Huge Coercivity Research Articles

Coercivity exceeding 100kOe in epitaxially grown FePt sputtered films

Microstructure and magnetization processes of highly ordered FePt(001) films with large perpendicular magnetic anisotropy have been studied. The film morphology was controlled from assemblies of single-domain nanoparticles to those of multidomain islands by varying the nominal thickness (tN) of the FePt films sputter-deposited on a heated MgO(001) substrate. The change in the magnetization process from magnetization rotation to domain wall displacement is clearly demonstrated by the initial magnetization curves. Huge coercivities as high as 70 and 105kOe have been achieved in the film with single-domain particles at room temperature and 4.5K, respectively.

Synthesis and magnetic properties of Pr(Fe1-xCox)2 and Pr1-yTby(Fe0.4Co0.6)2 alloys

Measurement of X-ray diffraction, magnetization and magnetostriction was made on the Pr(Fe1-xCox)2 (x=0.4, 0.5 and 0.6) and Pr1-yTby(Fe0.4Co0.6)2 (y=0, 0.1, 0.2 and 0.3) alloy series. It was found that a cubic phase with the MgCu2 structure can be obtained in the Pr(Fe1-xCox)2 series only at x=0.6. The Pr1-yTby(Fe0.4Co0.6)2 system has the cubic MgCu2 structure over the studied range for y. The lattice constant and magnetization decrease and the Curie temperature increases with increasing y. At 7 K, Pr1-yTby(Fe0.4Co0.6)2 samples are found to have huge intrinsic coercivities, which are associated with narrow domain walls. It is also found from X-ray measurement that in Pr1-yTby(Fe0.4Co0.6)2 the spontaneous magnetostriction λ111 increases due to Tb substitution, while the saturation magnetostriction λs is much lower than λ111. This can be attributed to the large value of λ100 with an opposite sign to λ111, which may be caused by the filling of the d band due to Co substitution.

High coercivity and magnetic domain observation in epitaxially grown particulate FePt thin films

We have investigated the magnetic domains of high coercive FePt[001]/MgO[001] films with various morphologies by magnetic force microscopy (MFM). The film morphology changes from particulate to continuous depending on the film thickness ( t), accompanied by a drastic decrease in coercivity when t exceeds the critical thickness, t c=45 nm. The film with t=10 nm is comprised of only single-domain particles of approximately 50 nm, which has a huge coercivity as high as 40 kOe. The isolated particles larger than 200 nm are multi-domain, and the films containing these isolated particles show slightly lower coercivity. The coercivity drastically decreases with the percolation of the particles.

Microstructure and magnetic properties of FePt thin films epitaxially grown on MgO (0 0 1) substrates

We have investigated the microstructures and the magnetic properties of 10 nm thick FePt films epitaxially grown on MgO (0 0 1) substrates at various substrate temperatures, T s. The long-range-order parameter of the L1 0 structure and the coercivity increased above T s=450°C with a drastic change in the film morphology from continuous structure to island-like one. A huge coercivity of 42 kOe obtained at T s=700°C is attributed to complete magnetic isolation of nanometer-scale particles as well as perfect uniaxial alignment of c-axis in the normal direction to the film.

Fabrication and characterization of ordered FePt nanoparticles

Ordered FePt nanoparticles with unique magnetic properties were obtained by direct deposition of FePt and C onto heated substrates at temperature above 450 °C. The FePt particle sizes were controlled in the range from a few nanometers to 20 nm by adjusting the sputtering time from both the FePt and C targets. The tiny FePt nanoparticles (less than 3 nm) showed superparamagnetic behavior at room temperature. However, larger particles showed huge coercivities at room temperature (23 and 34 kOe for particles with average sizes of around 8 and 15 nm, respectively). For a certain FePt to C ratio, the films can show strong perpendicular anisotropy which is favorable for high density recording media.

Preparation and magnetic properties of highly coercive FePt films

The magnetization processes of highly ordered FePt(001) films with large perpendicular magnetic anisotropy have been studied. The film morphology was controlled from isolated particles to continuous film by varying the nominal thickness (tN) of the FePt film sputter deposited directly on a MgO(001) substrate at an elevated temperature. A drastic change in the coercivity by one order of magnitude has been found at the critical thickness (tN=45 nm) where the film morphology changes from a particulate to a continuous state. A huge coercivity exceeding 40 kOe has been achieved in the film with tN=10 nm, which comprises single domain particles with an average lateral size of approximately 50 nm.

Sm(Co, Cu, Ni) thin films with giant coercivity

Nanostructured Sm(Co, Ni, Cu) thin films have been obtained by heat treating as-deposited sputtered amorphous films. The room-temperature coercivity increases from less than 100 Oe in the amorphous state to 42 kOe in a SmCo2Cu3 sample annealed 30 min at 550 °C. Structural data in the optimum samples suggest a particle size around 10 mn. Magnetic viscosity measurements indicated that the switching volume is of the same order as the crystallite size. Remanence measurements showed that interparticulate interactions are magnetizing and rather independent of the crystallization stage. These data indicate that the huge coercivity enhancement is due to domain-wall pinning at high anisotropy Sm–Co precipitates.

Nanocrystalline Sm-Co-Cu(Ni) thin films with giant coercivity

Nanostructured Srn-Co, Sm-Co-C;u, Sm-Co-Ni thin films have been obtained by crystallizing the as-deposited amorphous films which were sputtered onto Cr buffer layers. Room temperature coercivity increases from less than 100 Oe in the amorphous state up to 42 kOe in a SmCo 2Cu 3 Sample annealed 30 min. at 550 °C. Initial magnetization curves showed a behavior characteristic of uniform domain wall pining. Magnetic viscosity measurements indicated that the switching volume is of the same order as the Sm(Co,Cu) 5 crystallites size. Remanence Measuremcnts showed that interparticulate interactions were magnetizing and rather independent of the crystallization static. These data pointed to domain wall pinning at the high anisotropy Sm-C′.o precipitatcs as the origin of the huge coercivity in the annealed films.

Magnetic study of SmCo5, PrCo5, SmCo4B, and Sm3Co11B4 under pulse high field

Magnetization curves and hysteresis loops for field-oriented powders of Smn+1Co3n+5B2n (n=0, 1, and 3) and PrCo5 were measured at T=4.2 K and partly at 77 K, under a strong pulsed field up to 36 T. Magnetic measurements for Smn+1Co3n+1B2n (n=1, 2, and 3) compounds were also performed. Huge anisotropy fields of 120 T for SmCo4B and of 130 T for Sm2Co7B3 were obtained. The Sm sublattice anisotropy of SmCo4B was found to be larger than that of SmCo5. To explain this, the Sm f-electron state for n≥ (R18)2 of Smn+1Co3n+5B2n has been expected to change from that for n≤1. Huge coercivities of 8 T and 27.5 T were observed at T=4.2 K for SmCo4B and for Sm2Co7B3 respectively. Magnetization processes for field-oriented PrCo5 at T=4.2 K were found to be similar to those of Nd2Fe14B at T=4.2 K.

MAGNETIC PROPERTIES OF RAPIDLY QUENCHED (Nd, Pr)2 (Fe,Co)14B-TYPE ALLOYS

The coercivity Hci of rapidly quenched Nd-Fe-B is linked to the multiphase structure of the alloys : high coercivities require the suppression of the FeNd solid solution and the exictence of the intergranular Nd-rich phase. In quarternary Pr-Fe-Co-B alloys Hci and the remanence Jr depend in the same way on Co content as in the Nd-Fe-Co-B system. However, compared with rapidly quenched Nd-Co-B samples, as-quenched Pr-Co-B alloys show huge coercivities as a result of the favourable intrinsic magnetic properties. Again, magnetic hardness is not only coupled to the grain size but also to the existence of secondary phases.

Formation of metastable compounds and magnetic properties in rapidly quenched (Fe1−x Cox)5Sm and (Fe1−xCox)7Sm2 alloy systems

The formation of metastable (TM)5Sm and (TM)7Sm2 (TM=Fe-Co) compounds and their magnetic properties have been investigatyed by the x-ray diffraction method and analysis of thermomagnetization curves for rapidly quenched (Fe1−x Cox)5Sm and (Fe1−x Cox)7Sm2 (0≤x≤1.0) alloys. The (Fe1−x Cox)5Sm compound is formed with a single phase in the range 0.7≤x≤1.0 and a mixture with other stable compounds in other composition range. On the other hand, the metastable (TM)7Sm2 compound exists in the mixed state with a large amount of (TM)3Sm stable compound in the range 0.7≤x≤1.0. The single phase (RM)5Sm compound exhibits a huge coercivity of 5–14 kOe.