Magnetostriction and thermal expansion of HoFe11−xCoxTi intermetallic compounds

Abstract The thermal expansion and magnetostriction of the HoFe 11− x Co x Ti (0≤ x ≤11) alloys have been investigated, using the strain gauge technique in the temperature range 77–600 K. Both thermal expansion and thermal expansion coefficient exhibit an anomalous behaviour and Invar effect below Curie temperature ( T C =516 K) in sample with x =0. The increase of x in HoFe 11− x Co x Ti system leads to disappearing of the Invar effect and increasing of the average thermal expansion coefficient from 6.370×10 −6 K −1 in x =0 to 10.735×10 −6 K −1 in x =11 below room temperature. In addition, the spontaneous volume magnetostriction decreases with Co content. The magnetostriction compensation point is observed in the anisotropic magnetostriction curve of all samples. The maximum value of anisotropic magnetostriction (Δ λ≈ 50×10 −6 ) at room temperature is observed in sample with x =9. The saturation behaviour only appears in samples with x =5, 7 and 9. In samples with x =3, 5 and 7, a noticeable volume magnetostriction (Δ V / V ) is observed in low temperature due to first-order magnetisation process. Moreover, Δ V / V exhibits a large anomaly about 45×10 −6 and 20×10 −6 around room temperature related to spin reorientation transition in samples with x =9 and 11, respectively. The results are discussed based on the local magnetic moment model and irreducible magnetoelastic coupling modes.