 Solution

An in-plane magnetic field lowers the Zeeman energy when moments align with it. It competes with antiferromagnetic interlayer exchange coupling; the layers generally cant or switch toward a parallel configuration and ultimately saturate if the field overcomes coupling and magnetic anisotropy. The high-resistance antiparallel state evolves toward the lower-resistance parallel state. The switching path and field scale depend on anisotropy, pinning and coupling strength, which are not numerically specified.