n-Dependent variations of coercivity with temperature in [Co/Pt]n multilayers

In a series of [Co(5 Å)/Pt(6 Å)]n multilayers with perpendicular anisotropy, it has been observed that the coercivity HC shows an rapid increase as the temperature is decreased from 300 to 5 K. Above 220 K, HC is proportional to the repetition number n, that is to say, HC4 > HC3 > HC2 > HC1 (HCn, n is the repetition number), while at 60 K ≤ T≤ 210 K, n dependence of HC is HC3 > HC4 > HC2 > HC1. At 25 K ≤ T ≤ 55 K, HC as a function of the repetition number n can be expressed as HC2 > HC1 > HC3 > HC4, whereas below 20 K, the single Co layer of n = 1 shows the fastest increase, and the coercivity becomes the largest one, namely, HC1 > HC2 > HC3 > HC4. This observed n-dependent variations of coercivity with temperature can be attributed to surface roughness and temperature dependence of the saturation magnetization in the Co/Pt multilayers.