; under 0 to 7T magnetic variation, the magnetic transition temperature ranges from 8 to 18K, the maximal magnetic entropy ranges from 12.6 to 22.5J/kgK, and the magnetic refrigerant capacity ranges from 480 to 620J/kg; and the glass transition temperature ranges from 550 to 640K, the crystallization temperature ranges from 640 to 700K, and the cold liquid phase region width ranges from 33 to 65K.

Present invention refers to method determining sparse magnetic semiconductor gallium manganese arsenium ferromagnetic transition thermometric through measuring transport property. It features 1, etching gallium manganese sample to Hall element shape, making electrode adopting indium pressure welding technology, said electrode connected with constant current source and voltmeter, 2, putting Hall element in closed loop refrigeration system, 3, measuring Hall element tangential grinder resistance with thermometric relation curve, determining gallium manganese arsenium conduct characteristic, phase transition temperature from insulativity converting to metallicity, thereby determining gallium manganese arsenium thin-film ferromagnetic transition temperature.

The invention discloses a Gd-based amorphous nanocrystal composite with high Curie temperature and refrigerating capacity. The chemical formula of the Gd-based amorphous nanocrystal composite is GdaFebAlc, wherein a, b and c refer to atom contents of corresponding elements, a is larger than or equal to 75 and smaller than or equal to 92, b is larger than or equal to 5 and smaller than or equal to 20, c is larger than or equal to 4 and smaller than or equal to 15, and the equation of a+b+c=100 is met. Compared with the prior art, the Gd-based amorphous nanocrystal composite has the high Curie temperature, and meanwhile has the large magnetic entropy change, the Curie temperature of the composite is more than 200 K, the magnetic entropy change under a 5 T magnetic field is larger than 5.0 J/kg/K, the magnetic transition temperature interval is large, and the refrigerating capacity reaches up to 690 J/kg or above. Thus, the composite is a good magnetic refrigeration material and can be applied as a near room temperature magnetic refrigeration working medium.

The invention discloses a magnetic thermosensitive material manganese-doped holmium iron oxide as well as preparation methods of monocrystalline and polycrystalline thereof. A solid reaction method is carried out with Ho2O3, MnO2 and Fe2O3 powder for synthesis of a HoFe1-xMnxO3 polycrystalline material, and the polycrystalline material grows into a monocrystalline material by an optical-floating-zone furnace method. Applied magnetic fields are not needed for assisting the magnetic thermosensitive material, magnetic transition temperature has a high susceptibility, the magnetic transition critical temperature can be adjusted for usage of the material at room temperature, and the material can be applied to a magnetic thermosensitive device. Ratio of the magnetic thermosensitive material can be changed, in order to obtain different materials whose magnetic transition critical temperature range is between -213.15 to 29.17 DEG C, so that the magnetic transition speed of the material is higher than the magnetic transition speed of the traditional material whose magnetic transition critical temperature is around the Curie temperature, and spontaneous magnetization happens at the temperature above the critical temperature, so that applied magnetic fields are not needed for induction before and after transition. The magnetic thermosensitive material is better than the traditional magnetic thermosensitive device material whose magnetic transition depends on the Curie temperature.

The invention discloses a rare-earth palladium-magnesium low-temperature magnetic refrigeration material and a preparation method thereof. The material has the chemical general formula as follows: RE4-Pd-Mg, wherein RE is one or two selected from Ho, Er and Tm, and the atomic ratio of RE to Pd to Mg is equal to 4:1:1; and the preparation method comprises the steps of (1) mixing; (2) sealing an environment by using inert gases; (3) sintering, namely keeping a quartz vessel at the temperature of 850-920 DEG C for 10-20min, then, cooling to 650-720 DEG C, keeping the temperature for 3-5h, and naturally cooling; (4) tabletting and molding; and (5) sealing and annealing, namely sealing the molded material into a quartz tube, annealing at the temperature of 660-700 DEG C for 36-48h, and naturally cooling to obtain a finished product. The material disclosed by the invention is obvious in magnetic entropy change, high in magnetic refrigeration capacity and favorable in magnetic and thermal reversibility; and the change of magnetic transition temperature and the maximum magnetic entropy change value along with components within the temperature range of 5-40K is continuously adjustable. Slow temperature rise and step-by-step reaction are adopted in the method disclosed by the invention, so that Mg volatilization is overcome; and the method is simple in process and easy to realize.

The invention discloses a Gd-Ni-Al-based amorphous and nanocrystalline composite material. The molecular formula of the Gd-Ni-Al-based amorphous and nanocrystalline composite material is GdaNibAlc, wherein a, b and c represent atom contents of corresponding elements, 80<=a<=90, 5.8<=b<=11.6, 4.2<=c<=8.4, and the equation that a+b+c=100 is satisfied. The Gd-Ni-Al-based amorphous and nanocrystalline composite material is of an amorphous/nanocrystalline complex phase structure and has two refrigeration temperature zones and one or two magnetic entropy change platforms, the high-temperature magnetic order temperature is 270 K or above, and the magnetic entropy change under a 5T magnetic field can reach 6.7 J/kg/K. Because magnetic transition temperature intervals are wide, the refrigeration capacity reaches up to 640 J/kg or above, and the Gd-Ni-Al-based amorphous and nanocrystalline composite material is a good magnetic refrigeration material and can be used as a magnetic refrigeration working material in the two intervals of the two refrigeration temperature zones.

The invention discloses a GdTbHoEr material with high saturation magnetization. The GdTbHoEr material is prepared by taking Gd, Tb, Ho and Er as raw material and carrying out electric arc melting, wherein the chemical formula of the material is GdTbHoEr, and the material with high saturation magnetization has a single close-packed hexagonal crystal structure; and the element components further comprise one or two of La and Y. When being used as a magnetic material, the material has the magnetic phase transformation characteristic, and the saturation magnetization reaches 290-300 emu/g when thetemperature is lower than the Neel temperature; the high-entropy alloy GdTbHoEr is used as a matrix, La and Y are added, the magnetic transition temperature of the alloy is regulated and controlled within the range of 190 K-120 K, and the coercive force of the alloy is regulated and controlled within the range of 600 Oe -1706 Oe. The high-saturation magnetization intensity material has the characteristics of high magnetization intensity, wide existing temperature range, adjustable components, adjustable Neel temperature, simple and diversified process and low overall preparation cost, and issuitable for industrial production.

The invention discloses an anti-perovskite material with room-temperature magnetic refrigeration performance and a preparation method and application thereof, the chemical structural formula of the anti-perovskite material is M < 1-x > NFe < 3 + x >, M is a doped metal selected from one of Ga, Ge, Sn or Zn; n is nitrogen, Fe is iron, and x is more than or equal to 0 and less than or equal to 0.4. The invention also discloses a preparation method of the material and application of the material as a room-temperature magnetic refrigeration material in the field of room-temperature magnetic refrigeration. According to the invention, the content and occupation condition of magnetic ions are changed in an atom doping substitution mode, the exchange effect among the magnetic ions in a system is enhanced, the magnetic transition temperature and saturation magnetization are greatly improved, and the anti-perovskite material with room-temperature magnetic refrigeration capability and high refrigeration performance is obtained. The preparation method provided by the invention is simple to operate and low in cost, and has huge application potential and prospect.