Spin structure of nanocrystalline terbium

Abstract

We present an experimental study of the magnetic microstructure in the nanocrystalline hard magnet Tb. Field-dependent small-angle neutron scattering ͑SANS͒ data are analyzed quantitatively in terms of the correlation function of the spin misalignment. We find that up to applied fields of several tesla the magnetization remains ''locked in'' to the basal planes of the hcp crystal lattice of each individual crystallite, but that the in-plane orientation of the spins is highly nonuniform within each grain. This spin disorder at the nanoscale can be suppressed by a large applied field, but in the remanent state the disorder reduces the magnetization to values considerably below the Stoner limit. In field-dependent SANS, the intragrain spin disorder gives rise to a crossover of the scattering curves, and to the unusual finding that the scattering cross section at small scattering vector increases with increasing magnetic field. As the origin of the internal spin disorder within the grains, we propose an extra magnetic anisotropy energy at small grain size, presumably due to microstrain, a suggestion which is supported by analysis of ac-susceptibility data in the paramagnetic state. Our finding of a reduced remanence at small grain size is contrary to the remanence enhancement that is observed in other nanocrystalline hard magnets. We also report an unusual logarithmic field dependence of the magnetization over wide ranges of the applied field and temperature.

Structural and magnetic properties of bulk nanocrystalline Erbium metal

“…17 The magnetization of the coarse-grained Er sample (259 emu/g under 9 T), for example, reaches only 86.3% of its saturation magnetization (300 emu/g). 7 The magnetization under 9 T of the two nanocrystalline Er samples annealed at 873 K and 573 K decreases by about 8.89% and 10.9%, respectively, compared with that of the coarse-grained Er samples. Note that for the coarse-grained Er sample, there is a sharp increase of the magnetization at about 1.63 T. This abnormal behavior results from intermediate fan structures jumping of the hard basal plane magnetic moment, 7 but it never appears in the nanocrystalline Er samples.…”

“…7 The magnetization under 9 T of the two nanocrystalline Er samples annealed at 873 K and 573 K decreases by about 8.89% and 10.9%, respectively, compared with that of the coarse-grained Er samples. Note that for the coarse-grained Er sample, there is a sharp increase of the magnetization at about 1.63 T. This abnormal behavior results from intermediate fan structures jumping of the hard basal plane magnetic moment, 7 but it never appears in the nanocrystalline Er samples. On the other hand, a remarkable increase of the coercive force of the samples from 797 Oe to 3319 Oe with the decrease of the average grain size was also observed, as shown in the inset figure in Figure 4.…”

“…As a result, some nanostructured heavy rare earth metals, including Gd, Tb, and Dy, have been prepared and widely studied for their structure and magnetic properties. [1][2][3][4][5][6][7][8][9][10] As one of the heavy rare earth elements, Erbium (Er) had been intensively studied for its complex magnetic structures and magnetic properties. [11][12][13][14][15][16][17][18] Er metal has hexagonal close packed (hcp) crystal structure, and it undergoes three differentmagnetic phase transitions below 100 K. At T N of 85 K, a c-axis modulated sinusoidal structure appears; then with decreasing temperature at T B of 52 K a basal plane modulated structure, namely a quasi anti-phase domain magnetic structure; finally at T C of 20 K a conical ferromagnetic structure.…”

Static and dynamic correlations in magnetic nanomaterials studied by small angle neutron scattering techniques

“…M ⊥ i is given in units of Bohr magnetons B and (e 2 /2mc 2 ) = 0.27 * 10 −12 cm. In two phase-systems (which we will consider throughout this paper) where particles are embedded in a homogeneous matrix the total scattering amplitude of the particle is called "form factor" and defined by F(QR) = ∫ dr 3 exp(iQr j ) = V p f(QR),…”

“…This non-destructive technique allows different types of inhomogeneities to be identified in crystalline, amorphous as well as in liquid materials [1][2][3]. In addition, spatial fluctuations of the magnetisation can be monitored due to the interaction between neutron spin and magnetic moments.…”