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Elasticity and Antiferromagnetism of Metallic Antiferromagnetics R Elasticity and antiferromagnetism of metallic antiferromagnetics R. Street, J.H. Smith To cite this version: R. Street, J.H. Smith. Elasticity and antiferromagnetism of metallic antiferromagnetics. J. Phys. Radium, 1959, 20 (2-3), pp.82-87. 10.1051/jphysrad:01959002002-308200. jpa-00236072 HAL Id: jpa-00236072 https://hal.archives-ouvertes.fr/jpa-00236072 Submitted on 1 Jan 1959 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. LE ,TOURNA1. DE PHYSIQUE ET LE RADIUM TOME 20, FÉVRIER 1959, 82 ELASTICITY AND ANTIFERROMAGNETISM OF METALLIC ANTIFERROMAGNETICS By R. STREET and J. H. SMITH, Department of Physics, The University, Sheffield, England. Résumé. 2014 On peut prévoir une variation du module d’Young avec la température au point de Néel sur les substances antiferromagnétiques. Nous donnons ici les résultats des mesures rela- tives aux alliages CuMn(03B3) et aux alliages CuMn à plusieurs phases (03B1 + y) On trouve sur ces derniers la variation prévue due à Mn 03B1 et également une anomalie, vers 130 °K, attribuée à la présence de MnCu y précipité. Cette dernière phase est ferromagnétique au-dessous de 130 °K. Une variation régulière avec la température du module d’Young de Pd confirme le fait qu’aux basses températures Pd ne serait pas antiferromagnétique. Abstract. 2014 If an antiferromagnetic is spontaneously deformed on cooling through the Néel temperature, then the application of an external stress results in a redistribution of domain vectors, e.g. they may rotate or antiferromagnetic domain walls may move. This causes an additional strain component which will be apparent as an anomalous variation of the Young’s modulus with the temperature. The results of measurements of the temperature dependence of Young’s modulus for antiferromagnetic 03B3-CuMn alloys and mixed phase (03B1 + 03B3) CuMn alloys are reported. The (03B1 + y) alloys show (a) a Young’s modulus variation of the expected form which is due to the contained 03B1-Mn, (b) a Young’s modulus anomaly at about 130 °K associated with the preci- pitated 03B3-CuMn (containing 40 atomic percent Mn). It is shown that the latter phase below 130 °K exhibits ferromagnetic characteristics. A smooth temperature variation of Young’s modulus has been obtained for Pd which is consistent with the assumption that Pd is not antiferromagnetic at low temperatures. Introduction. - The dependence of Young’s 1950) and thus exhibit antiferromagnetostriction. modulus on the state of magnetization of ferro- Neutron diffraction studies show that the direc- magnetic materials has been known for many tions of antiferromagnetism generally coincide with years, the phenomenon is known as the AE-effect. crystallographic directions of low order. It is For a ferromagnetic of non-zero magnetostriction therefore possible for boundary walls separating an external stress Z in general affects the distri- domains having different directions of antiferro- bution of the magnetization vectors, by rotating magnetism to move and the directions of antiferro- them away from preferred axes or by domain magnetism to rotate away from preferred direc- boundary movement, and the resultant rate of tions under the influence of an external stress. change of intensity of magnetization with stress Measurements of the temperature variation of (è)l/è)Z)H is equal to the rate of change of magneto- Young’s môdulus of pressed bars of cobalt and strictive deformation with field (è)À/H)z. When nickel oxides show a very pronounced decrease in an external stress is applied, in addition to the modulus near the Néel temperatures of the two normal elastic strain of the lattice, e, there is materials (Street and Lewis, 1951 ;g Fine, 1953). another component of strain, cm, produced by the The object of this communication is to report some magnetostrictive deformation accompanying the observations made recently on the temperature redistribution of the magnetization vectors. At variations of Young’s modulus of metallic antifer- magnetic saturation, the magnetization vectors are romagnetic materials. all aligned along the field direction, hence è)À/è)H = )7/t)Z = 0 and E is the only component Expérimental. - The method of measurement of strain produced by the stress Z. Thus in the was similar to that described by Zacharias (1933). unsaturated state the value of Young’s modulus The specimens, of rectangular cross section ZI(F- + Sjn) is less than its value at magnetic satu- 2.00 mm X 3.00 mm, were cemented to quartz ration. crystals, of identical cross section, which were cut It follows that in zero applied field the Young’s so that longitudinal vibrations along the length of modulus of a ferromagnetic should decrease when the composite oscillator were excited by an alter- cooled through the Curie temperature. Above the nating p.d. applied to electrodes deposited on Curie temperature no spontaneous ferromagnetic opposite side faces of the crystal. The resonant order exists and e;m = 0 ; below the Curie tempe- frequencies of oscillation of the composite oscil- rature e;m =1= 0. lator, f o, are given by the relation X-ray techniques have been employed to show that antiferromagnetic materials are spontaneously deformed when they are heated or cooled through their Néel temperatures (Tombs and Rooksby, where fa, fq are respectively the fundamental fre- Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphysrad:01959002002-308200 83 quencies of resonant longitudinal oscillation of the temperature for two typical alloys of this series are spécimen and the quartz crystal alone ; ms, mq are shown in Figure 1. As expected, these curves the masses of the specimen and the crystal. Experi- show pronounced minima which occur at the tran- mentally f o and f q are measured as functions of sition temperature of the alloys. temperature from which ’ /8 may be calculated. The interpretation of the results obtained is Hence Young’s modulus is determined by the rela- uncertain in view of the fact that Tt TN. tion ’ However, investigations of the stress dependence of the intensity of the (110) (magnetic) neutron dif- fraction et loc. that and were to be peak (Bacon al., cit.) suggests ts f, always arranged very strain nearly equal adjusting the length of the the additional component Em in the antiferro- by speci- state arises from wall move- men and various magnetic boundary by using quartz crystals having from of values of In this the effect of ment rather than rotation domain magne- f q. way, perturbing tization vectors. walls the adhesive at the of the and Only boundary separating junction crystal domains directions of antiferro- specimen was minimized: having digerent will move on the of an The oscillator was mounted in an magnetism application composite external stress. Other domain exist -enclosure which could be evacuated or filled with types may e.g. if a line within a domain the direc- low helium as a heat exchanger and means along spin pressure tions are a wall occur of or was t 1 t 1 t t, boundary may heating cooling were It pos- " provided. domains such that on sible to determine relative values of between " changed-step Young’s wall modulus to within 1 in 104. moving through the the spin directions are part formally represented by t t t t t t t t t. The Results and discussion two domains separated by a boundary of this type have the same antiferromagnetostrictive strain the of stress will Cu-Mn Alloys. - The antiferromagnetic pro- along any direction, application not result directly in wall movement and the perties of single y CuMn alloys containing phase contribution to will be zero. From the more than about 70 atomic of z. expres- percent manganese sions for the modulus summarized have been investigated by Bacon et al. (1957). Young’s change in the it will be seen that when domain Below a transition temperature, Tt, which depends Appendix movements are involved of on the are boundary comparison composition, alloys antiferromagnetic results with theoretical is and have a face-centred tetragonal structure. At experimental predictions difficult as of the area of domain walls the transition temperature the alloys undergo a knowledge and the forces impeding wall movement are requir- ed. (oc + y) CuMn Alloys. - It is of interest to inves- tigate the temperature dependence of Young’s modulus of iI..-Mn as a useful preliminary to the consideration of the antiferromagnetic domain structure of the element. The investigation cannot be undertaken directly using pure oc-Mn samples since the material is extremely brittle and cannot be machined into the required regular shape. The difficulty has been overcome in the following way. Starting materials containing various proportions of copper were prepared by melting in an argon arc furnace and then after heating for extended periods of time at temperatures near the melting point they were rapidly quenched, thus retaining the Fie. 1. - Temperature variation qf Young’s modulus for y solid solution. Materials prepared in this way y-CuMn alloys containing 80 and 85 atomic percentage containing as much as 95 atomic percent of manga- Mn., nese were relatively easy to machine and it was possible to produce specimens of the required form martensitic transformation, above Tt they are no from them. The specimens were then trans- longer antiferromagnetic and have a face-centred formed to the mixed (oc + y) phase by heating for cubic structure.
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