Revealing magnetic and physical properties of TbFe_4.4Al_7.6: experiment and theory

Abstract

We report on the magnetic, electrical transport, caloric and electronic structure properties of TbFe4.4Al7.6 polycrystalline alloy using experiment and theory. The alloy crystallizes in tetragonal structure with I4/mmm space group with lattice parameters a = b = 8.7234(5) Å and c = 5.0387(6) Å. It is ferrimagnetic with a compensation temperature of T cmp ∼ 151 K, Curie-Weiss temperature θ CW ∼ 172.11 K and an effective magnetic moment μeff = (2.37±0.07) μB/f.u with Z = 2. At low temperatures, kinetic arrest-like first-order phase transition is realized through the thermal hysteresis between field-cooled cooling and field-cooled warming curves of M(T) and virgin curves of M(H) and ρ(H) which are outside the hysteresis loops with metamagnetic transition. The high magnetic field suppression of multiple transitions and reduced coercive field H coer and remnant magnetization M rem with increasing temperature are reported. H coer and M rem cease to exist above the compensation temperature T cmp. A correlation between the isothermal magnetization and resistivity is discussed. Specific heat C(T) analysis reveals a Sommerfeld parameter of γ = 0.098 J.mol-1.K-2 and a Debye temperature of θ D ∼ 351.2 K. The sample is metallic as inferred from the ρ(T) behavior and Sommerfeld parameter. The magnetoresistance of the alloy is low and negative which indicates the suppression of weak spin-fluctuations. This alloy avoids the tricritical point despite first-to-second order phase transition. The electronic and magnetic structure calculations, by making use of full potential linearized augmented plane wave (FP-LAPW) method, suggest metallic ferrimagnetic ground state of TbFe4.4Al7.6 with Tb atoms contributing ferromagnetically (5.87 μB) and Fe atoms with antiferromagnetic contribution (2.67 μB), in close agreement with the experimental observation.