Soft X-ray Magnetic Circular Dichroism Research Articles

Magnetic structure of Fe/Cr/Fe trilayers.

Soft x-ray magnetic circular dichroism (SXMCD) is used to determine independently the magnetic behavior of each layer of Fe/Cr/Fe trilayers deposited on GaAs(001). Submonolayer coverages of Cr on Fe(001) films are found to be ferromagnetic and antialigned to the Fe moment. Subsequent Cr deposition shows a monotonically decreasing total moment, consistent with island growth of ferromagnetic Cr sheets antialigned with adjoining Cr layers. For thin Cr interlayers, the second Fe film is antialigned with the first Fe film, but a second Fe film of less than 2-ML thickness shows no SXMCD signal

Magnetic circular dichroism of FexCo1−x alloy single crystal thin films (abstract)

Soft x-ray magnetic circular dichroism (SXMCD) of the L2 and L3 edges is used to independently determine magnetic information for single crystal FexCo1−x alloy thin films (0≤x≤1) grown on ZnSe(001). Similar to surface magneto-optical Kerr effect (SMOKE) but with element and site specificity, SXMCD, which is the difference between the absorption of left and right circularly polarized soft x rays, can be used to determine a variety of magnetic parameters including spin-orbit and exchange interaction energies. Measurements made at the National Synchrotron Light Source (NSLS) U4B beamline on the Fe–Co alloy system exhibit unique changes in SXMCD signal as a function of alloy concentration. The SXMCD signal is found to rise linearly with reducing atomic concentration for both the Co and Fe. At the dilute limit of 10% FE (x=0.1), the Fe L3 SXMCD is found to increase by almost a factor of three to near 40%. In some Fe/Co structures, the largest reported SXMCD values in excess of 70% are observed! This example shows the utility of SXMCD in obtaining magnetic information in alloy systems in an element specific and even site specific manner.

Soft x-ray magnetic circular dichroism (invited) (abstract)

Recent developments in synchrotron radiation instrumentation have made possible the production of high quality circularly polarized light in the soft x-ray region (150–1500 eV).1,2 Magnetic circular dichroism (MCD), the difference in the absorption intensity of magnetic systems using left- and right-circularly polarized light, has been exploited in the visible, VUV, and hard x-ray spectral regions to provide valuable information on the electronic and magnetic properties of magnetically oriented systems. Soft x-ray magnetic circular dichroism (SXMCD) has several advantages over the VUV and hard x-ray spectral regions: the major electronic states that are responsible for magnetism, i.e., the 3d states of transition metals and the 4f states of rare-earth elements, can be reached via strong dipole transitions from their respective well-separated 2p3/2, 2p1/2, and 3d5/2, 3d3/2 sharp core levels. Compared to MCD in the visible region, known as the magneto-optical Kerr effect, SXMCD offers element and site specificity with relatively easier data interpretation. A brief review of the principles of SXMCD2 and current instrumental developments will be given. SXMCD measurements conducted at the Dragon beamline on a wide variety of magnetic systems, including transition metals, surfaces, ultrathin films, alloys, ferrites, rare-earth compounds, and biological samples will be utilized to demonstrate the capability of SXMCD as a tool for basic and applied magnetism research.2,3

Magnetic structure of Fe/Cr/Fe trilayers

The magnetic structure of Cr films deposited on single crystal Fe(001)/GaAs(001) substrates is investigated by soft x-ray magnetic circular dichroism (SXMCD) of the L2 and L3 absorption edges. We find that 0.25 ML Cr coverages result in Cr moments aligned with each other and antialigned to the underlying Fe moment direction. The Cr moment is measured to be 0.6±0.2 μB. Additional Cr deposition results in a monotonically reducing averaged moment consistent with the island growth of ferromagnetic Cr sheets of a single layer, antialigned with adjoining sheets. SXMCD measurements of the trilayer structures clearly show the antiferromagnetic coupling of the two Fe films through the interlying Cr film.

Magnetic structure of Fe/Cr/Fe trilayers

The magnetic structure of each layer of Fe/Cr/Fe trilayers deposited on GaAs(001) is determined by soft X-ray magnetic circular dichroism (SXMCD) which is derived from X-ray absorption spectroscopy using circularly polarized light. Submonolayer coverages (0.25 ML) of Cr on Fe(001) films are found to be ferromagnetic and anti-aligned to the Fe moment. Additional Cr deposition shows a monotonically decreasing total moment, consistent with island growth of ferromagnetic Cr sheets anti-aligned with adjoining Cr layers. A second Fe film deposited on thin Cr interlayers is anti-aligned with the first Fe film. A second Fe film of less than 2 ML thickness shows no SXMCD signal.

Soft-X-ray magnetic circular dichroism: a new technique for probing magnetic properties of magnetic surfaces and ultrathin films

We demonstrate the feasibility of applyying the novel soft-X-ray magnetic circular dichroism (SXMCD) technique to investigate the magnetic properties of magnetic surfaces and ultrathin films. Measurements have been carried out on Ni films of various thickness on a Cu(100) substrate at the Ni L 2,3 absorption edges. The SXMCD data exhibit strong temperature and thickness dependence, giving film thickness dependent Curie temperatures and suggesting that a single monolayer of Ni on a Cu(100) substrate may be non-magnetic.

Magnetic moments in a gadolinium iron garnet studied by soft-X-ray magnetic circular dichroism

The magnetic moments of Gd and Fe in gadolinium (Gd 3Fe 5O 12) were probed at 77 and 300 K by soft-X-ray magnetic circular dichroism (SXMCD) measurements at the GdM 4.5 and the FeL 2.3 absorption edges. The SXMCD signal at each edge allows one to independently determine the magnetic ordering for each specific ion, and the temperature dependence confirms that the reversal of the macroscopic magnetization is due to the reversal of each local magnetic moment of the Fe and the Gd atoms when the compensation point ( T comp = 288 K) is crossed. This work therefore demonstrates that SXMCD can probe element and site specific magnetic properties of multi-component systems.

Magnetic properties of ultrathin films of Ni/Cu(001) probed by soft-x-ray magnetic circular dichroism (abstract)

The magnetic properties of MBE-grown ultrathin Ni films on a Cu(001) substrate are investigated using soft-x-ray magnetic circular dichroism (SXMCD) spectroscopic technique. These measurements are carried out by recording Ni L2,3 absorption spectra with highly circularly polarized soft x rays recently obtained at the AT&T Bell Laboratories Dragon synchrotron radiation beamline.1 For low Ni coverages, no MCD effect along the 〈100〉 direction is observed at room temperature, while for intermediate coverages, the MCD effect becomes appreciable and increases to its bulk value at ∼25 ML. With only the assumption that the unoccupied density of states of Ni lie mainly in the minority bands, the amount of the MCD effect can be related to the magnetic moment. The thickness and temperature dependence of the magnetic moment obtained from our SXMCD measurements are compared with those of Ni/Cu(111) obtained from magneto-optical data.2 The advantages and differences between the SXMCD and MOKE techniques are discussed. The novel SXMCD technique allows for element specific magnetic characterization of a variety of interesting structural architectures including 2 D films, dilute impurities, and disordered matrices.

Element specific magnetic moments of gadolinium iron garnet probed by soft-x-ray magnetic circular dichroism (abstract)

The element specific magnetic moments of Gd and Fe in a gadolinium iron garnet (Gd3Fe5O12) were probed at various temperatures by measuring the soft-x-ray magnetic circular dichroism (SXMCD) at the Gd M4,5 and the Fe L2,3 adsorption edges in an external field of 5 kG. The soft-x-ray absorption spectra were recorded with the photocurrent method using highly circularly polarized soft x rays recently obtained at the AT&T Bell Laboratories Dragon synchrotron radiation beamline.1 The temperature dependence of the SXMCD signal at each edge allows one to independently determine the magnetic ordering of each specific ion. Our individually probed magnetic moment of the Gd3+ ion and of the two Fe3+ ions in different sites confirm the earlier calculations which predict a reversal of the local magnetic orientation at ∼280 K. This work demonstrates that SXMCD is a valuable tool for probing the element and site specific magnetic properties of multicomponent systems. The applications of this novel technique to the investigation of transition metals and rare earths in ferromagnetic alloys, compounds, disordered, and impurity systems will be addressed.