## Abstract

The magnetic ac susceptibility χ of oriented (Formula presented)Ac crystallites has been measured as a function of temperature, field, and frequency. The field has been applied at different values of the angle θ with respect to the sample easy axis. For T=5tK, the isothermal and adiabatic χ limits have been determined as a function of field. For θ=0° and intermediate frequencies, Lorentzian-shaped peaks have been observed at magnetic field values (Formula presented)=(Formula presented) with n=0, 1, and 2 where (Formula presented)=4.1tkOe. As θ increases these maxima shift to higher fields, that satisfy (Formula presented)cos θ=const, and decrease in amplitude. The relaxation time (Formula presented) follows Arrhenius' law with respect to temperature and decreases sharply at H=(Formula presented). The observed phenomenology unambiguously proves the existence of field-tuned tunneling between excited magnetic states which are thermally populated. At 5 K, the effective activation energy and the spin states involved in the tunneling process have been obtained.

Original language | English (US) |
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Pages (from-to) | 11448-11456 |

Number of pages | 9 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 55 |

Issue number | 17 |

DOIs | |

State | Published - 1997 |

Externally published | Yes |

## ASJC Scopus subject areas

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics