High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb

Abstract

CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high (∼ 47%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane is strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.

Magnetism and site exchange in CuFeAs and CuFeSb: A microscopic and theoretical investigation

“…Polycrystalline specimens of CuFeAs and CuFeSb were prepared as described elsewhere [25,26]. For μSR we used the same samples as previously described by Thakur et al [26], whereas for neutron diffraction a new sample was synthesized.…”

“…So far, ferromagnetism of the transition metal ions was only observed in Co based materials LaOCoP and LaOCoAs [23] until 2012, when CuFeSb was synthesized by Qian et al [24]. CuFeSb is a soft ferromagnet, which shows a high spin polarization and a large anion height of h anion = 1.84-1.89Å [24,25], vindicating the theories. Aside from the unique itinerant ferromagnetism of an iron pnictide in general, it is remarkable that a transition metal like Cu occupies the alkali ion position, opening an alternative route for the search of novel materials in the framework of ironbased superconductivity.…”

Breakdown of Hund's rule for CuFeAs

“…The height is comparable to h Te ∼ 1.75Å of Fe 1.068 Te which also shows bicollinear antiferromagnetic order [58]. However, it is smaller than h Sb ∼ 1.84Å of CuFeSb where ferromagnetism is observed [43,44].…”

“…The contradiction raises a great challenge to the existing theory [34,42], which seems valid for the whole family of ironbased superconductors including both iron pnictides and iron chalcogenides, where various magnetic ground states can be correctly accounted for after different anion height is considered. In fact, the theory of anion height is also true for a sister compound of CuFeAs, so called CuFeSb, where DFT calculations [28] and experiments [43,44] both obtained a FM ground state, which can be attributed to a very high anion height of > 1.84Å. Therefore, it is urgent to understand why CuFeAs with intermediate value of anion height is so extraordinary that DFT calculations can not agree with experimental findings even qualitatively.…”

Strong spin depolarization in the ferromagnetic Weyl semimetal Co3Sn2S2 : Role of spin-orbit coupling

“…In this paper, we report on the measurement of transport spin polarization in Co 3 Sn 2 S 2 by spin-resolved point contact Andreev reflection (PCAR) spectroscopy [9][10][11][12][13][14]. Our * goutam@iisermohali.ac.in measurements show that, contrary to the expectation within band-structure calculations, the transport spin polarization in Co 3 Sn 2 S 2 is ∼50%, not 100%.…”