Electrically driven magnetism on a Pd thin film

Abstract

Using first-principles density-functional calculations, we demonstrate that ferromagnetism can be induced and modulated on an otherwise paramagnetic Pd metal thin-film surface through application of an external electric field. As free charges are either accumulated or depleted at the Pd surface to screen the applied electric field, there is a corresponding change in the surface density of states. This change can be made sufficient for the Fermi-level density of states to satisfy the Stoner criterion, driving a transition locally at the surface from a paramagnetic state to an itinerant ferromagnetic state above a critical applied electric field, E c . Furthermore, due to the second-order nature of this transition, the surface magnetization of the ferromagnetic state just above the transition exhibits a substantial dependence on electric field, as the result of an enhanced magnetoelectric susceptibility. Using a linearized Stoner model, we explain the occurrence of the itinerant ferromagnetism and demonstrate that the magnetic moment on the Pd surface follows a square-root variation with electric field, m ϰ ͑E − E c ͒ 1/2 , consistent with our first-principles calculations.

Large magnetoelectric effect in ferroelectric/piezomagnetic heterostructures

“…Recently it was demonstrated that ME effect can be induced by free carriers 6 . In this case, due to spin-dependent screening 7 , an applied electric field produces an accumulation of spin-polarized electrons or holes at the metal-insulator interface resulting in a change of the interface magnetization 8 and the exchange splitting [9][10][11] .…”

Electric field effect on magnetism in metallic ultra-thin films

“…However, this concept may be realized with metals that are similar to ferromagnets. Among these metals, Pd is a nonmagnetic metal that nearly satisfies the Stoner criterion [34][35][36][37]. Ab-initio calculations have shown that the peak of the density of states of bulk nonmagnetic Pd is located at an energy near the Fermi level [34], suggesting that an applied electric field may affect the magnetic state in Pd [37].…”

“…Among these metals, Pd is a nonmagnetic metal that nearly satisfies the Stoner criterion [34][35][36][37]. Ab-initio calculations have shown that the peak of the density of states of bulk nonmagnetic Pd is located at an energy near the Fermi level [34], suggesting that an applied electric field may affect the magnetic state in Pd [37]. Although the modulation of paramagnetic properties was observed in Pt thin films using the EDL capacitor [38], electric-field-induced ferromagnetism has not been reported in nonmagnetic metals.…”

Ferroelectric Field Effect Control of Magnetism in Multiferroic Heterostructures

“…The nature of the magnetoelectric effect due to charge screening can be distinguished between (i) enhanced spin imbalance at the Fermi level due to screening and the corresponding modification in the magnetic moment of the system as a function of the electric field Zhang (1999); (ii) changes in magnetic moment due to changes in electronic bonding at the polarized dielectric interface Duan et al (2006); (iii) changes in the magnetic order with the charge density Gerhard et al (2010); Kudasov & Korshunov (2007); Ovchinnikov & Wang (2008); Sun et al (2010); Vaz et al (2010b), whereby the magnetic state of the system is modified due to changes in the charge carrier density, either between magnetic and non-magnetic states, or between states with different magnetic spin configurations; and (iv) changes in the magnetic anisotropy that lead to different global magnetic states for different applied electric fields Maruyama et al (2009);Niranjan et al (2010).…”

“…A related effect has been predicted for Pd, which is known to be a paramagnetic system with a Stoner parameter slightly short of fulfilling the condition for ferromagnetism by about 5-10%. First principles calculations suggest that depleting the Pd interface of charge carriers by means of an applied electric field can bring the Fermi level down and increase the density of states to favor an exchange-split (magnetic) state Kudasov & Korshunov (2007); Sun et al (2010). A scheme for making the interfacial magnetoelectric effect additive consists of breaking the symmetry of ferromagnetic/dielectric bilayer structures by adding a non-magnetic metal at the other interface of the dielectric; this has been proposed by Cai et al (2009), who have carried out ab initio calculations for Fe, Co, Ni, CrO 2 /BaTiO 3 /Pt systems to demonstrate this procedure (see Table 1).…”