Evidence Of Spin Reorientation Research Articles

Evidence of spin reorientation in YbFe6Ge6 from neutron diffraction and 57Fe Mössbauer experiments

High-resolution neutron diffraction and 57Fe Mössbauer experiments have been performed on powder samples of the ternary intermetallic YbFe6Ge6. This compound crystallizes with a hexagonal structure (P6/mmm) which can be described as an ordered state intermediate between the HfFe6Ge6- and YCo6Ge6-type structures, with cell parameters suggesting that the Yb ion is in (or close to) a trivalent state. At room temperature, the Fe-sublattice magnetic arrangement consists of an antiferromagnetic stacking along the c-axis of the ferromagnetic (001) Fe planes with the easy direction of magnetization along [001]. Below about 85 K a spin-reorientation process occurs; a fraction (T) of the iron moments rotate abruptly from the c-axis to a given direction in or close to the basal plane. This phenomenon allows the observation of anisotropic contributions to the total hyperfine field at the Fe site. At 4.2 K, approximately 18% of the iron moments remain along the c-axis. No long-range magnetic order of the Yb sublattice is observed, at least above 1.5 K. We also report 57Fe Mössbauer investigations of the HfFe6Ge6-type LuFe6Ge6 compound.

Magnetic properties and structure of the intermetallic compounds

The effect of substitution of Fe for Co in the compounds (x = 0.0-0.5) on the crystal structure and magnetic properties has been investigated. The lattice parameters and the unit-cell volume of increase with x in the range . The magnetic moment per formula unit in increases linearly as the Fe concentration increases. The Curie temperature is found to increase for and then decrease for x > 0.1. The easy-magnetization direction changes from the easy-axis direction to the easy-plane direction (x = 0.4), and the anisotropy field decreases with the Fe substitution. Evidence for spin reorientation in the compounds for was observed in the M-T and curves.

Mössbauer spectroscopy investigation of the magnetic characteristics of Nd 2(Fe 0.8Co 0.1Mn 0.1) 14B

The 57Mössbauer spectra of Nd 2(Fe 0.8Co 0.1Mn 0.1) 14B in the temperature range of 100 to 700 K reveal several interesting features. T c, the Curie temperature, measured by the collapse of internal magnetic-hyperfine field ( B̄ hf) as well as by the method of thermal scanning of count rates in the central region of the spectra is found to be 625(5) K. This is in agreement with the value obtained from vibrational sample magnetometer measurements on the same sample. No evidence for spin reorientation like one in Nd 2Fe 14B could be obtained from our measurements. Similarly, no site preference of Mn atoms for particular Fe-sites could be observed from the present study. B̄ hf, the average field, on 57Fe nuclei at 300 K is 28.5(3) T. The magnetic moment of Fe atoms is estimated to decrease by ∼6% as a result of substitution of Mn and Co atoms by 10% each.

Magnetic and crystallographic properties of R<inf>2-x</inf>Pr<inf>x</inf>Co<inf>14</inf>B (R = Tb, Dy, Ho and Tm)

R 2 Co 14 B systems do not form in the characteristic Nd 2 Fe 14 B structure for rare earths heavier than Tb. They can be formed in this structure in the Dy, Ho and Tm systems when some of the heavy rare earth is replaced by Pr. The amount of Pr needed to stabilize the structure is the larger the smaller the heavy rare earth. All systems studied exhibit uniaxial anisotropy. Magnetizations and anisotropy fields increase with increasing x in the R 2-x Pr x Co 14 B systems. Evidence of spin reorientation is observed at temperatures ranging from 420 to 790 K. Introduction of Pr in place of R reduces the spin-reorientation temperature for R = Tb but increases it for R = Dy, Ho and Tm.

Effect of Hydrogen on Magnetic Properties of Quaternary Pr2Fe14−xCoxB Compounds

The effect of absorbed hydrogen on the structural and magnetic behavior of Pr2Fe14−xCoxB has been investigated. Introduction of hydrogen in the host material reduces the average magnetic moment of the 3d element by ˜ 4 to 7%. Anisotropy fields for all systems studied are significantly reduced upon hydrogenation. Evidence of spin reorientation at temperatures ranging between ˜ 295 K and 496 K for some of the hydrides is observed. Pr2Co14B and its hydride exhibit uniaxial anisotropy at room temperature and at 77 K.The role of hydrogen in expanding the lattices of these intermetallics and modifying their magnetic properties is discussed.

Mössbauer evidence of spin reorientation in single crystal Nd 2Fe 14B

Using 57Fe Mössbauer spectroscopy, we have measured the canting angle of the iron spins in Nd 2Fe 14B. Our measurements are made on a single crystal sample cut with its c-axis normal to the sample face. The iron spins rotate away from the c-axis by about 27° at 4.2 K.