Magnetism in amorphous iron-boron alloys

Magnetic resonance and low field magnetization measurements show that, depending on concentration, there are three distinct magnetic regimes in amorphous Fe x B 100- x . In this paper a detailed description of a study of magnetism in these alloys is presented. A magnetic phase diagram is proposed and the resonance and magnetization measurements, in each of three regimes are discussed. For x > 50 the alloys appear to be normal amorphous ferromagnets when the measuring field is large (⩾ 1 kOe). However, measurements in smaller fields indicate that the alloys are not conventional ferromagnets since the spins are noncollinear. For the concentration range 41 ⩽ x ⩽ 50, the alloys are reentrant ferromagnets. While the ferromagnetic state is as discussed above, the low temperature state shows explicit nonergodic behavior besides showing many of the usual characteristics of spin glasses. In the neighborhood of the multicritical point, not only the paramagnet-ferromagnet transition temperature T C, but also the ferromagnet-spin glass transition temperature T f decreases as x is reduced . Ferromagnetism is absent at the low concentration end, 21 ⩽ x ⩽ 37, but Fe ions retain a paramagnetic moment and these alloys enter the spin glass state at low temperatures. In the intermediate concentration regime, 37 < x < 41, a more complex behavior is observed.