In this paper we discuss the atomic and magnetic structure of rare earth-transition metal composi... more In this paper we discuss the atomic and magnetic structure of rare earth-transition metal compositionally modulated films with characteristic bilayer thicknesses in the nanometer range. A theoretical model based on singleion anisotropy and anisotropic pair correlations has been developed to understand the occurrence of perpendicular magnetic anisotropy for thin individual layers. Systematics of the magneto-optic properties of this class of materials are discussed, along with recent results on magnetization reversal mechanisms as studied by time decay of the Kerr effect.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
In this paper we report our detailed study on phase formation, phase transformation and magnetic ... more In this paper we report our detailed study on phase formation, phase transformation and magnetic properties of films based on the Co-Sm system with different compositions and heat treated at different temperatures. All films were deposited by DC magnetron sputtering. Two compositions near the Co_5Sm and Co_7Sm2 were selected. All the films have a Cr underlayer of about 95 nm
Systematic studies have been performed on the layer-thickness dependence of magnetization and ani... more Systematic studies have been performed on the layer-thickness dependence of magnetization and anisotropy for amorphous rare-earth-transition-metal compositionally modulated films with characteristic bilayer thicknesses (k) in the range 0.6-3 nm (6-30 A). The results permit for the first time the development of a detailed model for the magnetization and perpendicular magnetic anisotropy as a function of X. Single-ion anisotropy is shown to be the major contributor to the perpendicular anisotropy for Dy/Co and similar systems.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1989
We have extended the technique of varkable angle spectroscopic ellipsomdry to measurement of the ... more We have extended the technique of varkable angle spectroscopic ellipsomdry to measurement of the magneto-optical effects as a function of wavelength and angle of incidence and field strength. Results on DyCo multilayers are reported.
The problem of experimentally determining the uniaxial anisotropy of ferrimagnetic materials near... more The problem of experimentally determining the uniaxial anisotropy of ferrimagnetic materials near the compensation temperature or compensation composition is discussed. As the net magnetization tends toward zero, increasingly stringent field requirements must be met to measure the anisotropy accurately.
ABSTRACT The effects of magnetic layer thickness on film structural and magnetic properties were ... more ABSTRACT The effects of magnetic layer thickness on film structural and magnetic properties were studied systematically with emphasis on the thermal effects on thin recording media films. X-ray diffraction measurements reveal structural changes as thickness decreases, and the existence of a “Cr enriched phase” associated with the interface. The saturation magnetization Ms decreases with thickness and the thickness of the “dead layer” was found to be ∼23Å. Systematic measurements of effective anisotropy, coercivity and saturation magnetization as functions of temperature have been carried out. Magnetic viscosity measurements reveal that thermal stability is affected not only by grain sizes but also by anisotropy reduction associated with nanostructure evolution, as the film thickness decreases.
Co 3 &Pt 10 A) XN (N=S, 16, and 30 bilayers) multilayer thin lilms were prepared by sputtering on... more Co 3 &Pt 10 A) XN (N=S, 16, and 30 bilayers) multilayer thin lilms were prepared by sputtering onto an 850-W-thick SiBI layer that had been deposited on a silicon (111) substrate. We used the polar Kerr effect to measure the time dependence of magnetization reversal over the temperature range 90-300 K. Direct domain observations were also carried out. The results show that the domain expansion process depends strongly on the number of bilayers. Uniform domain expansion was found only in the thinner samples. From the time dependence of the magnetization reversal measurements over the temperature range 90-300 K, the activation energy and volume associated with domain wall motion were found to be 1.2 eV and 2.3 x lo-l8 cm3 for N=8 sample. The N= 16 and N= 30 samples seem to have a broad distribution of activation energies. Our observations suggest. that both the coercivity and magnetization reversal are controlled by the defects that come from the interface between the Co and Pt.
The main feature of an exchange spring magnet can be characterized by ferromagnetic exchange coup... more The main feature of an exchange spring magnet can be characterized by ferromagnetic exchange coupling between a magnetically soft phase and a magnetically hard phase. The coupling constant J, a measure of the coupling strength between the two phases, is a key parameter in controlling the spring magnet properties. A ferromagnetically coupled hard-soft bilayer ͑FCB͒ has been used in this article to develop analytical expressions for a spring magnet that correlate the magnetic properties of a FCB and its layer parameters. These analytical expressions have been developed by solving a modified Stoner-Wohlfarth model. A set of analytical solutions describing the magnetic properties of the FCB at the different stages of J have been derived. The evolution of the magnetization reversal in a FCB, as a function of the coupling constant J, and an applied field H, is analyzed in detail. As a result, the approach to enhance the maximum energy product (BH) max is revealed.
It was found that for the conventional synthetic antiferromagnetically coupled (SAF) media, with ... more It was found that for the conventional synthetic antiferromagnetically coupled (SAF) media, with Co layer thickness dCo=0 Å, the bottom layer is not well ordered ferromagnetically, and that this magnetic ordering is improved significantly for dCo of only ~4 Å. The coupling constant J, as well as magnetic and magnetization reversal properties MS, HC, SFD, Ku, (KuV*/kT), and V* were measured as a function of dCo for both the top and bottom layers. The relationships among these parameters were analyzed.
Magnetic and structural properties of hexagonal-close-packed-(CoCrPt)100−xCx thin films for poten... more Magnetic and structural properties of hexagonal-close-packed-(CoCrPt)100−xCx thin films for potential applications in magnetic recording media have been investigated. CrTi and Cr underlayers were used to improve the in-plane preferred orientation. High coercivity of 4.4 kOe and anisotropy of 3.6×106 erg/cm3 have been achieved in films with a CrTi underlayer after postdeposition annealing. The addition of Ti to the Cr underlayer results in lower annealing temperature and shorter annealing time, while retaining higher coercivity. Vibrating sample magnetometer measurements showed that the magnetic moment lies fairly well in the film plane under proper preparation conditions; while x-ray diffraction measurements showed that the CrTi underlayer promoted Co (10.0) in-plane preferred orientation. Grain isolation in the magnetic layer was improved by the segregated C and further enhanced by postdeposition annealing. The peak value of δM curves decreased upon annealing and changed to a negative value when higher annealing temperatures were applied, indicating that strong exchange coupling in as-deposited film decreased and changed to dipolar interaction dominance upon annealing.
The temperature dependence of the sputtering Ar pressure effects on magnetic properties and the c... more The temperature dependence of the sputtering Ar pressure effects on magnetic properties and the coercivity mechanism of Co(2 &/Pd(13 A) multilayers were studied as the sputtering Ar pressure varied from 3-15 mTorr and the temperature from 300 to 35 K. It is found that the roughness of the interfaces or film surface increases with increasing sputtering pressure, the anisotropy increases with decreasing temperature and increasing Ar pressure and shows a maximum at P,=12 mTorr, and the coercivity increases with Ar pressure and shows stronger temperature dependence at higher Ar pressure. The coercivity mechanism was analyzed in terms of the coercivity predicted by Kronmiiller's theory [Phys. Status Solidi B 144, 385 (1987)]. Wall pinning is found to be the main mechanism and the size of the pinning site increases slightly as the Ar pressure increases.
We report on the magnetic and magneto-optical properties of the intermetallic alloys MnS(Gel-nMXj... more We report on the magnetic and magneto-optical properties of the intermetallic alloys MnS(Gel-nMXj3, where M=Sn, Pb. Generally, these alloys were ordered ferromagnetically at Ta300 K for xcO.3. The structure of Mn,(Ge,-,Sn,)3 remains in the hexagonal Mn,Si,(/zPlh) phase up to x=0.25 and then changes to Ni,In (hP6) as x approaches 1. The magnetization and Curie temperature of these alloys is largest for small x and reach a minimum value near x = 0 .S. The room temperature Polar Kerr rotation, however, increases from-0.06" at s = 0 to maximum value of-0.12" atx=O.I before decreasing toward zero forx>O.3. The M.&Ge,-,Pb,), samples show a Mn,Si, structure with ferromagnetic behavior for x60.3, and varying structure with rapidly decreasing magnetization above x = 0.3. The magnetic behavior observed was compIex for x> 0.3. The Kerr rotation of the Pb-doped alloys in the ferromagnetic region monotonically decreases from-0.06" to zero at x-0.3.
Evolution of orientation distribution of Co͑110͒ crystal planes was determined by x-ray rocking c... more Evolution of orientation distribution of Co͑110͒ crystal planes was determined by x-ray rocking curves. It has been found that: ͑i͒ The full-width at half maximum W of the Co͑110͒ rocking curve decreases with both increasing Cr underlayer thickness d Cr , and increasing CoCrTa magnetic layer thickness d Co , especially in the thin layer regime. ͑ii͒ For the thin d Co regime, the interlayer diffusion between the Cr underlayer and the magnetic layer affects the rocking curves and magnetic properties significantly. ͑iii͒ Film magnetic properties, e.g., a significant jump in coercivity with increasing magnetic layer thickness in the thin d Co regime may be related in part to the evolution of the Co͑110͒ orientation distribution.
In this paper we discuss the atomic and magnetic structure of rare earth-transition metal composi... more In this paper we discuss the atomic and magnetic structure of rare earth-transition metal compositionally modulated films with characteristic bilayer thicknesses in the nanometer range. A theoretical model based on singleion anisotropy and anisotropic pair correlations has been developed to understand the occurrence of perpendicular magnetic anisotropy for thin individual layers. Systematics of the magneto-optic properties of this class of materials are discussed, along with recent results on magnetization reversal mechanisms as studied by time decay of the Kerr effect.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
In this paper we report our detailed study on phase formation, phase transformation and magnetic ... more In this paper we report our detailed study on phase formation, phase transformation and magnetic properties of films based on the Co-Sm system with different compositions and heat treated at different temperatures. All films were deposited by DC magnetron sputtering. Two compositions near the Co_5Sm and Co_7Sm2 were selected. All the films have a Cr underlayer of about 95 nm
Systematic studies have been performed on the layer-thickness dependence of magnetization and ani... more Systematic studies have been performed on the layer-thickness dependence of magnetization and anisotropy for amorphous rare-earth-transition-metal compositionally modulated films with characteristic bilayer thicknesses (k) in the range 0.6-3 nm (6-30 A). The results permit for the first time the development of a detailed model for the magnetization and perpendicular magnetic anisotropy as a function of X. Single-ion anisotropy is shown to be the major contributor to the perpendicular anisotropy for Dy/Co and similar systems.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1989
We have extended the technique of varkable angle spectroscopic ellipsomdry to measurement of the ... more We have extended the technique of varkable angle spectroscopic ellipsomdry to measurement of the magneto-optical effects as a function of wavelength and angle of incidence and field strength. Results on DyCo multilayers are reported.
The problem of experimentally determining the uniaxial anisotropy of ferrimagnetic materials near... more The problem of experimentally determining the uniaxial anisotropy of ferrimagnetic materials near the compensation temperature or compensation composition is discussed. As the net magnetization tends toward zero, increasingly stringent field requirements must be met to measure the anisotropy accurately.
ABSTRACT The effects of magnetic layer thickness on film structural and magnetic properties were ... more ABSTRACT The effects of magnetic layer thickness on film structural and magnetic properties were studied systematically with emphasis on the thermal effects on thin recording media films. X-ray diffraction measurements reveal structural changes as thickness decreases, and the existence of a “Cr enriched phase” associated with the interface. The saturation magnetization Ms decreases with thickness and the thickness of the “dead layer” was found to be ∼23Å. Systematic measurements of effective anisotropy, coercivity and saturation magnetization as functions of temperature have been carried out. Magnetic viscosity measurements reveal that thermal stability is affected not only by grain sizes but also by anisotropy reduction associated with nanostructure evolution, as the film thickness decreases.
Co 3 &Pt 10 A) XN (N=S, 16, and 30 bilayers) multilayer thin lilms were prepared by sputtering on... more Co 3 &Pt 10 A) XN (N=S, 16, and 30 bilayers) multilayer thin lilms were prepared by sputtering onto an 850-W-thick SiBI layer that had been deposited on a silicon (111) substrate. We used the polar Kerr effect to measure the time dependence of magnetization reversal over the temperature range 90-300 K. Direct domain observations were also carried out. The results show that the domain expansion process depends strongly on the number of bilayers. Uniform domain expansion was found only in the thinner samples. From the time dependence of the magnetization reversal measurements over the temperature range 90-300 K, the activation energy and volume associated with domain wall motion were found to be 1.2 eV and 2.3 x lo-l8 cm3 for N=8 sample. The N= 16 and N= 30 samples seem to have a broad distribution of activation energies. Our observations suggest. that both the coercivity and magnetization reversal are controlled by the defects that come from the interface between the Co and Pt.
The main feature of an exchange spring magnet can be characterized by ferromagnetic exchange coup... more The main feature of an exchange spring magnet can be characterized by ferromagnetic exchange coupling between a magnetically soft phase and a magnetically hard phase. The coupling constant J, a measure of the coupling strength between the two phases, is a key parameter in controlling the spring magnet properties. A ferromagnetically coupled hard-soft bilayer ͑FCB͒ has been used in this article to develop analytical expressions for a spring magnet that correlate the magnetic properties of a FCB and its layer parameters. These analytical expressions have been developed by solving a modified Stoner-Wohlfarth model. A set of analytical solutions describing the magnetic properties of the FCB at the different stages of J have been derived. The evolution of the magnetization reversal in a FCB, as a function of the coupling constant J, and an applied field H, is analyzed in detail. As a result, the approach to enhance the maximum energy product (BH) max is revealed.
It was found that for the conventional synthetic antiferromagnetically coupled (SAF) media, with ... more It was found that for the conventional synthetic antiferromagnetically coupled (SAF) media, with Co layer thickness dCo=0 Å, the bottom layer is not well ordered ferromagnetically, and that this magnetic ordering is improved significantly for dCo of only ~4 Å. The coupling constant J, as well as magnetic and magnetization reversal properties MS, HC, SFD, Ku, (KuV*/kT), and V* were measured as a function of dCo for both the top and bottom layers. The relationships among these parameters were analyzed.
Magnetic and structural properties of hexagonal-close-packed-(CoCrPt)100−xCx thin films for poten... more Magnetic and structural properties of hexagonal-close-packed-(CoCrPt)100−xCx thin films for potential applications in magnetic recording media have been investigated. CrTi and Cr underlayers were used to improve the in-plane preferred orientation. High coercivity of 4.4 kOe and anisotropy of 3.6×106 erg/cm3 have been achieved in films with a CrTi underlayer after postdeposition annealing. The addition of Ti to the Cr underlayer results in lower annealing temperature and shorter annealing time, while retaining higher coercivity. Vibrating sample magnetometer measurements showed that the magnetic moment lies fairly well in the film plane under proper preparation conditions; while x-ray diffraction measurements showed that the CrTi underlayer promoted Co (10.0) in-plane preferred orientation. Grain isolation in the magnetic layer was improved by the segregated C and further enhanced by postdeposition annealing. The peak value of δM curves decreased upon annealing and changed to a negative value when higher annealing temperatures were applied, indicating that strong exchange coupling in as-deposited film decreased and changed to dipolar interaction dominance upon annealing.
The temperature dependence of the sputtering Ar pressure effects on magnetic properties and the c... more The temperature dependence of the sputtering Ar pressure effects on magnetic properties and the coercivity mechanism of Co(2 &/Pd(13 A) multilayers were studied as the sputtering Ar pressure varied from 3-15 mTorr and the temperature from 300 to 35 K. It is found that the roughness of the interfaces or film surface increases with increasing sputtering pressure, the anisotropy increases with decreasing temperature and increasing Ar pressure and shows a maximum at P,=12 mTorr, and the coercivity increases with Ar pressure and shows stronger temperature dependence at higher Ar pressure. The coercivity mechanism was analyzed in terms of the coercivity predicted by Kronmiiller's theory [Phys. Status Solidi B 144, 385 (1987)]. Wall pinning is found to be the main mechanism and the size of the pinning site increases slightly as the Ar pressure increases.
We report on the magnetic and magneto-optical properties of the intermetallic alloys MnS(Gel-nMXj... more We report on the magnetic and magneto-optical properties of the intermetallic alloys MnS(Gel-nMXj3, where M=Sn, Pb. Generally, these alloys were ordered ferromagnetically at Ta300 K for xcO.3. The structure of Mn,(Ge,-,Sn,)3 remains in the hexagonal Mn,Si,(/zPlh) phase up to x=0.25 and then changes to Ni,In (hP6) as x approaches 1. The magnetization and Curie temperature of these alloys is largest for small x and reach a minimum value near x = 0 .S. The room temperature Polar Kerr rotation, however, increases from-0.06" at s = 0 to maximum value of-0.12" atx=O.I before decreasing toward zero forx>O.3. The M.&Ge,-,Pb,), samples show a Mn,Si, structure with ferromagnetic behavior for x60.3, and varying structure with rapidly decreasing magnetization above x = 0.3. The magnetic behavior observed was compIex for x> 0.3. The Kerr rotation of the Pb-doped alloys in the ferromagnetic region monotonically decreases from-0.06" to zero at x-0.3.
Evolution of orientation distribution of Co͑110͒ crystal planes was determined by x-ray rocking c... more Evolution of orientation distribution of Co͑110͒ crystal planes was determined by x-ray rocking curves. It has been found that: ͑i͒ The full-width at half maximum W of the Co͑110͒ rocking curve decreases with both increasing Cr underlayer thickness d Cr , and increasing CoCrTa magnetic layer thickness d Co , especially in the thin layer regime. ͑ii͒ For the thin d Co regime, the interlayer diffusion between the Cr underlayer and the magnetic layer affects the rocking curves and magnetic properties significantly. ͑iii͒ Film magnetic properties, e.g., a significant jump in coercivity with increasing magnetic layer thickness in the thin d Co regime may be related in part to the evolution of the Co͑110͒ orientation distribution.
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