Exchange bias-like effect in TbFeAl induced by atomic disorder

Abstract

Exchange bias-like effect observed in the intermetallic compound TbFeAl, which displays a magnetic phase transition at T h c ≈ 198 K and a second one at T l c ≈ 154 K, is reported. Jump-like features are observed in the isothermal magnetization, M (H), at 2 K which disappear above 8 K. The field-cooled magnetization isotherms below 10 K show loop-shifts that are reminiscent of exchange bias, also supported by training effect. Significant coercive field, Hc ≈ 1.5 T at 2 K is observed in TbFeAl which, after an initial increase, shows subsequent decrease with temperature. The exchange bias field, H eb , shows a slight increase and subsequent leveling off with temperature. It is argued that the inherent crystallographic disorder among Fe and Al and the high magnetocrystalline anisotropy related to Tb 3+ lead to the exchange bias effect. TbFeAl is recently reported to show magnetocaloric effect and the present discovery of exchange bias makes this compound a multifunctional one. The result obtained on TbFeAl generalizes the observation of exchange bias in crystallographically disordered materials and gives impetus for the search for materials with exchange bias induced by atomic disorder. PACS numbers:Reviews on exchange bias [1][2][3][4] in materials point toward the importance of this effect in read-heads in magnetic recording,[5] giant magnetoresistive random access memory devices [6] and in permanent magnets. [7] Interpreted as phenomena occurring at the interface between magnetically ordered microscopic regions, exchange bias interfaces can be ferromagnetic/antiferromagnetic or ferromagnetic/antiferromagnetic/spin-glass. Mixed magnetic interactions are deemed to be an important ingredient for this effect to occur. Recent work [8] promotes the importance of ferromagnetic spin structure in exchange bias and explains some of the anomalous features of exchange bias field. In this Letter we report on the observation of exchange bias-like effect in TbFeAl. RFeAl (R = rare earth) were first investigated by Oesterreicher.[9-11] Only the heavier rare earths were observed to form the stable MgZn 2 -type structure. TbFeAl is recently identified as a magnetocaloric [12] (albeit, a weak effect) which becomes a possibel "multifunctional" compound with the observation of exchange bias.As noted above, TbFeAl crystallizes in hexagonal MgZn 2 type crystal structure with P 6 3

Magnetic phenomena in equiatomic ternary rare earth compounds

“…A promising material for magnetic refrigeration application, TbFeAl was also reported to show large exchange bias, making it a multifunctional material [59]. The results suggest that the exchange bias in TbFeAl is induced by the inherent crystallographic disorder between Fe and Al and strong magneto-crystalline anisotropy of Tb 3+ [59]. These results pave the way for search of materials exhibiting exchange bias induced by atomic disorder.…”

“…The saturation moment in FM GdFeAl is found to be 5.8 µB/f.u., lower than the theoretical value of Gd 3+ ion [58], indicating no moment from Fe, however FM ordering in non-magnetic rare earth compounds such as YFeAl and LuFeAl suggest magnetic moment contribution from Fe atoms. A promising material for magnetic refrigeration application, TbFeAl was also reported to show large exchange bias, making it a multifunctional material [59]. The results suggest that the exchange bias in TbFeAl is induced by the inherent crystallographic disorder between Fe and Al and strong magneto-crystalline anisotropy of Tb 3+ [59].…”