  We address the electronically induced anisotropy field acting on a spin
moment comprised in a vibrating magnetic molecule located in the junction
between ferromagnetic metals. Under weak coupling between the electrons and
molecular vibrations, the nature of the anisotropy can be changed from favoring
a high spin (easy axis) magnetic moment to a low spin (easy plane) by applying
a temperature difference or a voltage bias across the junction. For unequal
spin-polarizations in the ferromagnetic metals it is shown that the character
of the anisotropy is essentially determined by the properties of the weaker
ferromagnet. By increasing the temperature in this metal, or introducing a
voltage bias, its influence can be suppressed such that the dominant
contribution to the anisotropy is interchanged to the stronger ferromagnet.
With increasing coupling strength between the molecular vibrations and the
electrons, the nature of the anisotropy is locked into favoring easy plane
magnetism.
