Magnetic and Electronic property of transition metal
phosphides interface of NixP/Fe2P
Naoyuki Maejimaa,b,c, Yuma Kuwabaraa, Tomoya Yoshidaa, Takahiro Otaa,
Yuki Shimatoa and Kazuyuki Edamotoa,bab

Coll. Sci., Rikkyo Univ., Tokyo 171-8501, Japan.
Research Center for Smart Molecules, Rikkyo Univ.,Tokyio 171-8501, Japan.
cInstitute for Molecular Science, Okazaki 444-8585, Japan.

Transition metal Phosphide with Fe2P-type structure is promising candidates for magnetic
refrigerant materials.[1] (Fe1-xNix)2P exhibit ferromagnetic properties at room temperature forx < 0.8. The Curie temperature decreases with increasing x and it exhibit a Pauli paramagnet
behavior for x>0.5. [2] The Curie temperature can be controlled by adjusting the ratio of Feand Ni. Additionally, experimental and computational studies suggest that the magnetism of(Fe1-xNix)2P involves mainly the Fe sites and little or no Ni sites. [3] The change in themagnetic properties is consider to involve a change in electronic state due to the Fe and Ni
substitution. However, there are few experimental investigations of magnetic properties andelectronic states about the same system.
Recently, we have succeeded in fabricating Ni phosphide thin films on Fe2P substrates. In
generally, surfaces and interfaces often exhibit different magnetic properties from those in thebulk. It is interesting that the new magnetic properties will appear or not in this transition
metal phosphide thin film and interface, however there is few reports about the magnetic
properties of this kind of materials. In this study, we investigated the magnetic and electronic
properties of the thin films and interfaces of NixP/Fe2P samples using X-ray magnetic circulardichroism (XMCD) and X-ray photoelectron spectroscopy (XPS) measurements.
Fe2P(10-10) were cleaned by cycles of Ar+ ion spattering (0.5 keV) and 750°C annealing.
The cleaned surfaces showed c(2x2) Low energy electron diffraction (LEED) patterns. Niatoms were deposited on the Fe2P clean surface at 500°C, which induces phosphorization of
the film owing to surface segregation of P atoms from the bulk.[4] The thickness of thin film
was controlled by amount of Ni. Prepared NixP/Fe2P samples exhibit c(2x2) LEED pattern.
The XMCD measurement of Fe2P(10-10) and Ni2P(10-10) clean surfaces and NixP/Fe2P thinfilm samples were performed at BL14 of HiSOR at room temperature. The XPS measurementof those samples were performed at BL5U of UVSOR and BL3B of PF.
Firstly, we measured Fe L edge and Ni L edge XMCD spectra of the NixP/Fe2P sample.
The thickness of nickel phosphide layer was estimated 5Å. The Fe Ledge XMCD signal
obtained from the NixP/Fe2P sample was significantly increased from that of clean Fe2P
substrate sample. Ni phosphides such as Ni2P, Ni3P, and NiP3 are paramagnetic,[5] and Ni2P
substrates did not show XMCD signals. On the other hand, NixP/Fe2P samples showed
XMCD signals at the Ni L edge. The peak top energy of the Fe L3 edge of the thin film
sample is lower than that of the Fe2P clean surface and the peak top energy of the Ni L3 edgeof the thin film sample is higher than that of Ni2P clean surface.
Secondly, we measured Fe L edge XMCD spectra obtained from various thickness
NixP/Fe2P samples as shown in Figure1. Thickness dependence of XMCD signal wasconfirmed. These results indicated that the interaction between the thin film and the substratechanged the Curie temperature of the substrate and magnetic property of Ni phosphide thinfilm.

Combining XMCD and XPS results, we will discuss about this relationship of magnetic
and electronic properties NixP/Fe2P samples.

FIGURE 1. Fe L edge XMCD spectra obtained from various thickness NixP/Fe2P samples.

REFERENCES[1] O. Tegus, E. Brück, K. H. J. Buschow, F. R. de Boer, Nature 415 (2002) 150.
[2] J. B. Goodenough et al., J. Appl. Phys. 40 (1969) 3.
[3] R.Zachnetal et al., J. Alloys Compd. 383 (2004) 325[4] Y. Sugizaki et al., Jpn. J. Appl. Phys. 57 (2018) 115701.
[5] K. Zeppenfiled et al., J. Phys. Chem. Solids 54, (1993) 1527.