<<
>>

§ 1.4. Phase transitions and MKE in materials on the basis of alloys Fe-Rli.

Alloys Fe-Rh concern the magnetocaloric materials showing record values MKE (drawing 1.8.) [71]

In 1938 M.Fallot [72] for the first time has shown, that at rise in temperature ranked magnitomjagky alloy Fe50Rh50 tests phase transition of the first sort from an antiferromagnetic phase (AFM) in the ferromagnetic phase (FM).

This transition occurs at temperature T~320K and is accompanied by volume magnification approximately on l % [73-74].

Phase transition shows a temperature hysteresis and temperature field of coexistence of two phases: AFM and FM [75]. Radiographic examinations have shown, that transition AFM-FM is isostructural [76]. As at transition AFM-FM at heating,

Drawing 1.8. The adiabatic change of temperature (Δμ 0H = 2Т) for several most explored magnetic coolants at temperature of their magnetic transition (materials with transition of the second sort are scored by the shading, the first sort - continuous pouring) [71]

And return transition FM-AFM at cooling alloys show effect of storage of temperature [77].

According to literary data [78], in alloys Fe-Rh (with concentration Rh of 47-53 %) transition from AFM states in FM in a gamut of temperatures T = 310-360 To with the subsequent transition from FM a state in paramagnetic in the field of temperature Tc~633 To (drawing 1.9) is observed.

It is necessary to score, that temperatures FP, quantities of magnetisation and MKE depend not only on a relation of concentrations Fe and Rh, but also from technological requirements of reception of alloys, and also modes of the further heat treatment (otzhig, a temper, etc.). Therefore the unequivocal allocation of a concrete composition as a material with record value MKE is not absolutely correct, as it is necessary to spend comparison of samples of different compositions, but with one report of heat treatment. One of first found out record values MKE corresponds to composition Fe49Rh51 which observed datas are given in drawing 1.9 [56].

Apparently, temperature dependence MKE for tempered sample Fe49Rh51имеет a narrow view in comparison with otozhzhyonnym, and peak MKE, found out in the field 1,95 Tl corresponds to values-12,9 To and 3,5 To for tempered and otozhzhyonnogo samples accordingly. It is necessary to pay attention, that alloys Fe-Rh show subzero MKE, i.e. at change of the enclosed magnetic field the sample is cooled.

Change of quantity of the adiabatic change of temperature depending on change of magnetic field AT/AN - parametre which allows to estimate MKE, for Fe49Rh51находится in limits between-6,6 To/tl and-8,3 To/tl for otozhzhyonnogo the sample and-12,9 To/tl for the tempered.

Drawing 1.9. Temperature dependences of the adiabatic change of temperature ΔT alloys Fe049Rh0 si in magnetic fields 0,65 Tl, 1,25 Tl, 1,7 Tl and 1,95 Tl, presented to operation [56]: figures () correspond otozhzhennomu to the sample; figures (•) correspond to the tempered sample.

Dependence of magnetisation, maximum of change of temperature and temperature of magnetic transition from heat treatment requirements it has been shown in operation [81] (drawing 1.10). Apparently from drawing 1.10 rise in temperature otzhiga to 1423 To biass temperature of magnetic transition towards low temperatures and reduces breadth of a temperature hysteresis. Quantity of magnetisation and change of magnetic entropy thus decreases, that is related to relation change αzи γ phases owing to high-temperature heat treatment.


zo

Drawing 1.10. Temperature dependence of magnetisation and change of entropy for alloy Fe47Rh53 [81].

In operations [79-80] calculations according to the basic contributions in MKE in the field of AFM-FM transition on the basis of the thermodynamic theory have been executed. The carried out calculations for contributions of a magnetic field energy, energy of anisotropy, an exchange energy and magnetoelastic energy have shown, that the spotting contribution to change of blanket magnetic entropy ΔSm makes change of a magnetic exchange energy. It has been shown, that the magnetic field energy almost does not import the contribution in ΔSm5а the contribution of energy of a magnetic anisotropy is inappreciable.

<< | >>
A source: Rodionov Vladimir Vladimirovich. MAGNETOCALORIC EFFECT of PERMANENT-MAGNET COMPOSITES ON THE BASIS OF ALLOYS Fe-Rh. The dissertation on competition of a scientific degree of the candidate of physical and mathematical sciences. Kaliningrad - 2018. 2018

More on topic § 1.4. Phase transitions and MKE in materials on the basis of alloys Fe-Rli.:

  1. Chapter 1. DOMAIN STRUCTURE of the FERROMAGNETIC ALLOYS gejslera And RARE-EARTH INTERMETALLIC COMPOUNDS In the field of MAGNETIC PHASE TRANSITIONS
  2. GRECHISHKIN Rostislav Mihajlovich. DOMAIN STRUCTURE of the FERROMAGNETIC ALLOYS gejslera And RARE-EARTH INTERMETALLIC COMPOUNDS In the field of MAGNETIC PHASE TRANSITIONS. The dissertation on competition of a scientific degree of the doctor of physical and mathematical sciences. Tver - 2016, 2016
  3. Grechishkin Rostislav Mihajlovich. DOMAIN STRUCTURE of the FERROMAGNETIC ALLOYS gejslera And RARE-EARTH INTERMETALLIC COMPOUNDS In the field of MAGNETIC PHASE TRANSITIONS. The dissertation AUTHOR'S ABSTRACT on competition of a scientific degree of the doctor of physical and mathematical sciences. Tver - 2016, 2016
  4. 1.4.3.3. Complex DS in magnetics with orientation phase transitions.
  5. § 1.3. Alloys on an iron and rhodium bottom (Fe-Rh). The phase diagramme, structure and magnetic properties.
  6. About practical aspects of modelling of phase transitions of the first sort in nanoklasterah metals
  7. chapter 1. Theoretical and experimental researches of phase transitions of the first sort in metal nanosistemah
  8. phase transitions pirohlor - perovskit I, perovskit I - perovskit II and their influence on electrophysical properties of films PZT (54∕46)
  9. § 1.2. Magnetocaloric effect in materials with phase transition of the first sort.
  10. features of exchange bias in thin-film structures on the basis of alloys NiFe and IrMn.
  11. Reliability of devices of phase storage and communication with the physicochemical propertiesof materials
  12. CHAPTER 4. FEATURES OF PERMANENT-MAGNET AND MAGNETOCALORIC EFFECTS IN THICK-FILM COMPOSITES ON THE BASIS OF ALLOYS Fe-Rh
  13. Working out of the program of the analysis of a file of meshes of non-volatile phase storage (JAEFP) on the basis of HSPcomposition GST-225
  14. Rodionov Vladimir Vladimirovich. MAGNETOCALORIC EFFECT of PERMANENT-MAGNET COMPOSITES ON THE BASIS OF ALLOYS Fe-Rh. The dissertation on competition of a scientific degree of the candidate of physical and mathematical sciences. Kaliningrad - 2018, 2018
  15. Rodionov Vladimir Vladimirovich. MAGNETOCALORIC EFFECT of PERMANENT-MAGNET COMPOSITES ON THE BASIS OF ALLOYS Fe-Rh. The dissertation AUTHOR'S ABSTRACT on competition of a scientific degree of the candidate of physical and mathematical sciences. Kaliningrad - 2018, 2018
  16. 1.1. Processes with preliminary restoration of iron in a solid phase and to-restoration in a solution phase
  17. CHAPTER 4. MODELLING OF ORGANO-INORGANIC MATERIALS AND NANOKOMPOZITOV ON THEIR BASIS
  18. § 1.6. MKE in permanent-magnet composites and prospects of their application.